Ccc Theory/operation Buick Electra VI

MODEL IDENTIFICATION

Repair procedures in this article are identified by body type. The following table lists the General Motors division, model name, and body type for 1983-to-1987 year models.

MODEL IDENTIFICATION

FUEL SYSTEM IDENTIFICATION

The following table lists the systems used with each engine.

SYSTEM IDENTIFICATION

DESCRIPTION

Note. Most Computer Command Control (CCC) problems are the result of mechanical breakdowns, poor electrical connections or damaged vacuum hoses. Before considering the CCC system as a possible cause of problems, ignition high tension wires, fuel supply, electrical connections and vacuum hoses should be checked. Failure to do so may result in lost diagnostic time.

The Computer Command Control (CCC) system used on General Motors vehicles monitors as many as 19 engine/vehicle functions. This system controls engine operation and lowers exhaust emissions while maintaining good fuel economy and driveability. The Electronic Control Module (ECM) is the "brain" of the CCC system. The ECM controls as many as 12 engine related systems constantly adjusting engine operation.

The CCC system is primarily an emission control system, designed to maintain a 14.7:1 air/fuel ratio under all operating conditions. When the ideal air/fuel ratio is maintained, the catalytic converter can control oxides of nitrogen (NOx), hydrocarbon (HC) and carbon monoxide (CO) emissions.

SYSTEM OVERVIEW

The CCC system consists of the following sub-systems: Fuel Control, Data Sensors, Electronic Control Module (ECM), Spark Timing, Idle Air Control (IAC) system, AIR Management, Emission Control, Torque Converter Clutch (TCC), Diagnostic System and Catalytic Converter.

ECM OPERATING CONDITIONS SENSED

1. A/C "ON" or "OFF"
2. Engine Coolant Temperature
3. Ambient Temperature
4. Barometric Pressure (BARO)
5. Brake "ON" or "OFF"
6. Cruise Control "ON" or "OFF"
7. Differential Pressure (Engine Vacuum)
8. Distributor Reference: Crankshaft Position & Engine Speed
9. EGR Vacuum
10. Engine Cranking
11. Engine Detonation (ESC)
12. Exhaust Oxygen (O2)
13. Manifold Absolute Pressure (MAP)
14. Mass Air Flow (MAF)
15. Manifold Air Temperature (MAF)
16. Park/Neutral Switch Position (P/N)
17. System Voltage
18. Throttle Position (TPS)
19. Transmission Gear Position
20. Vehicle Speed (VSS)

ECM OPERATING SYSTEMS CONTROLLED

1. A/C
2. Air Management
3. Canister Purge
4. Diagnostics: Check Engine Light, Data Output (ALCL) & Diagnostic Test Terminal (ALCL)
5. Early Fuel Evaporation (EFE)
6. Electric Fuel Pump
7. Electronic Fuel Injection (TBI & Port)
8. Electronic Spark Control (ESC)
9. Electronic Spark Timing (EST)
10. Engine Cooling Fan
11. Exhaust Gas Recirculation (EGR)
12. Fuel Control (M/C solenoid)
13. Hood Louvre
14. Idle Air Control (IAC)
15. Idle Speed (ISC. ILC ISS)
16. Transmission Converter Clutch (TCC)
17. Turbo Wastegate

Schematic of Computer Command Control System. Scheme 1

FUEL CONTROL (CARBURETED MODELS)

Carbureted models are equipped with "feedback" carburetors with an electric mixture control (M/C) solenoid. The M/C solenoid operates single or dual metering rods in the float bowl. The metering rod system supplements fuel supplied by the idle and main systems in the carburetor. It varies the air/fuel ratio within a pre-calibrated range. The M/C solenoid also controls air/fuel ratio through the use of an idle air bleed operating in conjunction with metering rod(s).

Sectional View of Mixture Control Solenoid Note air bleed above main metering rod. Scheme 2

Throttle Body Injection

An electrically pulsed injector(s) is located in the intake manifold throttle body unit. The ECM controls the injector "on" time (pulse width) to provide the proper amount of fuel to the engine.

Port Fuel Injection

Electrically pulsed injectors are located in the intake manifold. These injectors are next to the intake valves in the cylinder head. The ECM controls the "on" time of each injector (pulse width) to provide the proper amount of fuel to the engine.

