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On this page the OBD1 sheme’s known to me are presented EDM (Europen Domestic Market) style. The biggest difference between EDM and USDM (United States Domestic Market) is the ELD circuit (Electric Load Detection) that misses and the KS (Knock Sensor). Some connections are only found on P28 and P30 ECU’s. Those are marked coloured red. Some connections are different from car to car. Those are marked grey.


Nomenclature:

ACC - A/C relay

ACS - A/C switch

ALTC - Alternator relay, for control purposes, not present on all ECU’s

ALTF - Alternator switch

BKSW- Brake switch, for control purposes, not present on all ECU’s

CKP - Crankshaft position, (P)ulse or (M)ass, gives several pulses (~20?) during each cam shaft rotation

CYP - Cylinder position, (P)ulse or (M)ass, gives one pulse during each cam shaft rotation

DLC - Diagnostic connector, communication signal to the 3 wire connector next to the SCS connector

ECO - Unknown function (is there an ECO light on D15Z3?)

ECT - Engine coolant temperature

EGR - Exhaust gas recirculation

EGRL - Unknown function (probably related to EGR)

FANC - Fan relay, for control purposes, not present on all ECU’s

FLR - Fuel relay, 1 is always present, 2 can be ignored

IACV - Idle air control valve, controls the 2 wire type IACV valve

IAT - Intake air temperature

ICM - Ignition pulses, 1 is always present, 2 can be ignored

IGP - Battery feed, only active when key is turned

INJ - Injector, the number refers to the cylinder used (1 is on the side with the belts)

LG - Ground for battery circuit

MAP - Manifold absolute pressure

MIL - Motor indication light, this one gives the control engine light (CEL) signal

PCS - Control solenoid, this one is for the small black cylindric valve on the back of the IM

PG - Ground for battery circuit

PO2H - Primary oxygen sensor heater, connects with the ground of the car to activate the heater

PO2S - Primary oxygen sensor signal

SCS - Service connector switch, checks if the SCS connector is hot wired (for reading engine error codes)

SG - Ground for 5V circuit, 1 is for the MAP sensor, 2 is for the other sensors

STS - Starter switch

TDC - Top dead centre, (P)ulse or (M)ass, gives four pulses during each cam shaft rotation

TPS - Throttle position signal

VBU - Back up battery feed, always active (unless battery is removed)

VCC - 5V feed, 1 is for the MAP sensor, 2 is for the other sensors

VREF - Unknown function (probably related to wideband oxygen)

VSS - Vehicle speed sensor

VTM - Oil pressure switch, only -but not always- present on VTEC equiped vehicles

VTS - VTEC solenoid, only present on VTEC equiped vehicles

Below I also provided a D15Z3 sheme. Unfortunatly not each function of all pins are known to me. I do know that most question marks are connected to either the EGR (Exhaust Gas Recirculation) and wideband lambda sensor system (Yes this car has a wideband oxygen sensor system normally. However, I do not know the exact possibilities of this sensor). I used the sheme succesfully for a P28 ECU swap once. The wideband lambda wires can be re-used for a normal 4-wire lambda sensor. The VTM pin can be short circuited to the VTS pin to prevent VTEC error codes from the P28 ECU.

Here is the information you need to read error codes on 92-95 Civic and Del Sol (CRX). Those cars are OBD-I, so the same info should be usable for any other OBD-I Honda.

There is a 2-pin (most likely green in color) connector by the ECU or somewhere under the passenger's side dash. It's a Data Link Connector. Connect it's two pins with a piece of wire. Watch out not to get jolted while you're connecting the pins.

You will read error codes on the gauge cluster, on the Malfunction Indicator Lamp. Turn the key to position "II" and watch the lamp blink. Error codes are reported by a number of blinks.

There are short and long blinks. Long blinks mean 10, and short blinks mean 1. For example, if you get "long-long-short-short-short", it means error code 23. There is a short pause between each flash (long or short) and a long pause between 2 error codes. There will always be long flashes before short flashes. So you cannot expect number 23 to be reported as "short-long-short-long-short".

Take note of all error codes reported by ECM (Electronic Control Module). Find a list online that explains "OBD-I error codes honda" and you will find out what your problems are.

