Decoding Honda ECU Codes: Your Comprehensive OBD2 Guide

Navigating car troubles can be daunting, especially when that check engine light illuminates on your Honda dashboard. Fortunately, modern vehicles, including Hondas, are equipped with sophisticated Engine Control Units (ECUs) and onboard diagnostic systems (OBD2) that can pinpoint potential problems. Understanding Honda ECU codes is the first step towards effective car maintenance and repair. This guide will walk you through how to retrieve and interpret these codes, empowering you to diagnose issues and communicate effectively with your mechanic.

Whether you are a seasoned DIY enthusiast or a Honda owner simply seeking to understand your vehicle better, this comprehensive guide to Honda ECU codes and OBD2 diagnostics is for you. We’ll break down the process of accessing these codes and provide a detailed list to help you understand what your Honda is trying to tell you.

Understanding Honda ECU and OBD2 Systems

Before diving into code retrieval, let’s briefly understand the key components:

ECU (Engine Control Unit): This is essentially your car’s computer, monitoring and controlling various engine functions for optimal performance and emissions.
OBD2 (On-Board Diagnostics II): A standardized system in most cars since the mid-1990s, OBD2 monitors vehicle systems and generates codes when it detects a malfunction. These codes are your car’s way of communicating problems.

When your check engine light comes on, it signifies that the ECU has detected an issue and stored a corresponding Diagnostic Trouble Code (DTC). These codes are invaluable for diagnosing the problem efficiently.

Accessing Honda ECU Codes: OBD2 Method

For most modern Hondas (generally post-1996), accessing ECU codes is straightforward using an OBD2 scanner.

Locate the OBD2 Port: This is typically found under the dashboard on the driver’s side. It’s a 16-pin connector, trapezoidal in shape.

Alt text: Location of the OBD2 diagnostic port under the steering wheel in a Honda vehicle.
Plug in the OBD2 Scanner: With the ignition off, plug your OBD2 scanner into the port.
Turn Ignition to “ON” Position: Turn the key to the “ON” position without starting the engine. This powers up the car’s electronics and allows the scanner to communicate with the ECU.
Follow Scanner Instructions: Each OBD2 scanner varies slightly, but generally, you’ll need to select “Read Codes” or similar option. The scanner will then retrieve and display any stored DTCs.
Record the Codes: Note down all the codes displayed. They usually start with a letter (P, B, C, or U) followed by four numbers. For example, P0171.

Accessing Honda ECU Codes: OBD1 Method (for Older Models)

For older Honda models (roughly 1992-1995), the process is a bit different as they utilize the older OBD1 system. You’ll need to use a jumper wire to retrieve the codes.

Locate the ECU and Service Connector:
- On the passenger side, locate the kick panel carpet.
- Lift up the carpet to expose the ECU.
- Above the ECU, you’ll find a small, usually grey, 2-pin connector (Service Check Connector).
Alt text: Honda ECU location behind the passenger side kick panel, showing the service check connector for OBD1 code retrieval.
Prepare the Jumper Wire: Take a small piece of speaker wire and strip both ends to expose the copper. Twist the copper strands at each end to create pointed tips.
Insert Jumper Wire:
- Plug one end of the jumper wire into one socket of the 2-pin connector.
- Insert the other end into the other socket. It doesn’t matter which wire goes into which socket.
Alt text: Close-up view of a jumper wire correctly inserted into the OBD1 service check connector in a Honda vehicle.
Turn Ignition to “ON” Position: Turn the ignition to the “ON” position (don’t start the car).
Read the Check Engine Light Flashes: Watch the check engine light on your instrument cluster. It will flash in patterns to indicate the codes.
- Long Flash: Represents 10.
- Short Flashes: Represent 1.
For example:
- !.....!!! (One long flash, then three short flashes) = Code 13
- !....!....!!!!! (Two long flashes, then five short flashes) = Code 25
Record the Codes: Note down all the codes based on the flash patterns.

Honda ECU OBD1 Code List

Here is a list of common OBD1 Honda ECU codes and their descriptions:

1: O2A – Oxygen sensor #1
2: O2B – Oxygen sensor #2
3: MAP – Manifold Absolute Pressure sensor
4: CKP – Crank Position sensor
5: MAP – Manifold Absolute Pressure sensor
6: ECT – Engine Coolant Temperature sensor
7: TPS – Throttle Position sensor
8: TDC – Top Dead Center sensor
9: CYP – Cylinder sensor
10: IAT – Intake Air Temperature sensor
12: EGR – Exhaust Gas Recirculation lift valve
13: BARO – Atmospheric Pressure sensor
14: IAC (EACV) – Idle Air Control Valve
15: Ignition output signal
16: Fuel injectors
17: VSS – Vehicle Speed Sensor
19: Automatic transmission lockup control valve
20: Electrical Load Detector
21: VTEC spool solenoid valve
22: VTEC pressure valve
23: Knock sensor
30: Automatic transmission A signal
31: Automatic transmission B signal
36: Traction control (JDM ECUs)
41: Primary oxygen sensor heater
43: Fuel supply system
45: Fuel system too rich or lean
48: LAF – Lean Air Fuel sensor
54: CKF – Crank Fluctuation sensor
58: TDC sensor #2
61: Primary oxygen sensor
63: Secondary oxygen sensor
65: Secondary oxygen sensor heater
71: Random misfire cylinder 1
72: Random misfire cylinder 2
73: Random misfire cylinder 3
74: Random misfire cylinder 4