DATA SENSORS

Each sensor furnishes electronic impulses to the ECM. The ECM computes spark timing and air/fuel mixture ratio for proper engine operation.

Air Conditioner "On" Switch

The air conditioner "ON" switch is mounted in the air conditioner compressor. This switch signals the ECM when the air conditioner compressor clutch is engaged. The ECM uses this signal to adjust idle speed when air conditioner compressor clutch is engaged.

Barometric Pressure Sensor (BARO)

This sensor is mounted above the right kickpad. This sensor measures ambient or barometric pressures and signals ECM of pressure changes due to altitude and/or weather. This sensor may be used on engines equipped with MAP sensor. This sensor compensates for higher altitudes by grounding terminal "8". This causes the ECM to deliver a slightly leaner mixture. BARO sensor circuit problems may set Code 32.

Coolant Temperature Sensor (CTS)

The CTS is located in a coolant passage. The ECM sends a 5 volt signal to the CTS. This 5 volt signal is then reduced by the resistance of the CTS and a voltage signal goes back to the ECM. When coolant temperatures are low, CTS resistance is high and a low voltage signal is sent to the ECM. When coolant temperatures are high, CTS resistance is low and a higher voltage signal is sent to the ECM. A coolant sensor problem may set Code 14 or 15.

Crank Signal

The ECM looks at the starter solenoid to tell when the engine is cranking. It uses this information to tell when the car is in the starting mode. If this signal isn't present, car may be hard to start.

E-Cell Timer

The E-Cell timer signals the ECM when a predetermined number of engine operating hours have passed. These hours are about the same as the given number of miles driven. The purpose of the E-Cell timer is to "re-tune" the engine after a predetermined number of miles have been driven.

High Gear Switch

The high gear switch is used on automatic transmissions. This switch is open in high gear (3rd or 4th) and closes when the transmission shifts into any other gear. High gear switch information is used to control emission control components.

Mass Air Flow Sensor (MAF)

The MAF sensor measures the flow of air entering the engine. The ECM uses this information to control fuel delivery. The MAF sensor produces a frequency signal that cannot be easily measured in testing. The sensor can be diagnosed by using procedures outlined in Code 33 and 34 charts.

Manifold Absolute Pressure Sensor (MAP)

The MAP sensor measures changes in manifold pressure (vacuum). Changes in manifold pressure can result from engine load and speed changes. The MAP sensor converts these changes in manifold pressure into a voltage output signal to the ECM. The ECM can monitor these signals and adjust air/fuel ratio and ignition timing under various operating conditions. The sensor can be diagnosed by using procedures outlined in Code 33 and 34 charts.

Manifold Air Temperature Sensor (MAT)

The MAT sensor is a thermistor mounted in the intake manifold. Low air temperature produces a high resistance (100,000 ohms at -40°F/-40°C) while high temperature causes low resistance (70 ohms at 266°F/135°C). The ECM supplies a 5 volt reference signal to the sensor through a resistor in the ECM. By measuring the return voltage, the ECM knows the manifold air temperature. Failure in the MAT sensor circuit should set either a Code 23 or 25.

Oxygen Sensor (O2)

The O2 sensor is mounted in the exhaust system where it can monitor oxygen content of the exhaust gases. The oxygen content reacts with the O2 sensor to produce a voltage output signal. This voltage signal is low (about .1 volt) when a lean mixture is present and high (about .9 volt) when a rich mixture is present.

When the ECM reads the voltage signal from the O2 sensor, the ECM will alter commands to the injector to produce either a leaner or richer mixture. The O2 sensor does not function until its temperature reaches 600°F (316°C). A problem in the O2 sensor circuit may set a Code 13.

Park/Neutral Switch (P/N)

This switch is connected to the transmission gear selector. The switch indicates when the transmission is in Neutral or Park. Information from the P/N switch is used for ignition timing control, the torque converter clutch and idle air control valve operation.

Throttle Position Sensor (TPS)

The TPS is a variable resistor connected to the throttle shaft on the TBI unit. The TPS has 3 wires connected to it. One is connected to a 5 volt supply voltage from the ECM, one is connected to ground and the other is connected to the ECM to send voltage signals according to throttle position. The voltage signal from the TPS varies from closed throttle to wide open throttle. A problem in the TPS circuit may set a Code 21 or 22.

