Test Procedures

When diagnosing and testing system refer to SCHEMATIC DIAGRAMS/ELECTRICAL AND ELECTRONIC DIAGRAMS for wiring diagrams.

Fig. 2 ECM Connector Pin Locations:

1. With ignition off, disconnect ECM connectors C1 and C2, Fig. 2, then turn ignition switch to Run position, place cruise control in Off position and measure voltage between terminal C2/20 (gray wire, except Beretta and Corsica) or C1/20 (gray wire, Beretta and Corsica) and ground.
2. If battery voltage is available, replace multi-function lever.
3. If no voltage is available, place cruise switch in On position and measure voltage between terminal C2/20 (gray wire, except Beretta and Corsica) or C1/20 (gray wire, Beretta and Corsica) and ground.
4. If no voltage is available on models except Beretta and Corsica, check Radio (Century, Ciera/Cutlass Cruiser, Skyhawk) Rad (Cavalier and Sunbird) ECM 4 Cyl (Skylark) ECM Relays (Grand Am) fuse or fuse No. 18 (Calais) check cruise switch, brown/white wire (circuit 141, Cavalier, Century, Ciera/Cutlass Cruiser, and Skyhawk) or pink/black wire, (circuit 430, Skylark; circuit 439, Calais and Grand Am) and gray wire (circuit 397, except 1989 Ciera/Cutlass Cruiser) or yellow wire (circuit 43, 1989 Ciera/Cutlass Cruiser) for an open. If no voltage is available on Beretta and Corsica, check brown/white wire (circuit 141) and gray wire (circuit 397) multi-function lever and cruise control switches for an open.
5. If battery voltage is available, measure voltage between terminal C1/14 (brown wire) and ground.
6. If no voltage is available, on Beretta, Calais, Cavalier, Century, Ciera/Cutlass Cruiser, Corsica, Grand Am or Skyhawk, check brake switch, cruise control clutch switch (except Ciera/Cutlass Cruiser) gray wire (circuit 986, except Beretta and Corsica) or tan wire (circuit 986, 1989 Beretta and Corsica) or dark green wire (circuit 986, 1990 Beretta and Corsica) and brown wires (circuits 86 and 986, Cavalier, Skyhawk and Sunbird) brown and brown/white wires (circuit 86, Calais and Grand Am) or brown wires (circuit 86, Beretta, Century, Ciera/Cutlass Cruiser and Corsica) for an open. If no voltage is available on Skylark, check cruise switch and gray/white and gray/red wires (circuit 87) for an open.
7. If battery voltage is available, depress brake pedal while measuring voltage between terminal C1/14 (brown wire) and ground.
8. If battery voltage is available, adjust or replace cruise brake switch as necessary.
9. If there is no voltage available, measure voltage between terminal C2/21 (dark blue wire) and ground. If battery voltage is available, check set switch for a short.
10. If no voltage is available, press set button while measuring voltage between terminal C2/21 (dark blue wire) and ground.
11. If no voltage is available, check set switch and dark blue wire (circuit 84) for an open.
12. If there is battery voltage, measure voltage between terminal C2/4 (gray/red wire, Skylark, Grand Am, Skyhawk and 1989 Century and Sunbird and 1989 Calais; gray/black wire, Beretta, Cavalier, Ciera/Cutlass Cruiser, Corsica and 1990 Calais, Century, and Sunbird) and ground.
13. If battery voltage is available, check cruise switch for short.
14. If no voltage is available, hold cruise switch in Resume/Accel position while measuring voltage between terminal C2/4 (gray/red wire, Grand Am, Skyhawk and Skylark 1989 Century and Sunbird and 1989 Calais; gray/black wire, Beretta, Cavalier, Ciera/Cutlass Cruiser, Corsica and 1990 Calais, Century and Sunbird) and ground.
15. If no voltage is available, check cruise switch and gray/red and gray/white wires (circuit 87, Grand Am, Skyhawk and Skylark and 1989 Calais) gray/white and gray/black wires (circuit 87, 1990 Calais) gray/black wires (circuit 87, Beretta, Cavalier, Century, Ciera/Cutlass Cruiser, Corsica and Sunbird) for an open.
16. If battery voltage is available on vehicles with automatic transaxle, place shift lever in D position and measure continuity between terminal C2/18 (orange/black wire) and ground.
17. If reading is infinite ohms, check transaxle position switch and orange/black wire (circuit 434) for a short to ground.
18. If reading is 0 ohms, or there was battery voltage available in step 14 on vehicle with manual transaxle, measure resistance between terminal C1/10 (light green wire) and ground. Disconnect negative battery cable before measuring resistance on Ciera/Cutlass Cruiser, Century, Skylark, Sunbird and 1989-90 Grand Am.
19. If resistance is less than 30 ohms, check for short to ground in light green wire (circuit 402) or in cruise control servo.
20. If resistance is greater than 55 ohms, check for open in cruise control servo, light green wire (circuit 402) or black wire (circuit 150).
21. If resistance is 30-55 ohms, measure resistance between terminal C1/11 (dark blue/white wire, except Beretta and Corsica), (dark blue wire, Beretta and Corsica) and ground.
22. If resistance is less than 30 ohms, check for short to ground in dark blue/white and, on Beretta and Corsica in cruise control servo.
23. If resistance is greater than 55 ohms, check for open in cruise control servo or dark blue/white wire and, on Beretta and Corsica, dark blue wire (circuit 403).
24. If resistance is 30-55 ohms, proceed as follows:
a. Reconnect ECM and, on Century, Ciera/Cutlass Cruiser, Skylark, Sunbird and 1989-90 Grand Am, the negative battery cable.
b. Remove connector from cruise control servo.
c. Jumper terminal C of cruise control servo to ground.
d. Jumper terminal A of cruise control servo to battery.
e. Run engine for 1 minute, then turn engine off.
f. Jumper terminal E of servo to battery.
25. If vacuum does not pull servo in, proceed as follows:
a. Check for blocked or leaking vacuum source, repairing as necessary.
b. If vacuum source is satisfactory, remove jumper from terminal E of servo and proceed to step 27.
26. If vacuum pulls servo all the way in, proceed as follows:
a. Remove jumper from terminal E of servo.
b. If vacuum holds servo all the way in, replace ECM.
c. If vacuum does not hold servo all the way in, proceed to step 27.
27. Plug vacuum release port, run engine for 1 minute, turn engine off and jumper terminal E of servo to battery.
28. If vacuum does not pull servo in, replace cruise control servo.
29. If vacuum pulls servo all the way in, remove jumper from terminal E of servo.
30. If vacuum does not hold servo all the way in, replace cruise control servo.
31. If vacuum holds servo all the way in, repair or replace cruise control vacuum release valve or the hose to it.