DESCRIPTION
CCC is an electronically controlled exhaust emission system. It monitors several engine/vehicle functions and controls various operations, including the transmission torque converter clutch (TCC). The CCC system aids in the control of exhaust emissions while maintaining good fuel economy and driveability.
The Electronic Control Module (ECM) is the "brain" of the CCC system. The ECM controls engine systems to maintain good vehicle performance under all normal driving conditions.
The primary objective of the system is to maintain an ideal air/fuel ratio of 14.7:1. With this ratio maintained, the catalytic converter can effectively control nitrogen oxides (NOx), hydrocarbons (HC) and carbon monoxide (CO).
Schematic of Computer Command Control All components shown are not used on all engines. Scheme 1
SYSTEM OVERVIEW
The CCC system consists of the following sub-systems: Fuel Control, Data Sensors, Electronic Control Module (ECM), Spark Timing, Emission Control, Torque Converter Clutch (TCC), Diagnostic System and Catalytic Converter.
FUEL CONTROL OPERATION
California vehicles are equipped with "feedback" carburetors. These carburetors contain an electrically operated mixture control (M/C) solenoid. The M/C solenoid operates single or dual metering rods in the float bowl of the carburetor.
A metering rod supplements fuel supply to idle and main systems, varying air/fuel ratio within a pre-calibrated range. The M/C solenoid also controls air/fuel ratio through use of an idle air bleed circuit that operates in conjunction with the metering rod(s).
The ECM reacts to input from data sensors by constantly adjusting air/fuel mixture to maintain efficient engine performance. ECM controls M/C solenoid by providing a ground for solenoid.
When solenoid is energized, fuel flow through carburetor is reduced, providing a leaner mixture. When solenoid is de-energized, fuel flow through carburetor is increased, providing a richer mixture. The solenoid cycles (turns on and off) 10 times per second.
During closed loop operation, the ECM adjusts fuel mixture in response to signals received from the oxygen sensor. Under certain operating conditions, the ECM may ignore inputs from some sensors and substitute pre-programmed data to operate the engine.
During cold engine starts (engine speed below 200 RPM), M/C solenoid is turned off by the ECM. This provides a rich mixture to the engine. Under certain operating conditions, the ECM ignores oxygen sensor signals. When these conditions exist, the CCC system then operates in open loop mode.
DATA SENSORS OPERATION
Each sensor sends electrical impulses to ECM. The ECM computes ideal spark timing and fuel mixture ratio based on these signals. The function of each sensor is closely related to that of the other sensors. Operation of each sensor is as follows
Oxygen Sensor
The oxygen sensor is mounted in the engine exhaust stream. It supplies a low voltage (under .2 volt) when fuel mixture is lean (high oxygen content). When the fuel mixture is rich (low oxygen content), a higher voltage (up to 1 volt) will be supplied to the ECM. Oxygen sensor temperature must be over 600°F (316°C) to function properly.
Oxygen sensor measures quantity of oxygen only. On occasion, the oxygen sensor may cool off during idle, causing the CCC system to go into open loop mode. Running the engine at fast idle will warm up the oxygen sensor. Proper operation of the oxygen sensor requires the use of unleaded fuel only.
Oxygen sensor voltage output should not be measured. Current drain from voltmeter can cause permanent damage to sensor, shift sensor calibration range, and/or render sensor unusable. Do not connect jumper wire, test leads or other electrical connectors to sensor. Use these devices on ECM side of harness only, after disconnecting harness from sensor.
Coolant Temperature Sensor (CTS)
The CTS is located in the engine coolant stream. It supplies coolant temperature information to the ECM. The sensor has a high resistance (around 100,000 ohms) when coolant temperature is cold and a low resistance (under 1,000 ohms) when the coolant is warm.
The sensor sends engine temperature information to the ECM. This information is used to accomplish the following
- To vary air/fuel ratio as the coolant temperature varies with time during a cold start.
- To accomplish various switching functions at different temperatures on Early Fuel Evaporation (EFE), AIR Management Systems and Torque Converter Clutch (TCC).
- To vary spark advance.
Vacuum Sensor
The vacuum sensor is mounted in the engine compartment. This sensor signals the ECM of changes in manifold pressure (vacuum). The ECM uses these signals to adjust air/fuel mixture and spark timing.
Throttle Position Sensor (TPS)
This sensor is mounted on the carburetor. It is actuated by the accelerator pump linkage. The TPS is a variable resistor, similar to a fuel tank sending unit. It signals the ECM of changes in throttle blade position from closed to wide open throttle.
Park/Neutral (P/N) Switch
This switch is connected to transmission gear selector. It is closed when selector is in "P" or "N" positions and open when selector is in gear.
ELECTRONIC CONTROL MODULE (ECM) OPERATION
The ECM is located under the passenger seat on "G" series vans. On all other models, the ECM is located inside the instrument panel, near the glove box. It controls the CCC system by constantly monitoring and adjusting engine operation. The ECM also monitors distributor reference pulses to measure engine RPM and to determine spark timing.
Information concerning cooling system temperature, crankshaft RPM, throttle blade position, manifold pressure and amount of oxygen in exhaust gases is continuously fed into the ECM while the engine is running. The ECM is designed to process this data sensor information, and programmed to send the electrical responses necessary to control the CCC system.