Honda ECU OBD2 Code List (P-Codes)

OBD2 codes are more standardized across manufacturers. Honda OBD2 codes typically follow the P-code format (Powertrain). Here is an extensive list of common Honda OBD2 P-codes:

P0010: Variable Valve Timing Control (VTC) Oil Control Solenoid Valve Malfunction
P0011: Variable Valve Timing Control (VTC) System Malfunction
P0101: Mass Airflow (MAF) Sensor Range/Performance Problem
P0102: Mass Airflow (MAF) Sensor Circuit Low Voltage
P0103: Mass Airflow (MAF) Sensor Circuit High Voltage
P0106: Manifold Absolute Pressure (MAP) Sensor Range/Performance Problem
P0107: Manifold Absolute Pressure (MAP) Sensor Circuit Low Voltage
P0108: Manifold Absolute Pressure (MAP) Sensor Circuit High Voltage
P0111: Intake Air Temperature (IAT) Sensor Circuit Range/Performance Problem
P0112: Intake Air Temperature (IAT) Sensor Circuit Low Voltage
P0113: Intake Air Temperature (IAT) Sensor Circuit High Voltage
P0116: Engine Coolant Temperature (ECT) Sensor Circuit Range/Performance Problem
P0117: Engine Coolant Temperature (ECT) Sensor Circuit Low Input
P0118: Engine Coolant Temperature (ECT) Sensor Circuit High Input
P0122: Throttle Position (TP) Sensor Circuit Low Input
P0123: Throttle Position (TP) Sensor Circuit High Input
P0125: Engine Coolant Temperature (ECT) Sensor Slow Response
P0128: Cooling System Malfunction
P0131: Primary Heated Oxygen Sensor (Primary HO2S) (Sensor 1) Circuit Low Voltage
P0132: Primary Heated Oxygen Sensor (Primary HO2S) (Sensor 1) Circuit High Voltage
P0133: Rear Air/Fuel Ratio (A/F) Sensor (Bank 1, Sensor 1) Circuit Slow Response
P0134: Air/Fuel Ratio (A/F) Sensor (Sensor 1) No Activity Detected
P0135: Primary Heated Oxygen Sensor (Primary HO2S) (Sensor 1) Heater Circuit Malfunction
P0137: Secondary Heated Oxygen Sensor (Secondary HO2S) Circuit Low Voltage
P0138: Secondary Heated Oxygen Sensor (Secondary HO2S) Circuit High Voltage
P0139: Secondary Heated Oxygen Sensor (Secondary HO2S) Slow Response
P0141: Secondary Heated Oxygen Sensor (Secondary HO2S) (Sensor 2) Heater Circuit Malfunction
P0143: Third Heated Oxygen Sensor (Third HO2S) (Sensor 3) Circuit Low Voltage
P0144: Third Heated Oxygen Sensor (Third HO2S) (Sensor 3) Circuit High Voltage
P0145: Third Heated Oxygen Sensor (Third HO2S) (Sensor 3) Circuit Slow Response
P0147: Third Heated Oxygen Sensor (Third HO2S) (Sensor 3) Heater Circuit Malfunction
P0153: Front Air/Fuel Ratio (A/F) Sensor (Bank 2, Sensor 1) Circuit Slow Response
P0154: Front Air/Fuel Ratio (A/F) Sensor (Bank 2, Sensor 1) Heater System Malfunction
P0155: Front Air/Fuel Ratio (A/F) Sensor (Bank 2, Sensor 1) Heater Circuit Malfunction
P0157: Front Secondary Heated Oxygen Sensor (Secondary HO2S) (Bank 2, Sensor 2) Circuit Low Voltage
P0158: Front Secondary Heated Oxygen Sensor (Secondary HO2S) (Bank 2, Sensor 2) Circuit High Voltage
P0159: Front Secondary Heated Oxygen Sensor (Secondary HO2S) (Bank 2, Sensor 2) Circuit Slow Response
P0161: Front Secondary Heated Oxygen Sensor (Secondary HO2S) (Bank 2, Sensor 2) Heater Circuit Malfunction
P0171: Fuel System Too Lean
P0172: Fuel System Too Rich
P0174: Front Bank (Bank 2) Fuel System Too Lean
P0175: Front Bank (Bank 2) Fuel System Too Rich
P0191: Fuel Pressure Sensor Range/Performance Problem
P0192: Fuel Pressure Sensor Circuit Low Voltage
P0193: Fuel Pressure Sensor Circuit High Voltage
P0196: EOT Sensor/Range Performance Problem
P0197: EOT Sensor Circuit Low Voltage
P0198: EOT Sensor Circuit High Voltage
P0222: Throttle Position (TP) Sensor 2 Circuit Low Voltage
P0223: Throttle Position (TP) Sensor 2 Circuit High Voltage
P0300: Random Misfire
P0301: No. 1 Cylinder Misfire
P0302: No. 2 Cylinder Misfire
P0303: No. 3 Cylinder Misfire
P0304: No. 4 Cylinder Misfire
P0305: No. 5 Cylinder Misfire
P0306: No. 6 Cylinder Misfire
P0325: Knock Sensor Circuit Malfunction
P0335: Crankshaft Position (CKP) Sensor Circuit No Signal
P0336 P0339: Crankshaft Position (CKP) Sensor Circuit Intermittent Interruption
P0340: Camshaft Position (CMP) Sensor No Signal
P0341: Camshaft Position (CMP) Sensor A Intermittent Interruption
P0341: Variable Valve Timing Control (VTC) Phase Gap
P0344: Camshaft Position (CMP) Sensor Intermittent Interruption
