How to Retrieve OBD1 CEL Codes by Jumping the Service Connector

CEL = Check Engine Light in gauge cluster
D4 = Automatic transmission D4 light in gauge cluster
SRS = Supplemental Restraint System (Airbags) light in gauge cluster

ABS = Anti-Lock Brake System light in gauge cluster
OBD = OnBoard Diagnostics system (92-95 OBD1; 96-00 OBD2)
ECU = Electronic Control Unit (car's computer)


1) On the passenger side, remove the kick panel at the floor. Behind it is your ECU and a jumper plug (aka the Service Connector).


2) Locate the jumper plug. It's a 2-pin/wire plug.




3) With the key OFF, insert either a 2-pin connector clip or a loop of wire (e.g., a paper clip) into both holes on the connector. (Checkout these cool Race Spec CEL Jumpers

4) Back in the driver's seat, turn the key to the ON position but do NOT start the car. The CEL will come on like normal but will then begin to flash.

**By counting the number of flashes, you can decipher the CEL code**
A LONG flash (1 second) is 10
A SHORT flash (0.5 second) is 1

For example, two long flashes followed quickly by two short flashes would be code 22. If there is more than one code, each code will be separated by a 2.5 second gap.


5) Now that you have pulled the CEL codes, clear them by resetting the ECU


1 O2A - Oxygen sensor #1
2 O2B - Oxygen sensor #2
3 MAP - manifold absolute pressure sensor
4 CKP - crank position sensor
5 MAP - manifold absolute pressure sensor
6 ECT - water temperature sensor
7 TPS - throttle position sensor
8 TDC - top dead center sensor
9 CYP - cylinder sensor
10 IAT - intake air temperature sensor
12 EGR - exhaust gas recirculation lift valve
13 BARO - atmospheric pressure sensor
14 IAC (EACV) - idle air control valve
15 Ignition output signal
16 Fuel injectors
17 VSS - speed sensor
19 Automatic transmission lockup control valve
20 Electrical load detector
21 VTEC spool solenoid valve
22 VTEC pressure valve
23 Knock sensor
30 Automatic transmission A signal
31 Automatic transmission B signal
36 traction control found on JDM ECU's
38 Secondary VTEC solenoid on JDM 3 stage D15B VTEC ECUs (P2J)
41 Primary oxygen sensor heater
43 Fuel supply system
45 Fuel system too rich or lean
48 LAF - lean air fuel sensor
54 CKF - crank fluctuation sensor
58 TDC sensor #2
61 Primary oxygen sensor
63 Secondary oxygen sensor circuit
65 Secondary oxygen sensor heater wire (black wires)
67 Cat Converter
70 Automatic transmission problem
71 random misfire cylinder 1
72 random misfire cylinder 2
73 random misfire cylinder 3
74 random misfire cylinder 4
80 EGR Valve/Line
86 ECT sensor - Cooling System
90 Evaporative Emission Control System Leak
91 Fuel Tank pressure sensor
92 EVAP Solenoid/Valve/Vacuum Lines

    6) Now that you know what OBD1 CEL codes are thrown, you can begin to go about fixing it


Tip #1: Does my CEL work?

To know whether your CEL works, turn the key from off to the ON(II) position. The CEL should turn on and then off after 2 seconds. If the CEL never turns on, this could mean that the CEL bulb in the cluster is blown, a CEL wire is bad, or a previous owner has removed the CEL bulb to mask a problem that would have hindered sale of the car.

Tip #2: How do I verify that no CEL codes are thrown?
If the CEL works but does not remain on steady with the key in ON(II) or while driving, then no CEL codes are thrown. In this case, if you jump the service connector, the CEL will remain on steady rather than blink some codes.

Tip #3: My CEL turns on while driving but I can't pull any codes?

In some cases, the CEL of 5th generation Civics (92-95) may turn on while driving, but if the engine is turned off, the CEL and CEL code will be lost. The workaround to allow recovery of the code when this happens is to safely pull to the side of the road and leave the engine running while you jump the service connector.

Tip #4: How do I reset the ECU to clear the CEL codes?
After you retrieve the CEL codes, then reset the ECU to clear the codes. This is done by removing the 7.5A hood Back Up fuse for 3 minutes or more and then reinserting it. Then drive the car to see whether the CEL again remains on steady. If so, pull the codes again to see whether any of the original codes has repeated. This step is important because you only want to troubleshoot codes that repeat. In general, ignore codes that pop up once but don't repeat.

Honda Tech - Original Source