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Isuzu Trooper Check Engine Light Trouble Code Reading

How to check what trouble code a check engine light means on a first generation Isuzu Trooper (1981–1991).

Step-by-step instructions

If a problem develops in a monitored system with the engine running, the ***Check Engine*** light (CEL) will come ***ON*** and a trouble code will be stored in ECM memory.
As long as a problem is present, the light will remain on while the engine is running. If the problem is intermittent, the light will go out but a trouble code will be stored in ECM memory.
As a bulb check, the Check Engine light will come on with the ignition switched on and the engine not running. If no codes are present, the light will go out upon starting the engine. If the light remains on, the system has detected a fault.

To access trouble codes, a test lead (white wire) and ground lead (black wire) are branched from the wiring harness under the center console near the ECM.
With the ignition "ON" connect these two leads together.
The "Check Engine" light will begin to flash code 12. Code 12 consists of one flash, a short pause, then two flashes. After a longer pause, code 12 will repeat two more times.
This check indicates that the on-board diagnostic system is functioning. If no other codes are present, the cycle will repeat until the ignition is switched "OFF."

If trouble codes are stored in memory, the lowest number code will flash three times followed by the next higher code number until all stored codes have been displayed.
The codes will then repeat in the same order until the test lead is disconnected. Code 14, for example, indicates a problem in the coolant sensor circuit.
To clear a code from memory, disconnect the battery.

CODE 12: Indicates that on-board diagnostics are functioning when diagnostic leads are connected and ignition is "ON" (engine not running). Code not stored in memory.
CODE 13: Oxygen sensor defective or open circuit.
CODE 14: Shorted coolant sensor circuit.
CODE 15: Open coolant sensor circuit.
CODE 21: Both idle and wide open throttle ON simultaneously in throttle valve switch.
CODE 22: Open or shorted starter signal circuit.
CODE 23: Shorted power transistor output terminal.
CODE 25: Open or shorted circuit for pressure regulator VSV.

CODE 26: Open or shorted circuit for canister VSV.
CODE 27: Open in ECM driver transistor for canister VSV.
CODE 32: EGR gas temperature sensor malfunction.
CODE 33: Open or shorted circuit in fuel injector harness, dropping resistor or inside ECM.
CODE 34: EGR gas temperature sensor or wiring faulty.
CODE 35: Ignition power transistor harness open circuit.
CODE 41: Crank angle sensor open circuit or faulty signal.
CODE 43: Throttle valve switch idle contact continuously ON.

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