P0365: Camshaft Position (CMP) Sensor B No Signal
P0366 P0369: Camshaft Position (CMP) Sensor B Intermittent Interruption
P0385: Crankshaft Position (CKP) Sensor B No Signal
P0389: Crankshaft Position (CKP) Sensor B Intermittent Interruption
P0401: Exhaust Gas Recirculation (EGR) Insufficient Flow
P0404: Exhaust Gas Recirculation (EGR) Control Circuit Range/Performance Problem
P0406: Exhaust Gas Recirculation (EGR) Valve Position Sensor Circuit High Voltage
P0410: Air Pump Circuit Malfunction
P0411: Secondary Air Injection System Incorrect Flow
P0420: Catalyst System Efficiency Below Threshold
P0430: Front Bank Catalyst System Efficiency Below Threshold (Bank 2)
P0441: Evaporative Emission (EVAP) Control System Incorrect Purge Flow
P0442: Evaporative Emission (EVAP) System Small Leak Detected
P0443: Evaporative Emission (EVAP) Canister Purge Valve Circuit Malfunction
P0451: Fuel Tank Pressure (FTP) Sensor Range/Performance Problem
P0452: Fuel Tank Pressure (FTP) Sensor Circuit Low Voltage
P0453: Fuel Tank Pressure (FTP) Sensor Circuit High Voltage
P0456: Evaporative Emission (EVAP) System Very Small Leak Detected
P0457: Evaporative Emission (EVAP) System Leak Detected Fuel Fill Cap Loose/Off
P0461: Fuel Gauge Sending Unit Range/Performance Problem
P0462: Fuel Gauge Sending Unit Circuit Low Voltage
P0463: Fuel Gauge Sending Unit Circuit High Voltage
P0496: Evaporative Emission (EVAP) System High Purge Flow
P0497: Evaporative Emission (EVAP) System Low Purge Flow
P0498: Evaporative Emission (EVAP) Canister Vent Shut Valve Control Circuit Low Voltage
P0499: Evaporative Emission (EVAP) Canister Vent Shut Valve Control Circuit High Voltage
P0500: Vehicle Speed Sensor (VSS) Circuit Malfunction
P0501: Vehicle Speed Sensor (VSS) Range/Peformance Problem
P0505: Idle Control System Malfunction
P0506: Idle Control System RPM Lower Than Expected
P0507: Idle Control System RPM Higher Than Expected
P0511: Idle Air Control (IAC) Valve Circuit Malfunction
P0521: EOP Sensor Range/Performance Problem
P0522: EOP Sensor Circuit Low Voltage
P0523: EOP Sensor Circuit High Voltage
P0560: ECM Back-up Circuit Low Voltage
P0563: Engine Control Module (ECM)/Powertrain Control Module (PCM) Power Source Circuit Unexpected Voltage
P0600: Multiplex Control System Troubleshooting
P0603: ECM/PCM Internal Control Module Keep Alive Memory (KAM) Error
P0606: ECM/PCM Processor Malfunction
P0661: Intake Manifold Runner Control (IMRC) Valve Position Sensor Circuit Low Voltage
P0662: Intake Manifold Runner Control (IMRC) Valve Position Sensor Circuit High Voltage
P0685: ECM/PCM Power Relay Control Circuit Malfunction
P0700: Automatic Transmission Control System
P0705: Short in Transmission Range Switch Circuit (Multiple Shift-position Input)
P0706: Open in Transmission Range Switch Circuit
P0710 P0711: Problem in ATF Temperature Sensor Circuit
P0712: Short in ATF Temperature Sensor Circuit
P0713: Open in ATF Temperature Sensor Circuit
P0715 P0716: Problem in Mainshaft Speed Sensor Circuit
P0717: Problem in Mainshaft Speed Sensor Circuit (No Signal Input)
P0718: Mainshaft Speed Sensor Intermittent Failure
P0720: Countershaft Speed Sensor Circuit Malfunction
P0720 P0721: Problem in Countershaft Speed Sensor Circuit
P0722: Problem in Countershaft Speed Sensor Circuit (No Signal Input)
P0723: Countershaft Speed Sensor Intermittent Failure
P0725: Engine Speed Input Circuit Malfunction
P0730: Problem in Shift Control System
P0731: Problem in 1st Clutch and 1st Clutch Hydraulic Circuit
P0732: Problem in 2nd Clutch and 2nd Clutch Hydraulic Circuit
P0733: Problem in 3rd Clutch and 3rd Clutch Hydraulic Circuit
P0734: Problem in 4th Clutch and 4th Clutch Hydraulic Clutch
P0735: Problem in 5th Clutch and 5th Clutch Hydraulic Circuit
P0740: Problem in Lock-up Control System
P0741: Torque Converter Clutch Hydraulic Clutch Stuck OFF
P0743: Problem in Torque Converter Clutch Solenoid Valve Circuit
P0745: Problem in Hydraulic Control System of A/T Clutch Pressure Control Solenoid Valve A Circuit
P0746: A/T Clutch Pressure Control Solenoid Valve A Stuck OFF
P0747: A/T Clutch Pressure Control Solenoid Valve A Stuck ON
P0748: Problem in A/T Clutch Pressure Control Solenoid Valve A Circuit
