Honda Ecu 3.5.5.2 Page

To identify if you have this firmware, you need to read the backup EPROM or use a diagnostic scanner to request the calibration ID. However, based on Honda’s technical service bulletins, the most common hardware carrying 3.5.5.2 is:

| Honda Part Number | Vehicle Model | Engine | OBD Type | |-------------------|---------------|--------|----------| | 37820-P2E-A51 | 1999-2000 Civic EX | D16Y8 | OBD2B | | 37820-P75-A51 | 1998-2001 Integra LS | B18B1 | OBD2B | | 37820-P2P-A51 | 1997-1998 Civic Si | B16A2 | OBD2A | honda ecu 3.5.5.2

Note: The "A51" suffix often correlates with the 3.5.5.2 software stack. If you see "A52" or "A53," that usually indicates a newer emissions recall update. To identify if you have this firmware, you

✅ More reliable for 2010–2020 models
✅ Resolves “communication error” on many newer ECUs
✅ Free update if you have a valid i-HDS subscription ✅ More reliable for 2010–2020 models ✅ Resolves

Unlike the crude OBD1 ECUs, the 3.5.5.2 firmware uses adaptive closed-loop fueling with a wideband-like narrowband O2 sensor strategy. The ECU learns long-term fuel trims (LTFT) and short-term fuel trims (STFT) more accurately. For a naturally aspirated build (I/H/E), this ECU actually runs smoother than a chipped P28.