Understanding your Honda Engine Control Unit (ECU) is crucial for diagnostics, repairs, and upgrades. Specifically, identifying whether your P75 ECU is OBD1 or OBD2 is a common point of interest for Honda and Acura enthusiasts. This guide will walk you through how to easily identify your ECU type by examining the identification label and connectors, focusing on the P75 ECU and the differences between OBD1 and OBD2 systems.
The ECU’s identification sticker holds key information about your unit. Let’s break down how to read it:
Alt text: Honda ECU identification sticker showing model number 37820, ECU code P75, and revision number.
Reading the ECU Identification Label
There are three main sections to understand on the ECU identification sticker:
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A. Model Number (37820): This number, 37820, is consistent across all Honda ECUs, regardless of the model (Integra, Civic, Accord, etc.). It’s the universal Honda ECU model prefix and will always be the first number you see on the sticker.
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B. Model and Year Code (P75): This is the most important part for identification. The code P75 specifically indicates the ECU model. For Integra models, P75 ECUs are typically associated with LS/RS trims. Crucially, the P75 code can be found on both OBD1 and OBD2 ECUs depending on the year of the vehicle. We’ll clarify how to differentiate between OBD1 and OBD2 P75 ECUs shortly.
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C. Revision Number (e.g., -A01, -A04): The revision number, such as -A01 or -A04, indicates different versions of the same ECU model. As seen in the example, a P75-A01 might come from an older vehicle (like a 94 LS), while a P75-A04 could be from a newer one (like a 98 LS). Honda has stated that revisions often represent upgrades to the ECU’s motherboard or chips, potentially due to evolving emissions standards or other enhancements. It’s important to note that the core ECU code (like P75) remains, but the revision reflects internal changes.
Integra ECU Codes and OBD Generations
Here’s a list of common ECU codes found in USDM Integras to provide context, highlighting the P75 and its OBD variations:
- P61: 92-93 OBD1 GSR
- P72: 94-95 OBD1 GSR
- P72: 96-00 OBD2 GSR
- P73: 96-00 OBD2 ITR
- P74/P75: 92-95 OBD1 LS/RS
- P75: 96-00 OBD2 LS/RS
- PG6: 88-89 OBD0 (all models)
- PR4: 90-91 OBD0 LS/GS
- PR4: 92-93 OBD1 LS/GS
As you can see, the P75 ECU appears in both OBD1 (92-95) and OBD2 (96-00) generations. Therefore, relying solely on the P75 code isn’t enough to determine the OBD type. You need to examine the ECU connectors.
Distinguishing OBD1, OBD2a, and OBD2b ECUs by Connectors
The most definitive way to differentiate between OBD1 and OBD2 ECUs, including variations like OBD2a and OBD2b, is by looking at the ECU connectors on the back of the unit.
Alt text: Image comparing OBD1 ECU connectors with three plugs to OBD2a ECU connectors with four plugs, highlighting plug arrangement differences.
Connector Count and Arrangement:
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OBD1 ECU: OBD1 ECUs will have three connectors or receptacles on the back. This is the most significant visual difference.
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OBD2 ECU (OBD2a and OBD2b): OBD2 ECUs will have four connectors. However, it’s important to note that one of these four slots is not always used.
OBD2a vs OBD2b Connector Order:
While both OBD2a and OBD2b ECUs have four connector slots, the key difference lies in the order of the plugs:
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OBD2a: Typically, the first connector slot is used, the second is skipped (empty), and the remaining two are used.
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OBD2b: On OBD2b ECUs, the first three connector slots are used, and the last one is skipped.
OBD0 ECUs: OBD0 ECUs are easily distinguishable from both OBD1 and OBD2 due to their completely different connector style. OBD0 ECUs typically feature a green plug, a metal partition, and then two black plugs, a different configuration altogether.
Why OBD Identification Matters
Knowing whether your P75 ECU is OBD1 or OBD2 is critical, especially if you are considering an ECU conversion or engine management modifications. Using the wrong ECU type for your vehicle’s wiring harness will lead to malfunctions and the system simply will not work. OBD2b ECUs were generally introduced in later model year Integras (around 1999 and up), so this distinction is particularly important for vehicles in that range.
By examining the ECU label and, more importantly, the number and arrangement of the connectors, you can confidently identify whether you have a P75 OBD1 or OBD2 ECU and ensure compatibility for any modifications or repairs.