P0750: Problem in Hydraulic Control System of Shift Solenoid Valve A Circuit
P0751: Shift Solenoid Valve A Stuck OFF
P0752: Shift Solenoid Valve A Stuck ON
P0753: Problem in Shift Solenoid Valve A Circuit
P0756: Shift Solenoid Valve B Stuck OFF
P0757: Shift Solenoid Valve B Stuck ON
P0758: Problem in Shift Solenoid Valve B Circuit
P0761: Shift Solenoid Valve C Stuck OFF
P0762: Shift Solenoid Valve C Stuck ON
P0763: Problem in Shift Solenoid Valve C Circuit
P0771: Shift Solenoid Valve E Stuck OFF
P0773: Problem in Shift Solenoid Valve E Circuit
P0775: Problem in the Hydraulic Control System of A/T Clutch Pressure Control Solenoid Valve B Circuit
P0776: A/T Clutch Pressure Control Solenoid Valve B Stuck OFF
P0777: A/T Clutch Pressure Control Solenoid Valve B Stuck ON
P0778: Problem in A/T Clutch Pressure Control Solenoid Valve B Circuit
P0780: Problem in Shift Control System
P0795: Problem in Hydraulic Control System of A/T Clutch Pressure Control Solenoid Valve C Circuit
P0796: A/T Clutch Pressure Control Solenoid Valve C Stuck OFF
P0797: A/T Clutch Pressure Control Solenoid Valve C Stuck ON
P0798: Problem in A/T Clutch Pressure Control Solenoid Valve C Ciruit
P0812: Open in Transmission Range Switch ATP RVS Switch Circuit
P0842: Short in 2nd Clutch Transmission Fluid Pressure Switch Clutch, or 2nd Clutch Transmission Fluid Pressure Switch (Clutch) Stuck ON
P0843: Open in 2nd Clutch Transmission Fluid Pressure Switch Circuit, or 2nd Clutch Transmission Fluid Pressure Switch Stuck OFF
P0845: Problem in 3rd Clutch Pressure Switch Circuit
P0847: Short in 3rd Clutch Transmission Fluid Pressure Switch Circuit, or 3rd Clutch Transmission Fluid Pressure Switch Stuck ON
P0848: Open in 3rd Clutch Transmission Fluid Pressure Switch Circuit, or 3rd Clutch Transmission Fluid Pressure Switch Stuck OFF
P0872: Short in 4th Clutch Transmission Fluid Pressure Switch Circuit, or 4th Clutch Transmission Fluid Pressure Switch Stuck ON
P0873: Open in 4th Clutch Transmission Fluid Pressure Switch Circuit, or 4th Clutch Transmission Fluid Pressure Switch Stuck OFF
P0962: Problem in A/T Clutch Pressure Control Solenoid Valve A Circuit
P0963: Problem in A/T Clutch Pressure Control Solenoid Valve A
P0966: Problem in A/T Clutch Pressure Control Solenoid Valve B Circuit
P0967: Problem in A/T Clutch Pressure Control Solenoid Valve B
P0970: Problem in A/T Clutch Pressure Control Solenoid Valve C Circuit
P0971: Problem in A/T Clutch Pressure Control Solenoid Valve C
P0973: Short in Shift Solenoid Valve A Circuit
P0974: Open in Shift Solenoid Valve A Circuit
P0976: Short in Shift Solenoid Valve B Circuit
P0977: Open in Shift Solenoid Valve B Circuit
P0979: Short in Shift Solenoid Valve C Circuit
P0980: Open in Shift Solenoid Valve C Circuit
P0982: Short in Shift Solenoid Valve D Circuit
P0983: Open in Shift Solenoid Valve D Circuit
P0985: Short in Shift Solenoid Valve E Circuit
P0986: Open in Shift Solenoid Valve E Circuit
P1020: Valve Pause System Stuck Off
P1021: Valve Pause System Stuck On
P1025: Valve Pause System Sticking Off
P1026: Valve Pause System Sticking On
P1077: Intake Manifold Runner Control (IMRC) System Malfunction (Low rpm)
P1078: Intake Mainfold Runner Control (IMRC) System Malfunction (High rpm)
P1106: Barometric Pressure (BARO) Sensor Circuit Range/Performance Problem
P1107: Barometric Pressure (BARO) Sensor Circuit Low Voltage
P1108: Barometric Pressure (BARO) Sensor Circuit High Voltage
P1121: Throttle Position (TP) Sensor Lower Than Expected
P1122: Throttle Position (TP) Sensor Higher Than Expected
P1128: Manifold Absolute Pressure (MAP) Sensor Circuit Lower Than Expected
P1129: Manifold Absolute Pressure (MAP) Sensor Circuit Higher Than Expected
P1130: Demand for Changing Both Secondary Heated Oxygen Sensor (Secondary HO2S) (Sensor 2) and Third Heated Oxygen Sensor (Third HO2S) (Sensor 3)
P1149: Air/Fuel Ratio (A/F) Sensor (Sensor 1) Range/Performance Problem
P1149: Air/Fuel Ratio Sensor (Sensor 1) Circuit Lean Range
P1157: Air/Fuel Ratio (A/F) Sensor (Sensor 1) AFS Line High Voltage
P1157: Air/Fuel Ratio (A/F) Sensor (Sensor 1) Circuit High Voltage
P1157: Air/Fuel Ratio (A/F) Sensor (Sensor 1) Range/Performance Problem