Do not forget to remove the wire from the 2-pin connector once you are done.

Honda ECU error codes

0 Bad ecu (if cel is on and no code or light stays on)

1 Oxygen Sensor "A" (Primary) defective circuit or unplugged / defective sensor

2 Oxygen Sensor "B" defective circuit or unplugged / defective sensor

3 MAP Sensor (Manifold Absolute Pressure) defective circuit or unplugged / defective sensor

4 CKP Sensor (Crankshaft Position Sensor) defective circuit or unplugged / defective sensor

5 MAP Sensor (Manifold Absolute Pressure) mechanical problem / disconnected piping

6 ECT Sensor (Engine Coolant Temperature) defective circuit or unplugged / defective sensor

7 TP Sensor (Throttle Position) defective circuit or unplugged / defective sensor

8 TDC Sensor (Top Dead Center) defective circuit or unplugged / defective sensor

9 CYP Sensor (Cylinder) defective circuit or unplugged / defective sensor

10 IAT Sensor (Intake Air Temperature) defective circuit or unplugged / defective sensor

12 EGR Lift Sensor (Exhaust Gas Recirculation) defective circuit or unplugged / defective sensor

13 BARO Sensor (Atmospheric Pressure) defective circuit or unplugged / defective sensor

14 IAC Valve (Idle Air Control) defective circuit or unplugged / defective sensor

15 Ignition Output Signal missing or defective ignition output signal

16 Fuel Injector System defective circuit or unplugged / defective fuel injector

17 VSS (Vehicle Speed Sensor) defective circuit or unplugged / defective sensor

19 Automatic Transmission Lock Up Control Solenoid Valve defective circuit or unplugged / defective solenoid valve

20 Electrical Load Detector defective circuit or unplugged / defective sensor

21 VTEC Solenoid Valve defective circuit or unplugged / defective solenoid valve

22 VTEC Oil Pressure Switch defective circuit or unplugged / defective oil pressure switch

23 KS (Knock Sensor) defective circuit or unplugged / defective sensor

30 Automatic Transmission Signal: "A" / SEAF / SEFA / TMA or TMB defective circuit or unplugged / defective sensor

31 Automatic Transmission Signal "B" defective circuit or unplugged / defective sensor

41 Primary Oxygen Sensor - Heater circuit malfunction


43 Fuel Supply System defective or malfunctioning fuel supply system

45 System Too Lean or Too Rich malfunction in the fuel monitoring systems

48 LAF Sensor (Lean Air Fuel) defective circuit or unplugged / defective sensor

54 CKF Sensor (Crankshaft Speed Fluctuation) defective circuit or unplugged / defective sensor

58 TDC Sensor 2 (Top Dead Center) defective circuit or unplugged / defective sensor

61 Oxygen Sensor, Heated - Sensor 1 (Primary) high voltage, low voltage, or slow response

63 Oxygen Sensor, Heated - Sensor 2 (Secondary) high voltage, low voltage, or slow response

65 Oxygen Sensor Heater (Secondary) malfunctioning or defective oxygen sensor heater

67 Catalyst system Efficiency Below Threshold malfunctioning or defective catalyst system

70 Automatic Transmission malfunction with the automatic transmission controls

71 Cylinder 1 Misfire or a Random Misfire a condition is present that is creating a cylinder misfire

72 Cylinder 2 Misfire or a Random Misfire a condition is present that is creating a cylinder misfire

73 Cylinder 3 Misfire or a Random Misfire a condition is present that is creating a cylinder misfire

74 Cylinder 4 Misfire or a Random Misfire a condition is present that is creating a cylinder misfire

75 Cylinder 5 Misfire or a Random Misfire a condition is present that is creating a cylinder misfire

76 Cylinder 6 Misfire or a Random Misfire a condition is present that is creating a cylinder misfire

80 Exhaust Gas Recirculation insufficient flow detected

86 ECT Sensor (Engine Coolant Temperature) circuit range / performance problem

90 Evaporative Emission Control System leak detected in the fuel tank area

91 Fuel Tank Pressure Sensor low input

92 Evaporative Emission Control System insufficient purge flow