USDM and JDM OBD1 Honda ECUs (e.g., P28, P30, P72, P06) share common hardware board layouts for both automatic and manual configurations. You can convert an automatic ECU for use in a manual transmission vehicle by modifying specific surface-mount resistor locations (RP17 and RP18).

Technical Overview#

The ECU determines its transmission configuration by measuring resistance across two specific board locations: RP17 and RP18.

• Automatic Configuration: Detected by the MCU via resistance on both RP17 and RP18. Running an automatic ECU in a manual car without this conversion will trigger Diagnostic Trouble Code 19 (Automatic Transmission Lockup Solenoid).
• Manual Configuration: Achieved by jumpering RP18 and leaving RP17 empty, forcing the MCU to ignore automatic transmission control logic.

Conversion Procedures#

1. USDM Automatic to Manual#

1. Locate RP17 and RP18 on the lower right corner of the ECU circuit board.
2. De-solder and remove both existing resistors.
3. Install a solid jumper wire (or 0-Ohm resistor) in the RP18 position.
4. Leave the RP17 position empty (open).

2. JDM Automatic to Manual#

JDM small-case and large-case ECUs utilize a single resistor location for transmission configuration.

1. Locate RP18 on the back side of the board.
2. De-solder and remove the factory 2.4k Ohm resistor.
3. Install a 1.4k Ohm resistor in its place.

3. USDM Manual to Automatic#

If converting a manual ECU for automatic transmission support:

1. Remove the RP18 jumper.
2. Install a 2.7k Ohm resistor at RP18.
3. Install a 4.7k Ohm resistor at RP17.
4. Note: You must also ensure the transmission solenoid driver transistor array (IC16, typically a 5050S chip) is installed on the board.

Technical Note#

Always verify your specific ECU part number, production region, and circuit board markings before soldering. Incorrect resistor values or improperly bridged pads can result in ECU failure or engine mismanagement.