P1158: Air/Fuel Ratio (A/F) Sensor (Sensor 1) AFS- Terminal Low Voltage
P1159: Air/Fuel Ratio (A/F) Sensor (Sensor 1) AFS+ Terminal Low Voltage
P1162: Air/Fuel Ratio (A/F) Sensor (Sensor 1) Slow Response
P1163: Air/Fuel Ratio (A/F) Sensor (Sensor 1) Slow Response
P1163: Air/Fuel Ratio Sensor (Sensor 1) Slow Response
P1164: Air/Fuel Ratio (A/F) Sensor (Sensor 1) Range/Performance Problem
P1164: Air/Fuel Ratio (AF) Sensor (Sensor 1) Circuit Range/Performance
P1165: Air/Fuel Ratio (A/F) Sensor (Sensor 1) Range/Performance Problem
P1165: Air/Fuel Ratio Sensor (Sensor 1) Circuit Range/Performance
P1166: Air/Fuel Ratio (A/F) Sensor (Sensor 1) Heater System Electrical Problem
P1166: Heated Oxgen Sensor Sensor1 (Primary HO2S) Heater Circuit Malfunction
P1167: Air/Fuel Ratio (A/F) Sensor (Sensor 1) Heater System Malfunction
P1167: Heated Oxygen Sensor Sensor1 (Primary LAF HO2S) Heater System Malfunction
P1168: Air/Fuel Ratio (A/F) Sensor (Sensor 1) LABEL Low Voltage
P1169: Air/Fuel Ratio (A/F) Sensor (Sensor 1) LABEL High Voltage
P1182: Fuel Temperature Sensor Circuit Low Voltage
P1183: Fuel Temperature Sensor Circuit High Voltage
P1253 P1259: VTEC System Malfunction
P1297: Electric Load Detector (ELD) Circuit Low Voltage
P1298: Electric Load Detector (ELD) Circuit High Voltage
P1300: Random Misfire
P1324: Knock Sensor Power Source Circuit Low Voltage
P1336: Engine Speed (RPM) Fluctuation Sensor Intermittent Interruption
P1337: Engine Speed (RPM) Fluctuation Sensor No Signal
P1355: Front Ignition Coil Power Circuit Malfunction
P1359: Crankshaft Position (CKP)/Top Dead Center (TDC) Sensor Circuit Malfunction
P1361: Camshaft Position (CMP) Sensor A (Top Dead Center (TDC) Sensor) Intermittent Interruption
P1361: Top Dead Center (TDC) Sensor Intermittent Interruption
P1362: Camshaft Position (CMP) Sensor A (Top Dead Center (TDC) Sensor) No Signal
P1362: Top Dead Center (TDC) Sensor No Signal
P1366: Camshaft Position (CMP) Sensor B (Top Dead Center (TDC) Sensor) Intermittent Interruption
P1366: Top Dead Center (TDC) Sensor 2 Intermittent Interruption
P1367: Camshaft Position (CMP) Sensor B (Top Dead Center (TDC) Sensor) No Signal
P1367: Top Dear Center (TDC) Sensor 2 No Signal
P1381: Cylinder Position (CYP) Sensor Intermittent Interruption
P1382: Cylinder Position (CYP) Sensor No Signal
P1410: Air Pump Malfunction
P1415: Air Pump Electric Current Sensor Circuit Low Voltage
P1416: Air Pump Electric Current Sensor Circuit High Voltage
P1420: Nox Adsorptive Catalyst System Efficiency Below Threshold
P1438: Motor Drive Module (MDM) Overheating Signal Circuit
P1438: Motor Drive Module (MDM) Overheating
P1439: Motor Drive Module (MDM) Short Circuit Sensor Problem
P1439: Motor Drive Module (MDM) Short Circuit
P1440: IMA System Problem
P1445: Bypass Control Problem
P1448 P1449: Battery Module Overheating
P1449: Battery Cell Overheating
P1449: Battery Module Individual Voltage Input Deviation
P1449: Battery Module Deterioration
P1449: Battery Module Deviation
P1454: Fuel Tank Pressure (FTP) Sensor Range/Performance Problem
P1456: Evaporative Emissions (EVAP) Control System Leakage (Fuel Tank System)
P1457: Evaporative Emissions (EVAP) Control System Leakage (EVAP Canister System)
P1459: Evaporative Emission (EVAP) Purge Flow Switch Malfunction
P1491: Exhaust Gas Recirculation (EGR) Valve Insufficient Lift
P1486: Cooling System Malfunction
P1491: Exhaust Gas Recirculation (EGR) Valve Insufficient Lift
P1498: Exhaust Gas Recirculation (EGR) Valve Position Sensor Circuit High Voltage
P1505: Positive Crankcase Ventilation (PCV) Air Leakage
P1508 P1519: Idle Air Control Valve (IACV) Circuit Malfunction
P1509: Idle Air Control Valve (IACV) Circuit Failure
P1522: Brake Booster Pressure Sensor Circuit Low Voltage
P1523: Brake Booster Pressure Sensor Circuit High Voltage
P1524: Brake Booster Pressure Sensor Range/Performance Problem
P1541: Climate Control Unit Signal Circuit Low Voltage
P1542: Climate Control Unit Signal Circuit High Voltage
P1565: Motor Commutation Signal Problem
P1568: Battery Module Individual Voltage Input Problem
P1568: Battery Module Temperature Signal Circuit Problem
P1568: Battery Cell Temperature Signal Circuit Problem
