Warning Light Check

To test warning light and be sure the diagnostic system is operating, turn off the ignition switch, leave engine stopped and ground trouble code test lead located beneath dash (black/white wire with green connector, attached to ECM harness).

If the system is operating properly, the "CHECK ENGINE" light will flash a code "12", which indicates proper operation. The "12" will be flashed as follows: one flash, followed by a pause, and then two more flashes. After a longer pause, the code will repeat two more times.

NOTE: If fault is intermittent, "CHECK ENGINE" light may come on and then go out; however, fault problem will be stored in ECM memory so diagnosis can be performed.

C-4 SYSTEM DIAGNOSTIC TROUBLE CODES

Trouble Code	Explanation
12	No tach or reference signal to ECM.
13	Oxygen sensor circuit.
13 & 14	At same time, refer to code 43
14	Shorted coolant sensor circuit.
15	Open coolant sensor circuit.
21	Shorted wide open throttle circuit (if used). Throttle position sensor circuit.
22	Grounded closed throttle or wide open throttle switch circuit.
21 & 22	At same time, grounded wide open throttle circuit switch.
23	Open or grounded carburetor solenoid circuit.
32	Barometric pressure sensor output low.
32 & 55	At same time, grounded +8V, V (REF) or faulty ECM.
34	Manifold absolute pressure sensor output high.
43	Throttle position sensor adjustment.
44	Lean oxygen sensor.
45	Rich oxygen sensor.
44 & 45	At same time, faulty oxygen sensor or open sensor.
51	Faulty calibration (PROM) unit or improper PROM installation.
52 & 53	"CHECK ENGINE" light off - intermittent ECM problem, "CHECK ENGINE" light on - faulty ECM.
54	Faulty carburetor solenoid and/or ECM.
55	Faulty oxygen sensor, open manifold absolute pressure sensor or ECM (3.8L V6), faulty ECM or throttle position sensor (exc. 3.8L V6).