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P39 OBD1 ECU Technical Reference

Technical reference for the P39 OBD1 ECU found in 1992-1995 JDM Honda Prelude BB4 models equipped with the F22B DOHC non-VTEC engine.

Updated June 19, 2026 Intermediate 3

kabuki Author

carotman Author

The P39 is an OBD1 engine control unit (ECU) utilized in 1992â1995 JDM Honda Prelude (BB4) chassis vehicles equipped with the F22B DOHC non-VTEC engine.

ECU Overview

The P39 is typically found in automatic transmission configurations. Hardware modifications are required to convert the unit for manual transmission operation.

Resistor close up — Resistor close-up on P39 automatic ECU

Side profile of P39 Spoon automatic ECU

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Transmission Conversion

To convert an automatic P39 ECU for use with a manual transmission, the following hardware modification is required:

Important

Moving the resistor from the RP11 position to the RP12 position is necessary to signal the ECU to operate in manual transmission mode.

<figure> <img src="ecu2_936.jpg" alt="Auto P39 ECU converted to Manual"> <figcaption>Automatic P39 ECU converted to manual by relocating resistor from RP11 to RP12</figcaption> </figure>

Applies to

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Honda

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Model Prelude