P1572: Motor Drive Module (MDM) Temperature Signal Circuit Low Input
P1572: Motor Drive Module (MDM) Temperature Signal Circuit High Input
P1576: Motor Drive Module (MDM) Voltge Signal Circuit Low Input
P1577: High Voltage Detection Signal Circuit Problem
P1580: Battery Current Circuit Problem
P1581: Motor Power Inverter (MPI) Module Current Signal Circuit Low Input
P1581: Motor Power Inverter (MPI) Module Current Signal Circuit High Input
P1581: Motor Power Inverter (MPI) Module Current Signal Circuit Problem
P1582: Motor Current U Phase Signal Circuit Low Input
P1582: Motor Current U Phase Signal Circuit High Input
P1583: Motor Current V Phase Signal Circuit Low Input
P1583: Motor Current V Phase Signal Circuit High Input
P1584: Motor Current W Phase Signal Circuit Low Input
P1584: Motor Current W Phase Signal Circuit High Input
P1585: Motor Current Signal Circuit Problem
P1586: Motor Power Inverter (MPI) Module Current Signal/Battery Current Signal Circuit Problem
P1607: Engine Control Module (ECM)/Powertrain Control Module (PCM) Internal Circuit Malfunction
P1630: Transmission Control Module
P1635: Battery Condition Monitor (BCM) Module Proble
P1639: MOTB Signal Circuit Malfunction
P1640: ACTTRQ Motor Torque Signal Circuit Low Input
P1641: ACTTRQ Motor Torque Signal Circuit High Input
P1642: QBATT Battery Signal Circuit Low Input
P1643: QBATT Battery Signal Circuit High Input
P1644: MOTFSA Signal Malfunction
P1645: MOTFSB Signal Malfunction
P1646: MOTSTB Signal Malfunction
P1647: Power Command Signal Circuit Low Input
P1647: Power Command Signal Circuit High Input
P1647: Engine Torque Signal Circuit Low Input
P1647: Engine Torque Signal Circuit High Input
P1647: Mode Signal Circuit 1 Low Input
P1647: Mode Signal Circuit 1 High Input
P1647: Mode Signal Circuit 2 Problem
P1647: Engine Speed Signal Circuit Problem
P1648: Battery Condition Monitor (BCM) Module Communication Signal Circuit Problem
P1648: Motor Control Module (MCM) Communication Signal Circuit Problem
P1655: CVT-FI TMA/TMB Signal Line Failure
P1656: Problem in PCM-toVTM-4 Control Unit Communications Circuit
P1660: A/T-FI Data Line Failure/TCM – ECM Halt
P1676 P1678: FPTDR Signal Line Failure
P1679: RSCD Signal Circuit Malfunction
P1681: A/T FI Signal A Cicuit Low Voltage
P1682: A/T FI Signal A Circuit High Voltage
P1683: Throttle Valve Default Position Spring Performance Problem
P1684: Throttle Valve Return Spring Performance Problem
P1686: A/T FI Signal B Circuit Low Voltage
P1687: A/T FI Signal B Circuit High Voltage
P1705: Short in Transmission Range Switch Circuit (More than one range position is on at the same time)
P1706: Open in Transmission Range Switch Circuit
P1709: Problem Transmission Gear Selection Switch Circuit
P1730: Problem in Shift Control System: Shift Solenoid Valve A and D Stuck OFF Shift Solenoid Valve B Stuck ON Shift Valves A, B, and D Stuck
P1731: Problem in Shift Control System: Shift Solenoid Valve E Stuck ON Shift Valve E Stuck A/T Clutch Pressure Control Solenoid Valve A Stuck OFF
P1732: Problem in Shift Control System: Shift Solenoid Valve B and C Stuck ON Shift Valves B and C Stuck
P1733: Problem in Shift Control System: Shift Solenoid Valve D Stuck ON Shift Valve D Stuck A/T Clutch Pressure Control Solenoid Valve C Stuck OFF
P1734: Problem in Shift Control System: Shift Solenoid Valves B and C Stuck ON Shift Valves B and C Stuck
P1738: Problem in 2nd Clutch Pressure Switch Circuit
P1739: Problem in 3rd Clutch Pressure Switch Circuit
P1740: Problem in 4th Clutch Pressure Switch Circuit
P1750: Mechanical Problem in Hydraulic Control System of A/T Clutch Pressure Control Solenoid Valve Assemblies A and B, or Problem in the Hydraulic Control System
P1751: Mechanical Problem in Hydraulic Control System of Shift Solenoid Valve B and A/T Clutch Pressure Control Solenoid Valves A and B, or Problem in the Hydraulic Control System
P1753: Problem in Torque Converter Clutch Solenoid Valve Circuit
P1751 P1768: Problem in Torque Converter Clutch Solenoid Valve B Circuit
P1773: Problem in A/T Clutch Pressure Control Solenoid Valve B Circuit
P1790: Throttle Position (TP) Sensor Circuit Malfunction
