Diagnostic Circuit Check
Diagnostic Circuit Check:
PURPOSE
The DIAGNOSTIC CIRCUIT CHECK ensures the self-diagnosis system works, determines trouble codes to be displayed and guide diagnosis to other problem areas.
"Check Engine" Light:
Diagnostic Connectors:
UNIT LOCATION AND IDENTIFICATION
- A white trouble code "Test" lead is located near the ECM.
- A black "Ground" lead is located near the ECM.
- The ECM is in the drivers kick panel.
- The CHECK ENGINE light is in the instrument cluster.
SYSTEM MONITOR OPERATION
With the engine running, if a problem in the system develops related to emission performance, the CHECK ENGINE lamp will come ON and a trouble code will be stored in the ECM "Trouble Memory". The lamp will remain "ON" with engine running as long as the problem exists. If intermittant, the CHECK ENGINE lamp will go out but the trouble code will be stored in the ECM memory.
LAMP CHECK OPERATION
With the key on and the engine OFF, the lamp should illuminate to indicate that the lamp works.
INSPECTION PROCEDURE Refer to the diagnostic chart.
- Turn the key ON and connect the "Test" and "Ground" leads.
- The CHECK ENGINE light will begin to flash code 12.
Reading Trouble Codes:
- 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.
- Faults indicated by codes 13, 31, 44 and 45 require engine operation at part throttle for up to five minutes after engine warm-up before the "Check Engine" light will come on and store a code. Code 15 takes five minutes of engine operation before it will display. Disconnect the test leads before starting the engine.
RESULTS OF INSPECTION
- A trouble code indicates a fault within the circuit or component (this includes the component, wiring, connectors or ECM).
- Proceed to the appropriate trouble code chart listed under DIAGNOSTIC CHARTS / TROUBLE CODES.
- When the engine is started, the CHECK ENGINE lamp will go out. If the light remains ON, the self-diagnosis system has detected an active fault.
- If the light has gone out, this indicates an intermittant problem.
NOTE:Faults indicated by codes 13, 31, 44 and 45 require engine operation at part throttle for up to five minutes after engine warm-up before the "Check Engine" light will come on and store a code. Code 15 takes five minutes of engine operation before it will display. Disconnect the test leads before starting the engine.
INTERMITTENT "CHECK ENGINE" LIGHT, NO STORED CODES
These conditions will cause an intermittent "Check Engine" light without storing trouble codes:
- If engine speed drops below 200 rpm for any reason, the light will come on until rpm exceeds 200 and for four seconds thereafter.
- Low battery voltage (under 9V) at ECM.
- Loss of trouble code memory. Momentarily grounding the dwell lead with engine at idle should store code 23. After engine is stopped and ignition turned "ON," check for voltage at ECM terminal "C46-1" and for code 23. If voltage is present but no code is stored, ECM is defective.
- Poor electrical connection at:
^ Ignition coil to ECM terminal "C46-10".
^ Battery to ECM terminal "C46-1".
^ ECM terminal "C46-13" to engine ground.
^ ECM terminal "C46-4" to lamp driver.
^ ECM terminal "C46-3" to Battery (including ECM relay circuit).