The ECM contains an engine calibration unit called a PROM. The PROM is located under an access cover within the ECM. The PROM contains specific instructions to tailor each ECM to individual vehicle design. Information such as vehicle size and weight, transmission, engine and final drive ratio are contained within the PROM. A PROM that is programmed for a particular vehicle cannot be used on another vehicle that does not have the same standards.
ELECTRONIC SPARK TIMING
The Electronic Spark Timing (EST) system uses an HEI distributor with a 7-terminal HEI module. The distributor has no provision for vacuum or centrifugal advance. The HEI distributor communicates a reference pulse (indicating engine RPM) to the ECM via a 4-terminal connector. The ECM determines the proper spark advance for engine operating conditions, then sends an "EST" pulse to the distributor.
The ECM controls spark advance under normal operating conditions. Under certain operating conditions such as cranking, or when setting base timing, the distributor can operate without ECM control. This operating condition is called the by-pass mode. It is determined by the by-pass lead from the ECM to the distributor. When the by-pass lead is 5 volts, the ECM will control the spark. When the by-pass lead is grounded or open-circuited, the HEI module will control the spark.
Disconnecting the 4-terminal EST connector causes the engine to operate in the by-pass mode. It will also cause trouble code 41 to be set in the memory. Use the by-pass mode when setting base timing. After setting base timing, clear trouble code 41 from the memory.
EMISSION CONTROL OPERATION
The ECM electrically controls the following emission systems: AIR Management (AIR), Early Fuel Evaporation (EFE), and Exhaust Gas Recirculation (EGR). A brief description of each system follows
Air Management System
This system helps to reduce HC and CO content in exhaust gases and to quickly heat up catalytic converter and oxygen sensor during cold engine operation. This is accomplished by injecting air into exhaust port of each cylinder.
The ECM energizes an air control solenoid which permits air flow to air switching valve, directing air to exhaust ports. During warm engine (closed loop) operation, the ECM de-energizes air switching valve. This directs air to dual-bed converter, which lowers HC and CO emissions.
If air control valve detects rapid increase in manifold vacuum (deceleration condition), or ECM detects any failure in CCC system, air is diverted to air cleaner or dumped into atmosphere.
Exhaust Gas Recirculation (EGR)
The ECM controls ported vacuum to EGR valve with an electrically operated EGR bleed solenoid. When engine is cold, solenoid is energized, blocking vacuum to EGR valve. When engine is warm, solenoid is de-energized and EGR operation is allowed. The solenoid decreases ported vacuum to the EGR valve when the torque converter clutch is applied.
CATALYTIC CONVERTER
Proper emission control is accomplished with a special 3-way catalytic converter which converts all 3 major pollutants. The converter is a dual-bed type. The "upstream" section of the converter contains a reducing/oxidizing bed to reduce NOx while at the same time oxidizing HC and CO.
An air supply pipe from the AIR system introduces air between the dual beds (during closed loop operation) so the second bed can oxidize any remaining HC and CO with a high conversion efficiency, to minimize overall emissions.
TORQUE CONVERTER CLUTCH (TCC)
The ECM controls a solenoid (mounted on Auto. Trans.) which allows torque converter to directly connect engine to transmission. When vehicle speed is high enough, within specified engine temperature, load and at relatively constant throttle, ECM energizes TCC solenoid and engine is mechanically coupled to transmission.
When operating conditions indicate that transmission should operate as a normal fluid-coupled transmission, (during rapid acceleration or deceleration), solenoid is de-energized. The transmission also returns to normal automatic operation when brake pedal is depressed.
On 4-wheel drive models, a relay is installed between the torque converter clutch solenoid and the ECM. When the vehicle is in 4-wheel drive, the relay opens and the transmission will operate as a fluid coupled transmission through 2nd and 3rd gear operation. In 4th gear, the torque converter mechanically couples.
DIAGNOSTIC SYSTEM OPERATION
The ECM of the CCC system is equipped with a self-diagnosis system which detects system failures. When a malfunction occurs, the amber "CHECK ENGINE" light on the instrument panel comes on and a corresponding trouble code is stored in ECM memory. Malfunctions are recorded as either "hard failures" or "intermittent failures".
"Hard failures" cause "CHECK ENGINE" light to come on, and stay on, until malfunction is repaired. When "CHECK ENGINE" light remains on during vehicle operation, cause of malfunction MUST be determined.
"Intermittent failures" cause light to flicker and/or go out, 10 seconds after fault goes away. However, associated trouble code will be retained in ECM memory. "Intermittent failures" may be sensor related. If a sensor fails, ECM will use a substitute value in its calculations to continue engine operation.
In this condition, service is not mandatory, but driveability may suffer. If same or similar fault does not repeat within 50 ignition cycles, related trouble code will be erased from ECM memory.
As a bulb and system check, the "CHECK ENGINE" light will glow with ignition switch "ON" and engine not running. When engine is started, light should go out within 4 seconds. If not, a malfunction has been detected in CCC system.
Note. Different codes require different time intervals to set. Some codes set in as little as 5 seconds, while others may require that the related sensor or switch operate for 5 minutes or longer.
Note. For more Testing information, refer to the appropriate CODE TESTS article in this section. For more Trouble Shooting information, see the CCC TESTS W/O CODES article in this section.