Frequently Asked Question

Honda OBD1 ECU Pinout & Pin Designations
Last Updated a year ago

These are the pin designations for the OBD1 ECU as well as their wire color and voltage. I always have a hard time finding this information when I need it as I'm sure others do, so here it is

KEY:
(voltage values measured in DC Volts unless otherwise specified)
V = Volts
Wht = White
Blk = Black
Grn = Green
Yel = Yellow
Brn = Brown
Blu = Blue
Org = Orange

A, B, D= Slot. Numbers are read up and down from left to right, not straight across

A1-INJ1 INJECTOR#1 Brown, Battery Voltage with KEY ON ENGINE OFF
A2-INJ4 INJECTOR#4 Yellow, Battery Voltage with KEY ON ENGINE OFF
A3-INJ2 INJECTOR#2 Red, Battery Voltage with KEY ON ENGINE OFF
A4-VTS VTEC solenoid GRN/YEL, n/a
A5-INJ3 INJECTOR#3 Blue, Battery Voltage with KEY ON ENGINE OFF
A6-PO2SHTC O2 sensor heating element Org/Wht, Battery Voltage KEY ON ENGINE OFF
A7-FLR1 fuel pump Grn/BLK, Battery Voltage KEY ON ENGINE OFF
A8-empty A7 and A8 have the same circurt, so they can be the same
A9-IACV IAC valve Blk/Blu, About 10v KEY ON ENGINE OFF on Warm engine
A10-empty
A11-EGR Control Solenoid Valve (if the ECU has it) Red, n/a
A12-FANC engine Error! Hyperlink reference not valid. temp switch Blu/red, n/a
A13-MIL MIL (check engine light) Blu/wht, n/a
A14-empty
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 KEY ON ENGINE OFF
A20-PCS EVAP purge control solenoid Red/Grn, n/a
A21-ICM Yel/Grn, Ignition Control Module output signal, About 10V KEY ON ENGINE OFF
A22-Igniter, 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 ground Yel/blk, Battery positive from Main relay, Battery Voltage with KEY ON ENGINE OFF
A26-LG1 gound Blk/red, less than 1V
B1-IGP2 to pin A25 Yel/Blk, Battery positive from Main relay, Battery Voltage with KEY ON ENGINE OFF
B2-LG2 ground to shields for CYP & TDC Brown/Blk, 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, ~5V with KEY ON ENGINE OFF & A/C off; B6-empty
B7-Light green, Park/Neutral switch (A/T), B8-PSPSW PSP switch Red/Green, Power steering oil pressure switch, 0V with KEY ON ENGINE OFF; Battery Voltage with KEY ON ENGINE RUNNING 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(#1 piston position) -P Orange, CYP sensor input, n/a
B12-CYP M CYP -M White, CYP sensor signal, n/a
B13-TDC P TDC(top dead ceter) -P Org/Blue, TDC sensor input, n/a
B14-TDC M TDC -M Wht/Blue, TDC sensor signal, n/a
B15-CKP P CKP(crank position) -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, ~5V (M/T); ~11V (A/T)
D5-empty
D6-VTM VTEC pressure switch Light Blue, n/a
D7-TXD/RXD (data link connector) Light Green/Red, n/a
D8-empty
D9-ALT F alternator Wht/Red, Alternator Charging Signal, ~4.5V with KEY ON ENGINE OFF; Decreases under Electrical load (Headlights & rear defogger on) At warm idle
D10-ELD electric load detector input Grn/Blk, n/a
D11-TPS (throttle position sensor) Signal Red/Blk, ~0.5V with KEY ON ENGINE OFF with throttle fully closed; ~4.5V with KEY ON ENGINE OFF with throttle fully open
D12-Wht/Blk, EGR Valve Lift sensor, ~1.2V with KEY ON ENGINE OFF
D13-ECT (engine coolant temp) sensor input Yel/Blu, ~5V with KEY ON ENGINE OFF (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 Intake Air Temperature sensor signal Red/Yel, .05-4.5V with KEY ON ENGINE OFF (Varies with temperature)
D16-VREF (no info)
D17-MAP Map Signal Wht/Blu, ~3V with KEY ON ENGINE OFF (Varies with Temperature)
D18-Light Green/Blk, Transmission Control Module (A/T Only), n/a
D19-Red/Wht, Reference Voltage, ~5V with KEY ON ENGINE OFF
D20-Yel/Wht, Reference Voltage, ~5V with KEY ON ENGINE OFF
D21-Blue/Wht, Sensor ground, D22-Green/Wht, Sensor ground,

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image source: https://technet.ff-squad.com/wiring.obd1.htm

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