P1791: Vehicle Speed Sensor (VSS) Range/Performance Problem
P1792: Problem in Engine Coolant Temperature (ECT) Sensor Circuit
P1793: Manifold Absolute Pressure Sensor Circuit
P1870: Problem in CVT Speed Change Control Valve Assembly Circuit
P1873: Problem in CVT Pulley Pressure Control Valve Assembly Circuit
P1879: Problem in CVT Start Clutch Pressure Control Valve Assembly Circuit
P1882: Problem in Inhibitor Solenoid Circuit
P1884: Secondary Gear Speed Sensor 2 Circuit Malfunction
P1885: CVT Drive Pulley Speed Sensor Circuit
P1886: CVT Driven Pulley Speed Sensor Circuit
P1888: CVT Speed Sensor
P1889: Problem in CVT Speed Sensor 2 Circuit
P1890: Shift Control System
P1891: Problem in Start Clutch System
P1894: CVT Speed Change Control Valve Circuit
P1895: CVT Pulley Pressure Control Valve Circuit
P2101: Throttle Actuator System Malfunction
P2108: Throttle Actuator Control Module Problem
P2118: Throttle Actuator Current Range/Performance Problem
P2122: Accelerator Pedal Position (APP) Sensor 1 (Throttle Position Sensor D) Circuit Low Voltage
P2123: Accelerator Pedal Position (APP) Sensor 1 (Throttle Position Sensor D) Circuit High Voltage
P2127: Accelerator Pedal Position (APP) Sensor 2 (Throttle Position Sensor E) Circuit Low Voltage
P2128: Accelerator Pedal Position (APP) Sensor 2 (Throttle Position Sensor E) Circuit High Voltage
P2135: Throttle Position (TP) Sensor 1/2 Incorrect Voltage Correlation
P2138: Accelerator Pedal Position (APP) Sensor 1/2 (Throttle Position Sensor D/E) Incorrect Voltage Correlation
P2176: Throttle Actuator Control System Idle Position Not Learned
P2195: Air/Fuel Ratio (A/F) Sensor (Sensor 1) Signal Stuck Lean
P2197: Front Air/Fuel Ratio (A/F) Sensor (Bank 2, Sensor 1) Signal Stuck Lean
P2227: Barometric Pressure (BARO) Sensor Circuit Range/Performance Problem
P2228: Barometric Pressure (BARO) Sensor Circuit Low Voltage
P2229: Barometric Pressure (BARO) Sensor Circuit High Voltage
P2237: Rear Air/Fuel Ratio (A/F) Sensor (Bank 1, Sensor 1) IP Line High Voltage
P2238: Air/Fuel Ratio (A/F) Sensor (Sensor 1) AFS+ Line Low Voltage
P2238: Rear Air/Fuel Ratio (A/F) Sensor (Bank 1, Sensor 1) IP Line Low Voltage
P2240: Front Air/Fuel Ratio (A/F) Sensor (Bank 2, Sensor 1) IP Line High Voltage
P2241: Front Air/Fuel Ratio (A/F) Sensor (Bank 2, Sensor 1) IP Line Low Voltage
P2243: Rear Air/Fuel Ratio (A/F) Sensor (Bank 1, Sensor 1) VCENT Line High Voltage
P2245: Rear Air/Fuel Ratio (A/F) Sensor (Bank 1, Sensor 1) VCENT Line Low Voltage
P2247: Front Air/Fuel Ratio (A/F) Sensor (Bank 2, Sensor 1) VCENT Line High Voltage
P2249: Front Air/Fuel Ratio (A/F) Sensor (Bank 2, Sensor 1) VCENT Line Low Voltage
P2251: Rear Air/Fuel Ratio (A/F) Sensor (Bank 1, Sensor 1) VS Line High Voltage
P2252: Air/Fuel Ratio (A/F) Sensor (Sensor 1) AFS- Line Low Voltage
P2254: Front Air/Fuel Ratio (A/F) Sensor (Bank 2, Sensor 1) VS Line High Voltage
P2255: Front Air/Fuel Ratio (A/F) Sensor (Bank 2, Sensor 1) VS Line Low Voltage
P2279: Intake Air System Leak
P2413: Exhaust Gas Recirculation (EGR) System Range/Performance Problem
P2422: Evaporative Emission (EVAP) System Vent Shut Valve Close Malfunction
P2552: Throttle Actuator Control Module Relay Malfunction
P2627: Rear Air/Fuel Ratio (A/F) Sensor (Bank 1, Sensor 1) LABEL Circuit Low Voltage
P2628: Rear Air/Fuel Ratio (A/F) Sensor (Bank 1, Sensor 1) LABEL Circuit High Voltage
P2630: Front Air/Fuel Ratio (A/F) Sensor (Bank 2, Sensor 1) LABEL Circuit Low Voltage
P2631: Front Air/Fuel Ratio (A/F) Sensor (Bank 2, Sensor 1) LABEL Circuit High Voltage
P2646: VTEC Oil Pressure Switch Circuit Low Voltage
P2647: VTEC Oil Pressure Switch Circuit High Voltage
P2648: VTEC Solenoid Valve Circuit Low Voltage
P2649: VTEC Solenoid Valve Circuit High Voltage
P2769: Short in Torque Converter Clutch Solenoid Valve Circuit
P2770: Open in Torque Converter Clutch Solenoid Valve Circuit
P2A00: Air/Fuel Ratio (A/F) Sensor (Sensor 1) Range/Performance Problem
P2A03: Front A/F Sensor Circuit (Bank 2, Sensor 1) Circuit Range/Performance Problem
U0073: FCAN Malfunction (Bus-off)
U0107: Lost Communication With Throttle Actuator Control Module
U0121: FCAN Malfunction (TCS-PCM)
U0155: FCAN Malfunction (Gauge Control Module-ECM/PCM)

