The P14 ECU was used by Honda in the 1993–1995 OBD1 Prelude Si (USDM B23A1/H23A1 DOHC non-VTEC engine). It is a highly robust platform, though there are several distinct internal board revisions that tuners must be aware of when socketing or modifying the board.

1. Board Variants & Knock Sensor Configurations#

The P14 board exists in at least two major configurations depending on whether the vehicle was equipped with an active knock sensor system:

• Knock-Equipped Boards: These revisions populate the knock processing daughterboard slot. The supporting resistor pads at R118, R119, and R101 are populated from the factory.
• Knockless Boards: These boards lack the knock daughterboard. Instead of the default locations, resistors R118 and R119 are relocated to pads R142 and R143.

Note: If you are modifying a knock-equipped board to bypass the sensor check, refer to the Knock Sensor Removal / Bypass guide.

2. Factory External ROM vs. Romless Boards#

While most USDM OBD1 ECUs require adding a logic latch (74HC373) and jumper (J1) to accept an external ROM, some P14 models (particularly JDM and European knock-equipped revisions) were manufactured with an external ROM from the factory.

Comparing the factory external ROM board with the standard romless board reveals that the external ROM board is missing resistor R15.

3. Board Layout Reference Images#

Below are circuit board reference images for the major P14 configurations:

USDM Prelude Si P14-A10 (Manual Transmission)#

This is the standard USDM manual transmission board layout:

Internal view of the USDM P14-A10 manual transmission board.

Exterior case labeling of the USDM P14-A10 ECU.

USDM P14-A00 (4WS and Knock Sensor)#

Revisions equipped with active Four-Wheel Steering (4WS) and a knock board:

High-resolution shot of the P14-A00 board with 4WS and knock processing circuitry.

Detail view of the knock processing daughterboard installed on the P14-A00.

European and Alternate Revisions#

European market P14 manual board layout lacking the knock daughterboard.

Alternate P14 board layout populated with a factory external ROM and knock daughterboard.

4. Archived Files & Downloads#

For tuning and analysis, you can download the stock ROM image extracted from the factory external ROM version of the P14:

• Download the archived P14 Knock ROM BIN (32 KB, Stock H23A calibration)