Decoding Your Honda Check Engine Light: OBD2 Codes Explained

Navigating the world of car repairs can be daunting, especially when that ominous Check Engine Light (CEL) pops up on your Honda’s dashboard. Terms like OBD2, DTC codes, and MIL can feel like a foreign language. If you’re like many Honda owners and find yourself confused by these lights and codes, you’ve come to the right place. This guide is designed to demystify the Honda Check Engine Light Codes Obd2 system, empowering you to understand what’s happening under the hood of your car and take informed action.

Understanding OBD-II and Your Honda

Let’s start with the basics: What exactly is OBD-II? OBD-II, or On-Board Diagnostics II, is a standardized system implemented in all cars manufactured in 1996 and later in the United States. Think of it as a universal translator for your car’s computer. Before OBD-II, each car manufacturer had their own proprietary diagnostic systems. Reading trouble codes often involved complex procedures, like counting blinks from the check engine light in a specific sequence, and the codes themselves varied between makes and models.

OBD-II changed all of that. It standardized:

• Diagnostic Trouble Codes (DTCs): A uniform set of codes that identify specific problems within your vehicle.
• Data Port Connector: A standard 16-pin connector, typically located under the driver’s side dashboard, making it easily accessible for code readers and scanners.
• Communication Protocols: Standardized ways for diagnostic tools to communicate with your car’s computer (Engine Control Module or ECM).

This standardization means that regardless of the car brand (including Honda), a generic OBD2 scanner can be used to retrieve diagnostic information. This is a huge advantage for both car owners and mechanics, simplifying diagnostics and repairs.

Is a Check Engine Light Always Serious in a Honda?

Not necessarily. The Check Engine Light (CEL), also sometimes referred to as the Malfunction Indicator Lamp (MIL), is designed to alert you to potential issues. However, the severity of these issues can vary greatly. The OBD-II system is primarily focused on monitoring components that affect vehicle emissions. Therefore, many CEL triggers relate to emission control systems.

For example, a faulty oxygen sensor located after the catalytic converter might trigger the CEL. While this sensor is crucial for monitoring emissions system efficiency, it doesn’t directly impact engine performance in terms of power, fuel delivery, or spark. In this case, your Honda might still drive normally, but the CEL is illuminated to indicate a potential emissions problem.

Conversely, some engine faults that do impact performance might not immediately trigger the CEL, or might require the fault to occur multiple times before the light comes on. The system isn’t perfect, and it’s always best to investigate a lit CEL rather than ignore it.

Honda “Limp Home” Mode and OBD-II

One of the significant benefits of OBD-II is its contribution to vehicle reliability through what’s often called “limp home” mode, or reduced power mode. In older cars, a sensor malfunction could lead to serious driveability issues, or even engine stalling. OBD-II equipped Hondas, however, are designed to be more resilient.

If a critical sensor fails, the Honda ECM will often enter a “limp home” mode. This mode allows you to continue driving the car (often with reduced power and functionality) to a safe location or repair shop, preventing a complete breakdown.

Here’s how it works with some common sensor failures in Hondas:

• Mass Air Flow (MAF) Sensor Disconnected: Instead of stalling, the ECM will use data from other sensors like RPM, throttle position, and Manifold Absolute Pressure (MAP) sensor to estimate airflow and keep the engine running.
• Coolant Temperature Sensor Failure: If the coolant temperature sensor gives an implausible reading (e.g., suddenly drops from hot to extremely cold), the ECM will recognize the fault and use a default coolant temperature value (like 176°F/80°C) for fuel and spark calculations.
• Excessive Cylinder Misfire: If the ECM detects excessive misfires in a cylinder (which can damage the catalytic converter due to unburnt fuel), it can temporarily shut off the fuel injector to that cylinder to prevent further damage.

While “limp home” mode is a valuable safety feature, it’s not a long-term solution. It indicates a problem that needs attention, and driving in limp mode for extended periods can potentially cause further issues.

Can Modifications Trigger Honda Check Engine Lights?

Yes, aftermarket modifications, especially those affecting the engine or emissions systems, can trigger the check engine light on your Honda.

