GM Chevy Mid-Size Cars 1964-1988 Repair Guide

Computer Command Control (CCC) System


See Figures 1, 2, 3, 4, 5 and 6

The CCC system, installed on all 1981 and later cars, is basically a modified and improved version of the C-4 system. Its main advantage over its predecessor is that it can monitor and control a large number of interrelated emission control systems.

This new system can monitor up to 15 various engine/vehicle operating conditions and then use this information to control as many as 9 engine related systems. The system is thereby making constant adjustments to maintain optimum vehicle performance under all normal driving conditions while at the same time allowing the catalytic converter to effectively control the emissions of NOx, HC and CO.

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Fig. Fig. 1: Computer Command Control (CCC) system components and wiring

In addition, the Electronic Control Module (ECM) contains a built in diagnostic system that recognizes and identifies possible operational problems and alerts the driver through a Check Engine (or Service Engine Soon) light in the instrument panel. The light will remain ON until the problem is corrected. The ECM also has built in back-up systems that, in most cases of operational problems, will allow for the continued operation of the vehicle in a near normal manner until the repairs can be made.

The CCC system has some components in common with the C-4 system, although they are not interchangeable. These components include the Electronic Control Module (ECM), which, as previously stated, controls many more functions than does it predecessor, an oxygen sensor, an electronically controlled variable mixture carburetor, a three-way catalytic converter, throttle position and coolant sensors, a Barometric Pressure (BARO) sensor, a Manifold Absolute Pressure (MAP) sensor and a Check Engine light in the instrument panel.

Components unique to the CCC system include the Air Injection Reaction (AIR) management system, a charcoal canister purge solenoid, EGR valve controls, a vehicle speed sensor (in the instrument panel), a transmission converter clutch solenoid (only on models with automatic transmission), idle speed control and Electronic Spark timing (EST).

The ECM, in addition to monitoring sensors and sending out control signals to the carburetor, also controls the following components or sub-systems: charcoal canister purge control, the AIR system, idle speed, automatic transmission converter lock-up, distributor ignition timing, the EGR valve, and the air conditioner converter clutch.

The EGR valve control solenoid is activated by the ECM in a fashion similar to that of the charcoal canister purge solenoid. When the engine is warm, the ECM de-energizes the solenoid and the vacuum signal is allowed to reach and open the EGR valve.

The Transmission Converter Clutch (TCC) lock is controlled by the ECM through an electrical solenoid in the automatic transmission. When the vehicle speed sensor in the dash signals the ECM that the car has attained the predetermined speed, the ECM energizes the solenoid which allows the torque converter to mechanically couple the engine to the transmission. When the brake pedal is pushed, or during deceleration or passing, etc., the ECM returns the transmission to fluid drive.

The idle speed control adjusts the idle speed to all particular engine load conditions and will lower the idle under no-load or low-load conditions in order to conserve fuel.

Not all engines use all systems. Control application may differ.

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Fig. Fig. 2: CCC components locations-229 V6 engine

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Fig. Fig. 3: CCC components locations-231 V6 engine

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Fig. Fig. 4: CCC components locations-231 V6 turbo engine

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Fig. Fig. 5: CCC components locations-V8 engines

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Fig. Fig. 6: CCC components locations-262 V6 engine


See Figures 7, 8, 9 and 10

The following explains how to activate the trouble code signal light in the instrument cluster in order to begin system troubleshooting. Because of the complexity of the system, this is not a complete C-4 or CCC system troubleshooting and isolation procedure.