This list provides a starting point for understanding common Honda OBD2 codes. Remember that this is not an exhaustive list, and specific codes may vary slightly depending on your Honda model and year.

What to Do After Retrieving Honda ECU Codes

Once you have your Honda ECU codes, the next crucial step is interpretation and action.

Research the Codes: Use the provided lists and online resources to understand what each code signifies. Websites like OBD-Codes.com or reputable automotive forums can be helpful.
Consider Code Severity: Some codes indicate minor issues (like a loose gas cap), while others point to serious problems (like engine misfires or catalytic converter failure). Prioritize addressing critical codes first.
Basic Troubleshooting: For simple codes, you might be able to perform basic troubleshooting yourself. For example, for an EVAP code (like P0457), check your gas cap. For a MAF sensor code (like P0101), inspect the sensor and its wiring.
Wiring Diagrams and ECU Pinouts: For more in-depth diagnostics, especially for older OBD1 systems or when dealing with sensor circuit issues, wiring diagrams are invaluable. The following diagrams show ECU pinouts and wire colors for 92-95 Honda Civics, which can be helpful for tracing circuits and testing components.

Alt text: Wiring diagram for a 1992-1995 Honda Civic ECU, detailing wire colors and pin functions.

Key to Wiring Diagram:
- (Wire color): Indicates the wire color (e.g., Wht = White, Blk = Black).
- (Function/Description (if need be)): Describes the wire’s function, if necessary.
- (Voltage Value (DC Volts Unless otherwise specified) V = Volts): Specifies voltage values for testing (KOEO = Key On Engine Off, KOER = Key On Engine Running).
Alt text: Diagram of the OBD1 shock tower plug connector in a Honda vehicle, showing pin locations.

Alt text: Diagram illustrating the use of a pin removal tool for Honda OBD1 connectors.
Consult a Professional Mechanic: For complex issues, or if you are uncomfortable working on your car yourself, it’s always best to consult a qualified mechanic. Provide them with the ECU codes you retrieved; this will significantly speed up the diagnostic process and potentially save you money.

Conclusion

Understanding Honda ECU codes is a valuable skill for any car owner. By learning how to retrieve and interpret these codes, you can gain insights into your vehicle’s health, perform basic troubleshooting, and communicate effectively with automotive professionals. Whether you drive a classic OBD1 Honda or a modern OBD2 model, this guide provides the foundational knowledge to decode your Honda’s diagnostic messages and keep your car running smoothly. Remember to always prioritize safety and consult a professional when dealing with complex automotive issues.