• Exhaust Modifications: Some aftermarket exhaust systems, particularly downpipes that remove or relocate the catalytic converter, can cause CELs. This is often because the catalytic converter isn’t heating up sufficiently to operate efficiently, or because oxygen sensor placement is altered.
• Sensor Manipulation: Modifying or tampering with sensor data is almost guaranteed to cause problems with the OBD-II system and trigger CELs. The system is designed to detect inconsistencies and out-of-range sensor readings.

Generally, well-designed “bolt-on” performance parts like cat-back exhaust systems are less likely to cause issues. However, any modification that changes sensor readings or affects emissions control components can potentially lead to a check engine light.

Decoding Honda OBD2 Trouble Codes

OBD2 trouble codes, also known as Diagnostic Trouble Codes (DTCs), are five-digit alphanumeric codes. Understanding the structure of these codes can be helpful:

• First Character (Letter): Indicates the system where the fault occurred:
  • P: Powertrain (Engine, Transmission)
  • C: Chassis (Brakes, Suspension, Steering)
  • B: Body (Body Control Modules, Interior)
  • U: Network/Communication (Communication bus systems)
• Second Character (Digit): Indicates if the code is generic (standardized across all manufacturers) or manufacturer-specific:
  • 0: Generic OBD-II code
  • 1, 2, or 3: Manufacturer-specific code
• Third Character (Digit): Indicates the specific vehicle subsystem:
  • 0: Fuel and Air Metering
  • 1: Fuel and Air Metering (Injector Circuit)
  • 2: Fuel and Air Metering (Injector Circuit)
  • 3: Ignition System or Misfire
  • 4: Auxiliary Emission Controls
  • 5: Vehicle Speed Controls and Idle Control System
  • 6: Computer Output Circuit
  • 7: Transmission
  • 8: Transmission
  • 9: Transmission
  • (and more)
• Fourth and Fifth Characters (Digits): Specific fault number within the subsystem.

For example, P0115 translates to:

• P: Powertrain
• 0: Generic OBD-II code
• 1: Fuel and Air Metering
• 15: Specific fault number – related to the Engine Coolant Temperature (ECT) circuit.

The full description for P0115 is “Engine Coolant Temperature Circuit Malfunction.” There can be multiple codes for a single sensor (e.g., P0116 – “Engine Coolant Temperature Circuit Range/Performance Problem”). This detailed coding system helps pinpoint the exact nature of the problem.

It’s also important to note that sometimes a single faulty component can trigger multiple DTCs. For instance, a failing oxygen sensor might result in codes like P0130, P0131, and P0133. In such cases, addressing the root cause (replacing the faulty sensor) can resolve all related codes.

Common Honda OBD2 Check Engine Light Codes

Here’s a compilation of common Honda OBD2 codes. This list includes both OBD-II codes and their corresponding CEL codes (older Honda specific codes, where applicable). While OBD2 scanners provide the ‘P’ codes, older Honda diagnostic methods might display the CEL codes. Understanding both can be helpful.