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Fig. Fig. 7: Electronic Control Module (ECM) location

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

The following symptoms could indicate a possible problem area with the C-4 or CCC systems:

Stalling or rough idling when the engine is cold
Stalling or rough idling when the engine is hot
Poor gasoline mileage
Sluggish or spongy performance
Hard starting when engine is cold
Hard starting when the engine is hot
Objectionable exhaust odors
Engine cuts out
Improper idle speed (CCC only)

As a bulb and system check, the Check Engine (or Service Engine Soon) 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/codes by a series of flashes which translate as follows: When the diagnostic test lead (C-4) or terminal (CCC) under the instrument panel is grounded with the ignition in the ON position and the engine NOT running, the Check Engine light will flash once, pause, and then flash twice in rapid succession. This is a Code 12, which indicates that the diagnostic system is working. After a long pause, the Code 12 will repeat itself until the engine is started or the ignition switch is turned OFF . For fuel injected engines, the ECM will continue in diagnostic mode and flash any stored trouble codes as long as the engine is not running. Should the engine be started with the test terminal grounded, fuel injected vehicles will enter the field service mode.

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Fig. Fig. 8: The C-4 system diagnostic test lead is located above the ECM

Trouble code diagnosis on 4.3L TBI vehicles is almost identical to the carbureted CCC vehicles. The major difference is that to begin code flashing on fuel injected vehicles, the diagnostic connector terminals MUST be grounded while the engine is NOT running. Once the engine is running, the indicator light will flash for 30 seconds to 2 minutes indicating open loop operation. After the system enters closed loop operation, the light will indicate engine rich or lean operation. When the Service Engine Soon light is out, a lean signal is being indicated. When the light is on the ECM is receiving a rich oxygen sensor signal.

Whenever the engine is started, the Check Engine light will remain ON for a few seconds as a bulb and system check, then the lifht will 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 (with the engine running except for 4.3L TBI engines), the trouble code will flash (3) three times. If more than one problem is found, each trouble code will flash (3) three times and then change to the next one. Trouble codes will flash in numerical order (lowest code number to highest). The trouble code series will repeat themselves for as long as the test leads or terminal remains grounded.

For more information regarding the ECM and fuel injection system, refer to Fuel System of this information.

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). The entire circuit must then be checked, starting with the harness and the sensor. The ECM should always be the last component that is suspected because it is usually the most expensive and most difficult to test (if testing is even possible).

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Fig. Fig. 9: Early CCC system diagnostic test terminal (pre 1982), located under the left side of the instrument panel

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Fig. Fig. 10: Under dash terminal location-1982 and later CCC systems

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

In 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, it must still be evaluated. It must be determined if the fault is intermittent or if the engine must be operating under certain conditions (acceleration, deceleration, etc.) before the Check Engine light will come on. In some cases, certain trouble codes will not be recorded in the ECM until the engine has been operated at part throttle for at least 5 to 8 minutes.

Intermittent fault codes are often due to loose or damaged wiring and connectors. If an intermittent code is present, check the wiring for breaks or damage. Locate the wiring connectors and make sure they are not corroded and that they are properly engaged. Sometimes simply by grasping and wiggling a poor connection (while the engine is running) will set an intermittent code.

On the C-4 system, the ECM erases all trouble codes every time that the ignition is turned off. In the case of intermittent faults, a long term memory is desirable. This can be produced by temporarily connecting the orange connector/lead from terminal S of the ECM directly to the battery (or to a the CCC system, a trouble code will be stored until the terminal "R'' at the ECM has been disconnected from the battery for at least 10 seconds.

Activating Trouble Code Read Out

On the C-4 system, activate the trouble code read out by grounding the trouble code test lead. Use the illustrations to help you locate the test lead under the instrument panel (usually a white and black wire and/or a green connector).

On the CCC system, locate the multi-terminal test connector under the left side of the instrument panel. Use a jumper wire and ground the test terminal (2nd terminal from the top right of the connector). This can be easily accomplished by jumpering the test terminal to the connector ground terminal (top right terminal). Remember that on carbureted vehicles the read out can only be activated while the engine is running, while on fuel injected vehicles, the read out can only be activated when the engine is stopped.

Ground the test lead/terminal according to the instructions given previously in the Basic Troubleshooting section.