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OBD1 Civic/Integra Auto to Manual Conversion

Convert USDM and JDM OBD1 Civic/Integra ECUs between automatic and manual configurations by changing resistor board values.

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Adapted from pgmfi.org wiki

USDM and JDM OBD1 Honda ECUs (such as the P28, P30, P72, and P06) share almost identical hardware boards for both automatic and manual transmission cars. You can convert these ECUs between automatic and manual configurations by modifying a few surface-mount resistors (RP17 and RP18).

Overview

The ECU checks the electrical resistance at locations RP17 and RP18 to determine if it should look for an automatic transmission control system or operate as a manual ECU.

  • If configured as an automatic ECU on a manual car, the ECU will throw a Code 19 (Automatic Transmission Lockup Control Solenoid) and may hold a slightly erratic idle.
  • Converting the board to manual tells the MCU to ignore the automatic transmission solenoids.

OBD1 automatic vs manual jumper board locations OBD1 ECU board layout. The jumper configuration is located in the lower right, alongside the transmission transistor circuits.

Specifications

USDM Resistor Values (RP17 & RP18)

Jumper/Resistor Location Automatic Manual
RP17 4.7k Ohm Open (Removed)
RP18 2.7k Ohm Jumpered (0 Ohm wire)

JDM Resistor Values (RP18 Only)

Jumper/Resistor Location Automatic Manual
RP18 2.4k Ohm 1.4k Ohm

Procedure

USDM Automatic to Manual Conversion

To convert a USDM Automatic ECU (e.g., P28-A51, P06-A52) to Manual:

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

RP resistor array before conversion Factory automatic resistor configuration showing RP17 and RP18 populated.

RP resistor array after manual conversion Converted manual configuration showing RP17 empty and RP18 jumpered with a wire.

JDM Automatic to Manual Conversion

JDM ECUs (typically large-case or small-case JDM P30, P72, or PR3) do not use the USDM RP17/RP18 configuration. Instead, they use a single resistor at RP18 located on the back side of the board near the corner.

  1. Locate resistor RP18 on the back side of the ECU board.
  2. De-solder the factory 2.4k Ohm resistor.
  3. Replace it with a 1.4k Ohm resistor.

USDM Manual to Automatic Conversion

If you need to run an automatic car on an originally manual ECU:

  1. Remove the jumper wire at RP18.
  2. Install a 2.7k Ohm resistor at RP18.
  3. Install a 4.7k Ohm resistor at RP17.
  4. Add the transmission solenoid driver chip/transistor array at position IC16 (typically a 5050S chip or equivalent) if it is missing from the manual board.

Related

Credits and source

Authors blundar, drdisco69

Source Adapted from OBD1 Civic Integra Auto Manual on pgmfi.org wiki. Licensed under CC BY-NC-SA 1.0.