Vacuum Sensor

Vehicles not equipped with a MAP sensor may be equipped with a vacuum sensor. Vacuum sensor also measures the difference between atmospheric pressure (outside air) and manifold pressure (vacuum).

Vehicle Speed Sensor (VSS)

The VSS sends a pulsing 8-volt signal to the ECM, which the ECM converts into miles per hour. This sensor mainly controls the Torque Converter Clutch (TCC). The VSS circuit may be diagnosed by using the chart for Code 24.

ELECTRONIC CONTROL MODULE (ECM)

The ECM is located in the passenger compartment behind the right side of the instrument panel or behind the right side kick panel. The ECM consists of input/output devices, Central Processing unit (CPU), power supply and memories.

Input/Output Devices

These devices are an integral part of the ECM. They convert electrical signals, received by the ECM from the various engine sensors, into digital signals for use by the CPU.

Central Processing Unit (CPU)

Digital signals received by the CPU are used to perform all mathematical computations and logic functions necessary to deliver proper air fuel mixture. The CPU also calculates spark timing and idle speed information. The CPU commands operation of emission control, closed loop fuel control and the diagnostic system.

Power Supply

The main source of power for the ECM is from the battery, through the ignition circuit.

Memories

The 4 types of memories in the ECM are: Read Only Memory (ROM), Random Access Memory (RAM), Programmable Read Only Memory (PROM) and the fuel system CALPAC.

1. Read Only Memory (ROM) - The ROM is programmed information that can only be read by the ECM. The ROM program cannot be changed. If battery voltage is removed, ROM information will be retained.
2. Random Access Memory (RAM) - This memory is the decision making center for the CPU. It works like a calculator. Data sensor input, diagnostic codes and results of calculations are temporarily stored in the RAM memory. If battery voltage is removed from the ECM, all information stored in the memory is lost.
3. Programmable Read Only Memory (PROM) - This memory is factory programmed information, including engine calibration data, transmission, vehicle weight and rear axle ratio application. The PROM can be removed from the ECM. If battery voltage is removed, PROM information will be retained.
4. CALPAC - Fuel Injected models use a new type of ECM. This ECM uses a PROM and a device called a CALPAC. The CALPAC allows fuel delivery so the engine will run in case of a PROM or ECM failure. Any time the ECM is replaced, the PROM and the CALPAC must both be installed into the replacement ECM. If battery voltage is removed, CALPAC information will be retained.

HEI-EST

Most General Motors vehicles are equipped with a High Energy Ignition system with Electronic Spark Timing (HEI-EST). The distributor contains a 7-terminal HEI-EST control module. The distributor is connected to the EST system by means of a 4-wire connector, leading to the external electronic control module (ECM).

When engine speed reaches 600 RPM or more (about 5-15 seconds after starting), the ECM transmits a constant 5 volt signal to the distributor HEI-EST module. This changes the position of the by-pass switch in the HEI-EST module.

When this occurs, the pickup coil's signals no longer flow directly to the ignition coil. Instead, the RPM signals are routed to the ECM.

The Programmable Read Only Memory (PROM) portion of the ECM has a basic spark advance curve based on engine speed. Spark timing is calculated by the ECM whenever an ignition pulse is present. Spark advance is controlled only when the engine is running (not during cranking). Engine sensor values are used by the ECM to modify the PROM information, increasing or decreasing spark advance to achieve maximum performance with minimum emissions.

An Electronic Spark Control (ESC) system is also used on some models. There are 4 basic components to the ESC system: A detonation sensor, an HEI-EST distributor, an ESC controller, and the ECM.

When detonation (engine knock) occurs, the detonation sensor sends an electrical signal to the ESC controller. The ESC controller amplifies this signal and sends it to the ECM. The ECM then retards spark timing until the ECM no longer receives a signal from the detonation sensor, through the ESC controller.

Computer Controlled Coil Ignition (C(3)I)

The C(3)I system is used on 3.0L & 3.8L Turbo models with Sequential Fuel Injection. It consists of the ECM, ignition module, camshaft sensor, crankshaft sensor and connecting wires. This system uses a sealed 14 pin connector which goes directly to the ECM.

