P29 OBD1 ECU Technical Reference
Technical reference for the P29 OBD1 ECU, commonly found in JDM Honda Domani and Civic 25th Anniversary models equipped with the DOHC ZC engine.
The P29 ECU is an OBD1 engine control unit utilized in Japanese Domestic Market (JDM) Honda Domani and Civic 25th Anniversary models. It is specifically calibrated for the DOHC ZC engine platform.
Overview
The P29 shares the standard OBD1 architecture common to the 1992â1995 Honda Civic/Integra chassis. It is frequently sought after for its specific fuel and ignition maps tailored to the DOHC ZC engine.
Note
Ensure your engine harness matches the standard OBD1 pinout configuration before installation.
ECU Specifications
- Generation: OBD1
- Market: JDM (Japanese Domestic Market)
- Engine Application: DOHC ZC
- Chassis Application: Domani / Civic 25th Anniversary
Diagnostic Support
Use the following tool to cross-reference error codes associated with this ECU platform:
Compatibility
The P29 is physically and electrically compatible with standard 1992â1995 Honda OBD1 engine harnesses.
Important
While the ECU is plug-and-play for most OBD1 chassis, verify that your specific engine sensor suite (e.g., O2 sensor type, knock sensor presence) matches the requirements of the P29 calibration to avoid Check Engine Light (CEL) triggers.
Resistor Color Code Reference
Use the color bands on through-hole resistors to identify their resistance value before installing ECU jumpers, pull-ups, voltage dividers, or sensor-scaling parts.
How to Read the Bands
| Resistor Type | Band 1 | Band 2 | Band 3 | Band 4 | Band 5 |
|---|---|---|---|---|---|
| 4-band | 1st digit | 2nd digit | Multiplier | Tolerance | - |
| 5-band | 1st digit | 2nd digit | 3rd digit | Multiplier | Tolerance |
Color Values
| Color | Digit | Multiplier | Tolerance |
|---|---|---|---|
| Black | 0 | x1 | - |
| Brown | 1 | x10 | +/- 1% |
| Red | 2 | x100 | +/- 2% |
| Orange | 3 | x1,000 | - |
| Yellow | 4 | x10,000 | - |
| Green | 5 | x100,000 | +/- 0.5% |
| Blue | 6 | x1,000,000 | +/- 0.25% |
| Violet | 7 | x10,000,000 | +/- 0.1% |
| Gray | 8 | x100,000,000 | +/- 0.05% |
| White | 9 | x1,000,000,000 | - |
| Gold | - | x0.1 | +/- 5% |
| Silver | - | x0.01 | +/- 10% |
| No band | - | - | +/- 20% |
Common ECU Examples
| Value | 4-Band Code | Typical Use |
|---|---|---|
| 220 ohm | Red, Red, Brown, Gold | LED/current-limiting or ECU hardware mods |
| 1k ohm | Brown, Black, Red, Gold | Pull-up, jumper, and driver-bias circuits |
| 1.2k ohm | Brown, Red, Red, Gold | Driver-bias circuits such as IACV repair references |
| 4.7k ohm | Yellow, Violet, Red, Gold | Transistor base resistor circuits |
| 10k ohm | Brown, Black, Orange, Gold | Pull-up, pull-down, and sensor-divider circuits |
Tip
Always confirm the measured value with a multimeter before soldering. Old ECU resistors can be heat-discolored, and some boards use small surface-mount parts marked with numeric codes instead of color bands.