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31,217 Posts

not for the P74/P75 ECU which is what you should be searching under. It's not limited to are looking for an OBD1 P74/P75 pinout

I only have 1 for the OBD1 P72 GSR pin out

This is from but is generalised to all Honda OBD1 ECU's:


A1-INJ1 INJ1 Brown, Battery Voltage with KOEO
A2-INJ4 INJ4 Yellow, Battery Voltage with KOEO
A3-INJ2 INJ2 Red, Battery Voltage with KOEO
A4-VTS VTEC solenoid GRN/YEL, N/a
A5-INJ3 INJ3 Blue, Battery Voltage with KOEO
A6-PO2SHTC O2 sensor (heating element) Org/Wht, Battery Voltage with KOEO
A7-FLR1 fuel pump Grn/BLK, Battery Voltage with KOEO
A8-empty A7 and A8 have the same circurt, so they can be the same
A9-IACV IAC valve Blk/Blu, About 10v KOEO on Warm engine
A11- This is EGR Control Solenoid Valve (if the ECU has) Red, N/A
A12-FANC engine coolant temp switch Blu/red, N/A
A13-MIL MIL (check engine light) Blu/wht, N/A
A15-ACC (a/c compressor clutch) Red/Blu, N/A
A16-ALT C alternator Wht/Grn, N/A
A17-IAB IAB Solenoid Pink, N/A
A18- Org/Red, Transmission Control Module (A/T), N/A
A19- White, Intake control solenoid, Battery Voltage with KOEO
A20-PCS EVAP purge control solenoid Red/Grn, N/a
A21-ICM ICM Yel/Grn, Ignition Control Module (ICM) Output signal, About 10V KOEO
A22- *per Sander* Ignitor same as A21
A23-PG1 ground Black, Power ground, less than 1V
A24-PG2 ground same as A23
A25-IGP2 to main relay and to gound for o Yel/blk, Battery positive from Main relay, Battery Voltage with KOEO
A26-LG1 gound Blk/red, less than 1V

B1-IGP2 to pin A25 Yel/Blk, Battery positive from Main relay, Battery Voltage with KOEO
B2-LG2 ground to shields for CYP & TDC Brown/Blk, Less than 1V
B3- Orange, upshift/downshift comparative input, N/A
B4- Pink, upshift/downshift comparative input, N/A
B5-ACS a/c switch Blu/Blk, A/c input, About 5V with KOEO & A/C off; less than 1V KOER with A/C & blower on
B7- Light green, Park/Neutral switch (A/T), Less than 1V in Park or Neutral with KOEO; 5V in Park or neutral with KOER; Battery voltage in all other positions
B8-PSPSW PSP switch Red/Green, Power steering oil pressure switch, 0V KOEO; Battery Voltage KOER While slowly turning steering wheel
B9-STARTER SIGNAL starter signal Blue/red, Battery Voltage in the START position (clutch depressed on M/T models)
B10-VSS vehicle speed sensor Orange, Pulses 0-12V while turning the left front wheel
B11-CYP P CYP -P Orange, CYP sensor input, N/A
B12-CYP M CYP -M White, CYP sensor signal, N/A
B13-TDC P TDC -P Org/Blue, TDC sensor input, N/A
B14-TDC M TDC -M Wht/Blue, TDC sensor signal, N/A
B15-CKP P CKP -P Blu/Green, CKP Sensor input, N/A
B16-CKP M CKP -M Blu/yel, CKP Sensor signal, N/A

D1-VBU Back Up Power Wht/Yel, Battery positive From battery through Fuse Box, Battery Voltage at ALL times
D2-BKSW brake switch Grn/wht, Battery voltage at all times
D3-KS Knock Sensor Red/Blue, N/A
D4-SCS service check connector Brown/Wht, About 5V (M/T); About 11V (A/T)
D6-VTM VTEC pressure switch Light Blue, N/A
D7-TXD/RXD (data link connector) Light Green/Red, N/A
D9-ALT F alternator Wht/Red, Alternator Charging Signal, About 4.5V KOEO; Decreases under Electrical load (Headlights & rear defogger on) At warm idle
D10-ELD electric load detector input Grn/Blk, N/A
D11-TPS TPS Signal Red/Blk, About 0.5V KOEO with throttle fully closed; About 4.5V KOEO with throttle fully open
D12- Wht/Blk, EGR Valve Lift sensor, About 1.2V KOEO
D13-ECT ECT sensor input Yel/Blu, About 5V KOEO (varies with temperature)
D14-PHO2S O2 sensor White, heated 02 sensor Signal, 0.4-0.5V when ignition is turned on; drops to less than 0.1V within 2 minutes
D15-IAT IAT sensor Red/Yel, Intake Air Temperature signal, .05-4.5V KOEO(Varies with temperature)
D16-VREF VREF shows BLANK on my diagram
D17-MAP Map Signal Wht/Blu, About 3V KOEO (Varies with Temperature)
D18- Light Green/Blk, Transmission Control Module (A/T only), N/A
D19 - Red/Wht, Reference Voltage, About 5V KOEO
D20 - Yel/Wht, Reference Voltage, About 5V KOEO
D21 - Blue/Wht, Sensor ground, Less than 1V
D22 - Green/Wht, Sensor ground, Less than 1V

there is no "C' section


728 Posts
Yeah, i know I did not limit it to 94.

Do you hapen to know what the differences are in the vtec ecu vs non? Are the majority of the wires the same? The main difference being the addition of vtec?

I am truly suprised there is not a few schematics of the obdI ls ecu harness kicking about.

728 Posts
Oh, i missed the "This is from but is generalised to all Honda OBD1 ECU's:"

And assumed you were posting more vtec. Thank you sir!

How close to the p75 is this?

Rather are all the marked pins correct?

31,217 Posts
this is the best or closest I can get for you but the better bet is to get the actual pinout from a Helms Manual for your model.

have you looked at Apex's SAFC wiring diagrams for your model...that may be another source on their website's documentation pdf files but those aren't detailed either anyway.

another person to contact who is good with this info (but I don't know if he'll release it for free) is katman on honda tech or you could try kenji at honda tech who also is the resident ecu pinout wizard.

I suggest you go with the Helms.

728 Posts
I could not find it in the helms :( I have searched the internet for a few days now and am begining to think there is no posts anywhere reguarding the p75.

No one has a pic of the page in the helms that has the ecu pinout for p75?
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