MIL/CEL Code	OBDII Code	Description of Code
1	P0131	Primary HO2S Circuit Low Voltage (Sensor 1)
1	P0132	Primary HO2S Circuit High Voltage (Sensor 1)
3	P0107	MAP Circuit Low Input
3	P0108	MAP Circuit High Input
4	P0335	CKP Sensor Circuit Low Input
4	P0336	CKP Sensor Range/Performance
5	P0106	MAP Circuit Range Or Performance
5	P1128	MAP Lower Than Expected
5	P1129	MAP Higher Than Expected
6	P0117	ECT Circuit Low Input
6	P0118	ECT Circuit High Input
7	P0122	TP Sensor Circuit Low Input
7	P0123	TP Sensor Circuit High Input
7	P1121	Throttle Position Lower Than Expected
7	P1122	Throttle Position Higher Than Expected
8	P1359	CKP/TDC Sensor Connector Disconnection
8	P1361	TDC Sensor Intermittent Interruption
8	P1362	TDC Sensor No Signal
9	P1381	Cylinder Position Sensor Intermittent Interruption
9	P1382	Cylinder Position Sensor No Signal
10	P0111	IAT Sensor Circuit Range/Performance
10	P0112	IAT Sensor Circuit Low Input
10	P0113	IAT Sensor Circuit High Input
12	P1491	EGR Valve Lift Insufficient Detected
12	P1498	EGR Valve Lift Sensor High Voltage
13	P1106	BARO Circuit Range/Performance
13	P1107	BARO Circuit Low Input
13	P1108	BARO Circuit High Input
14	P0505	ICS Malfunction
14	P1508	IAC Valve Circuit Failure
14	P1509	IAC Valve Circuit Failure
14	P1519	Idle Air Control Valve Circuit Failure
17	P0500	VSS Circuit Malfunction (M/T)
17	P0501	VSS Circuit Range/Performance (A/T)
20	P1297	Electrical Load Detector Circuit Low Input
20	P1298	Electrical Load Detector Circuit High Input
21	P1253	VTEC System Malfunction
22	P1257, P1258, P1259	VTEC System Malfunction
23	P0325	KS Circuit Malfunction
30	P1655	SEAF/SEFA/TMA/TMB Signal Line Failure
30	P1681	A/T FI Signal A Low Input
30	P1682	A/T FI Signal A High Input
31	P1686	A/T FI Signal B Low Input
31	P1687	A/T FI Signal B High Input
34	P0560	Powertrain Control Module (PCM) Backup Voltage Circuit Low Voltage
41	P0135	Front HO2S Heater Circuit Fault (Sensor 1)
41	P1166	Primary HO2S (No. 1) Heater System Electrical
41	P1167	Primary HO2S (No. 1) Heater System
45	P0171	System Too Lean
45	P0172	System Too Rich
48	P1162	Primary HO2S (No. 1) Circuit Malfunction
48	P1168	Primary HO2S (No. 1) LABEL Low Input
48	P1169	Primary HO2S (No. 1) LABEL High Input
54	P1336	CSF Sensor Intermittent Interruption
54	P1337	CSF Sensor No Signal
58	P1366	TDC Sensor No. 2 Intermittent Interruption
58	P1367	TDC Sensor No 2 Signal
61	P0133	Primary HO2S Circuit Slow Response (Sensor 1)
61	P1149	Primary HO2S (Sensor 1) Circuit Range/Performance Problem
61	P1163	Primary HO2S (No. 1) Circuit Slow Response
61	P1164	Primary HO2S (No. 1) Circuit Range/Performance
61	P1165	Primary HO2S (No. 1) Circuit Range/Performance
63	P0137	Secondary HO2S Circuit Low Voltage (Sensor 2)
63	P0138	Secondary HO2S Circuit High Voltage (Sensor 2)
63	P0139	Secondary HO2S Circuit Slow Response (Sensor 2)
65	P0141	Secondary HO2S Heater Circuit Fault (Sensor 2)
67	P0420	Catalyst System Efficiency Below Threshold
70	P0700, P0715, P0720, P0725, P0730, P0740, P0753, P0758, P0763, P0780, P1660, P1705, P1706, P1738, P1739, P1753, P1758, P1768, P1773, P1785, P1786, P1790, P1791, P1792, P1793, P1794, P1870, P1873, P1879, P1885, P1886, P1888, P1890, P1891	A/T Concerns
71	P0301	Misfire Cyl. 1 Or Random Misfire
72	P0302	Misfire Cyl. 2 Or Random Misfire
73	P0303	Misfire Cyl. 3 Or Random Misfire
74	P0304	Misfire Cyl. 4 Or Random Misfire
75	P0305	Misfire Cyl. 5 Or Random Misfire
76	P0306	Misfire Cyl. 6 Or Random Misfire
80	P0401	EGR Insufficient Flow Detected
86	P0116	ECT Circuit Range Or Performance
90	P1456	EVAP Emission Control System Leak Detected (Fuel Tank System)
90	P1457	EVAP Emission Control System Leak Detected (Control Canister System)
91	P0451	Fuel Tank Pressure Sensor Range/Performance
91	P0452	Fuel Tank Pressure Sensor Circuit Low Input
91	P0453	Fuel Tank Pressure Sensor Circuit High Input
92	P0441	EVAP Emission Control System Improper Purge Flow
92	P1459	EVAP Emission Purge Flow Switch Malfunction
—	P0300	Random Misfire
—	P1486	Thermostat Range/Performance Problem
—	P1607	ECM/PCM Internal Circuit Failure A
—	P1676	FPTDR Signal Line Failure
—	P1678	FPTDR Signal Line Failure
71–74	P1300	Multiple Cylinder Misfire Detected

