OBD1 Honda P30 ECU Reference Guide
A complete hardware and software reference guide for the JDM and USDM OBD1 P30 DOHC VTEC ECU, including RAM and ROM memory mapping.
The P30 Engine Control Unit (ECU) is a primary OBD1 Honda ECU. Originally equipped in 1992â1995 Honda Civic SiR/SiR-II (JDM) and Del Sol VTEC (USDM/JDM) models with the DOHC VTEC B16A engine, it serves as a foundational codebase for custom Honda tuning systems.
Overview
The P30 contains native code routines for DOHC VTEC operation and knock sensing. Its ROM structure (specifically the JDM J11 board with 203 ROM code) is the baseline for many tuning platforms. This guide maps critical memory addresses for both RAM (runtime values) and ROM (EEPROM calibration parameters).
Board Identification & Variations
- JDM Small Case: Utilizes an external ROM board socketed directly from the factory.
- USDM Big Case: Standard form-factor; requires socketing to add external EEPROMs.
- EDM Big Case (P30-G01): Sourced from the UK-spec Civic VTi; utilizes an internal ROM chip with available solder pads for external EEPROM mounting.
ECU Connector Pin References
When verifying inputs and wiring, all ECU connector pin references must conform to the standard OBD1 Honda pinout mapping. Refer to the OBD1 ECU pinout schematics0 for details.
RAM Address Mapping
The following table outlines memory addresses used for datalogging, diagnostics, and sensor feedback.
| Location | Bytes | Description | Notes |
|---|---|---|---|
| 00A3 | 1 | MAP Sensor | Manifold Absolute Pressure analog input (0V-5V) |
| 00A4 | 1 | PA Sensor | Barometric Pressure sensor |
| 00AC | 2 | Current RPM | Engine speed (OBD1 16-bit) |
| 00B4 | 1 | VSS Sensor | Vehicle Speed Sensor (km/h) |
| 00B8 | 1 | Current TPS | Throttle Position Sensor (0V-5V) |
| 00C0 | 1 | IAT Sensor | Intake Air Temperature |
| 00C1 | 1 | ECT Sensor | Engine Coolant Temperature |
| 011F.1 | 1b | VTEC Flag Active | Status flag for fuel/ignition map switching |
| 0211.1 | 1b | VTEC Pressure Switch | 0 if grounded (active pressure) |
| 0222.1 | 1b | VTEC Solenoid Output | VTEC solenoid power relay control (VTS) |
ROM Address Mapping
These hex address offsets apply to the 28-pin EEPROM chip for the standard P30 203 JDM codebase.
| Location | Bytes | Description | Notes |
|---|---|---|---|
| 11B6 | 1 | VTP/VTS Error Removal | Set to 0x30 to bypass VTEC pressure/solenoid checks |
| 1831 | 1 | Speed Limiter | 0xB9 = 180 km/h; 0xFE = 254 km/h |
| 2B75 | 2 | Target Idle RPM | Little-endian 16-bit RPM format |
| 6001 | 1 | VTEC System Enable | 0xFF enables, 0x00 disables |
| 6002 | 1 | Knock Sensor Enable | 0xFF enables, 0x00 disables |
| 6387 | 2 | High Cam RPM Cut | Ignition cut limit (high cam/VTEC) |
| 7032 | 200 | Low Cam Fuel Table | 10x20 base fueling lookup map |
| 7104 | 200 | High Cam Fuel Table | 10x20 VTEC fueling lookup map |
| 724E | 200 | Low Cam Ignition Map | 10x20 low cam ignition advance |
| 7316 | 200 | High Cam Ignition Map | 10x20 VTEC ignition advance |
Important
Modifying ROM addresses requires a verified checksum calculation. Failure to update the checksum after editing will result in a "Check Engine Light" (CEL) and potential limp-mode operation.
Tip
Use the
600xseries addresses to quickly toggle diagnostic routines (e.g., O2 heater, Baro sensor) when running non-stock engine configurations.