Chevrolet Citation/Omega/Phoenix/Skylark 1980-1985 Repair Guide



The following explains how to activate the Trouble Code signal light in the instrument cluster. This is not a full-fledged C-4 or CCC System troubleshooting and isolation procedure.

Before suspecting the C-4 or CCC System or any of its components as faulty, check the ignition system including distributor, timing, spark plugs, and wires. Check the engine compression, air cleaner, and emission control components not controlled by the ECM. Also check the intake manifold, vacuum hoses and hose connectors for leaks and the carburetor bolts for tightness.

The following symptoms could indicate a possible problem with the C-4 or CCC System.

  1. Detonation
  3. Stalls or rough idle-cold
  5. Stalls or rough idle-hot
  7. Missing
  9. Hesitation
  11. Surges
  13. Poor gasoline mileage
  15. Sluggish or spongy performance
  17. Hard starting-cold
  19. Hard starting-hot
  21. Objectionable exhaust odors
  23. Cuts out
  25. Improper idle speed (CCC System only)

As a bulb and system check, the "Check Engine" light will come on when the ignition switch is turned to the ON position but the engine is not started.

The "Check Engine" light will also produce the trouble code or codes by a series of flashes which translate as follows. When the diagnostic test lead (C-4) or terminal (CCC) under the dash is grounded, with the ignition in the ON position and the engine not running, the "Check Engine" light will flash once, pause, then flash twice in rapid succession. This is a code 12, which indicates that the diagnostic system is working. After a longer pause, the code 12 will repeat itself two more times. The cycle will then repeat itself until the engine is started or the ignition is turned off.

When the engine is started, the "Check Engine" light will remain on for a few seconds, then turn off. If the "Check Engine" light remains on, the self-diagnostic system has detected a problem. If the test lead (C-4) or test terminal (CCC) is then grounded, the trouble code will flash three times. If more than one problem is found, each trouble code will flash three times. Trouble codes will flash in numerical order (lowest code number to highest). The trouble codes series will repeat as long as the test lead or terminal is grounded.

A trouble code indicates a problem with a given circuit. For example, trouble code 14 indicates a problem in the cooling sensor circuit. This includes the coolant sensor, its electrical harness, and the Electronic Control Module (ECM).

Since the self-diagnostic system cannot diagnose every possible fault in the system, the absence of a trouble code does not mean the system is trouble-free. To determine problems with the system which do not activate a trouble code, a system performance check must be made. This job should be left to a qualified technician.

In the case of an intermittent fault in the system, the "Check Engine" light will go out when the fault goes away, but the trouble code will remain in the memory of the ECM. Therefore, if a trouble code can be obtained even though the "Check Engine" light is not on, the trouble code must be evaluated. It must be determined if the fault is intermittent or if the engine must be at certain operating conditions (under load, etc.) before the "Check Engine" light will come on. Some trouble codes will not be recorded in the ECM until the engine has been operated at part throttle for about 5 to 18 minutes.

On the C-4 System, the ECM erases all trouble codes everytime the ignition is turned off. In the case of intermittent faults, a long term memory is desirable. This can be produced by connecting the orange connector/load from terminal "S" of the ECM directly to the battery (or to a "hot" fuse panel terminal). This terminal must be disconnected after diagnosis is complete or it will drain the battery.

On the CCC System, a trouble code will be stored until terminal "R" of the ECM had been disconnected from the battery for 10 seconds.


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Fig. Fig. 1 Test lead locations for 1980 vehicles with the C-4 system

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Fig. Fig. 2 Location of the test terminals for 1981-85 vehicles with the CCC system

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Fig. Fig. 3 no caption

On the C-4 System, activate the trouble code by grounding the trouble code test lead. Use the illustrations to locate the test lead under the instrument panel (usually a white and black wire with a green connector). Run a jumper wire from the lead to ground.

On the CCC System, locate the test terminal under the instrument panel. Ground only the test lead. Use a jumper wire.

Ground the test lead or terminal according to the instructions given previously under "Troubleshooting."