Reading Honda OBD2 Codes: Scanner vs. Paperclip Method (Older Models)

For modern Hondas (generally post-1996), the easiest way to read OBD2 codes is by using an OBD2 scanner. These scanners range from basic handheld devices to more advanced professional-grade tools. They plug directly into the OBD2 port (usually under the dash) and can retrieve the stored DTCs.

Using an OBD2 Scanner:

1. Locate the OBD2 port: It’s typically under the driver’s side dashboard.
2. Plug in the scanner: Turn the ignition to the “ON” position (do not start the engine).
3. Follow scanner instructions: Most scanners have a “Read Codes” or similar function.
4. Record the codes: Write down any retrieved DTCs.
5. Consult a code definition resource: Use online resources or the scanner’s manual to understand what each code means.

The “Paperclip Method” (For some older Hondas):

For some older Honda models (pre-OBD2 standardization, or early OBD2 implementations), a paperclip method can be used to retrieve basic CEL codes. However, this method is not universally applicable to all Hondas, and it’s generally recommended to use an OBD2 scanner for accuracy and comprehensive diagnostics.

Disclaimer: Using the paperclip method incorrectly can potentially damage your vehicle’s electrical system. Proceed with caution and ensure you are following instructions specific to your Honda model and year.

If you choose to attempt the paperclip method (for older Hondas, and with caution):

1. Locate the OBD2 connector: It’s usually under the driver’s side dash.
2. Identify the correct pins: Consult your Honda service manual or reliable online resources to identify the specific pins for your model and year that need to be jumped. Incorrect pins can cause damage.
3. Insert a paperclip: Carefully insert a paperclip to bridge the designated pins.
4. Turn the ignition to “ON”: (Do not start the engine).
5. Observe the Check Engine Light: The CEL will blink in a pattern. Long blinks represent “10” and short blinks represent “1”. Count the blinks to decode the code. For example, one long blink followed by three short blinks would be code 13.
6. Consult a Honda CEL code chart: Use a chart specific to your older Honda model to interpret the CEL codes.

Example of an OBD2 connector location under the dash.

Example of paperclip insertion for code reading (older system, verify for your specific model).

Another example of paperclip insertion (older system, verify for your specific model).

What To Do After Retrieving Honda OBD2 Codes

Once you have retrieved the Honda check engine light codes OBD2, the next step is to diagnose and address the underlying issue.

1. Research the Codes: Use the code descriptions in the table above or reliable online OBD2 code resources to understand what each code signifies.
2. Basic Troubleshooting: For some codes, simple checks can be performed:
   • Loose gas cap: For EVAP system codes (P044x, P145x), check and tighten your gas cap.
   • Sensor connections: Visually inspect sensor connectors related to the code for looseness or damage.
3. Prioritize Codes: Some codes are more critical than others. Codes related to engine misfires, fuel delivery, or critical sensors should be addressed promptly.
4. Consider Professional Help: If you are not comfortable diagnosing or repairing car issues yourself, or if the codes indicate a complex problem, it’s best to consult a qualified mechanic, especially a Honda specialist.
5. Don’t Ignore the CEL: Even if your car seems to be driving normally, a lit CEL indicates a problem that could worsen over time or lead to more serious damage. Addressing issues early can save you money and prevent breakdowns.

Conclusion

Understanding Honda check engine light codes OBD2 is a valuable skill for any Honda owner. While the check engine light can be initially alarming, with a little knowledge and the right tools (like an OBD2 scanner), you can decipher the codes, understand the potential issues, and take informed steps towards resolving them. Remember to prioritize safety, research codes thoroughly, and don’t hesitate to seek professional help when needed. By being proactive and informed, you can keep your Honda running smoothly and efficiently for years to come.