Third generation preludes came with a variety of ECUs. The most common one, called the PK2, is described below.


PK2 is the code assigned to a set of Honda ECUs used in 3rd generation Preludes. The PK2 belongs to a family of OBD0 ECUs used in Honda cars equiped with MPFI during the late eighties and early nineties.

The PK2's circuit board is very similar to some other OBD0 ECUs, specifically the PG7, PM6, PM7, PP5, PR5, PS9 and XE5. A list on indicates that these other ECUs can be found in the following cars:

PG7 - 88-89 Integra (D16A1 engine equiped with Electronic Advance) PM6 - 88-91 Civic/CRX SOHC Si (1.6L SOHC) PM7 - 89-91 Civic Si DOHC ZC PP5 - 88-94 Concerto PR5 - 90-91 JDM Integra ZXi (1.6L SOHC) PS9 - 90-91 USDM Civic EX (1.6L SOHC - usually auto) XE5 - 88-91 Mugen Race ECU for ZC series motors?

The PK2's Microcontroller

The PK2 uses an OKI 8XC154 processor to run the code programmed to the ECUs ROM. 8XC154 processors understand Intel's 8051 assembly language. The OKI 8xC154 microcontrollers are slightly odd because they have one propriety command, A5, that other Intel 8051 compatible microcontrollers will not understand. The result is that you won't be able to run the stock program in any other microcontroller other than an OKI 8xC154. Annoying.

There seem to be two variants of OKI 8XC154 chips found in Honda ECUs, the 83C154 and the 80C154.

The OKI 83C154 is a 40-pin microcontroller with a built in ROM. OKI 83C154 chips seem to have been used by Honda during 1988 and 1989. Because the ROM is internal to the microcontroller, in order to re-program an ECU eqipped with an 83C154 the entire microcontroller must be replaced. During the author's research on this topic no indication was found that this has ever been done sucessfully, although, some people claim that the 83C154 can be replaced with an Atmel AT89C55 chip.

The similar OKI 80C154 has no built in ROM but rather makes use of an external 28-pin EPROM chip. It seems that Honda used the 80C154 chip during 1990 and 1991. Because it features an external EPROM chip, PK2 ECUs with an 80C154 microcontroller are a lot easier to re-program than the earlier 83C154. All that must be done is that the EPROM chip must be reprogrammed.

USDM PK2 Pinout

Connector A

Pin / Unit / Wire Color

A1 Injector #1 Brown

A2 Ground Black

A3 Injector #2 Red

A4 Ground Black

A5 Injector #3 Blue

A6 N/A N/A

A7 Injector #4 Yellow

A8 Bypass Control Sol Yellow

A9 N/A N/A

A10 EGR Control Sol Red

A11 EACV Control Blue-Red

A12 Fuel Pump Relay Green-Black

A13 Main Relay Input Yellow-Black

A14 Fuel Pump Relay Green-Black

A15 Main Relay Input Yellow-Black

A16 Ground Brown-Black

A17 Power Input White-Yellow

A18 Ground Black-Red

Connector B

Pin / Unit / Wire Color

B1 A/C Compressor Control Rly Red-Blue

B2 Purge Cutoff Solenoid Yellow-Black

B3 N/A N/A

B4 N/A N/A

B5 Ignition Timing Input Brown

B6 PGMFI Ind Light Yellow-Red

B7 Park/Neut Input Green

B8 A/C Red-Green

B9 N/A N/A

B10 Crank Sensor Input Blue-Green

B11 Oxygen Sensor "B" Red-Blue

B12 Crank Sensor Input Blue-Yellow

B13 Starter Input Blue-Red

B14 ALT RF Input White-Red

B15 Igniter Control White

B16 Speed Sensor White-Blue

B17 Igniter Control White

B18 P/S Press SW Input Blue-Red

B19 A/T Control Unit Yellow-White

B20 N/A N/A

Connector C

Pin / Unit / Wire Color

C1 Cyl Sensor Input Orange

C2 Cyl Sensor Input White

C3 TDC Sensor Input Orange-Blue

C4 TDC Sensor Input White-Blue

C5 Intake Air Temp Sens White-Red

C6 Coolant Temp Sens Yellow-Green

C7 TPS Input Red-Yellow

C8 EGR Sensor Input Yellow

C9 Atmosphere Press Sens Red

C10 N/A N/A

C11 MAP Sensor White-Blue

C12 Sensor Ground 2 Green-White

C13 VCC2 Yellow-White

C14 Sensor Ground 1 Blue-White

C15 VCC1 Red-White

C16 Oxygen Sensor "A" White


PK3 is the identifier assigned to a type of OBD1 Honda ECU found in 1990-1991 Honda Preludes powered by a B21A1 engine.