Each cylinder is paired with the cylinder opposite it in the firing order. These pairs are; 1-4, 5-2 and 6-3. Both cylinders are fired at the same time; the cylinder on compression and the cylinder on exhaust. The cylinder on exhaust requires little available voltage to arc. The remaining voltage is used by the cylinder on compression. There are 3 coils for a 6-cylinder engine. Spark distribution is timed by a signal from a Hall Effect crankshaft sensor. This signal is used by the ignition module to trigger each cylinder at the proper time.

The system also uses a Hall Effect camshaft sensor. This sensor provides the ECM with a voltage signal when the number 1 cylinder is on the compression stroke. This information is used to properly time the fuel injection and spark.

IDLE AIR CONTROL (IAC) VALVE

The IAC valve is mounted on the throttle body and controls the amount of by-pass air around the throttle plate. If engine RPM is too low, more air is by-passed around the throttle plate to increase engine RPM. If engine RPM is too high, less air is by-passed around the throttle plate to decrease engine RPM.

When the engine is idling, the proper position of the IAC valve is determined based on battery voltage, coolant temperature, engine load and engine RPM. If the IAC valve is disconnected or connected with the engine running, the IAC valve has to be reset. Reset of the IAC is accomplished by driving the vehicle over 35 MPH with the circuit properly connected.

IDLE SPEED CONTROL (ISC) (CARBURETED MODELS)

The ISC is a motor which opens or closes the throttle (in idle position), according to commands from the ECM. The ISC maintains low idle speeds while preventing stalling due to engine load. The base idle speed is programmed into ECM memory and is not adjustable.

When the engine is cold, ECM holds the throttle valve open for a longer period of time to provide faster warm-up. This function is by-passed when throttle is opened enough to bring TPS off its idle circuit.

Note. Not all engines are equipped with ISC system. Some may use an Idle Speed Solenoid (ISS) or an Idle Load Compensator (ILC) to control engine idle speed without ECM commands.

IDLE SPEED MODULE (2.0L TBI ENGINE - 1986-87)

The 2.0L engine uses an Idle Speed Module to help control engine idle speed. This module receives input from the power steering and A/C units. The module increases engine idle speed when the power steering line pressure exceeds a certain preset value. If the vehicle also has A/C, the switch will disconnect the compressor clutch when the steering line pressure exceeds the predetermined value.

EMISSION CONTROL

The ECM electrically controls the following emission control systems: The AIR Management System, the Exhaust Gas Recirculation (EGR) system, the Early Fuel Evaporation (EFE) system, the Catalytic Converter and the Evaporative Emission Control System (EECS).

Air Injection Reaction (AIR) Management System

This system helps reduce hydrocarbon (HC) and carbon monoxide (CO) exhaust emissions. It also heats the catalyst and oxygen sensor quickly during engine warm-up. This is accomplished by injecting air into the exhaust port or catalytic converter.

When the ECM energizes the air control valve, air is allowed to flow to the air switching valve. The air switching valve then directs this air to the exhaust port. During warm engine operation (closed loop), the ECM de-energizes the air control valve. This causes the air switching valve to direct air to the catalytic converter.

If the air control valve detects a rapid decrease in manifold vacuum (deceleration condition), or ECM detects any failure in the CCC system, air is diverted to the air cleaner or is dumped to the atmosphere.

Exhaust Gas Recirculation

The ECM controls ported vacuum to the EGR valve with a solenoid valve. The ECM uses coolant temperature, throttle position and manifold pressure to control vacuum solenoid operation. During cold engine operation and idle, the solenoid valve is grounded by the ECM. This blocks vacuum to the EGR valve. During warm engine operation and off idle speeds, the solenoid is not grounded and vacuum opens the EGR valve.

Note. Vehicles may use an integral EFE/EGR valve, TCC/EGR valve or an EFE/EGR/Canister Purge Valve.

Evaporative Emission Control System (EECS)

This system controls purging of the vapor canister. The ECM controls vacuum to the purge valve with a solenoid. When the engine is in open loop, the solenoid valve is energized. This blocks vacuum to the purge valve.

When the engine is in open loop above a preset RPM, the solenoid valve is de-energized, allowing vacuum to be applied to the purge valve. Fuel vapors are then drawn into intake manifold for burning.

Note. Some vehicles control canister purge operation through an integral EFE/EGR/Canister Purge Valve.

Catalytic Converter

The 3-way catalytic converter with a dual bed is used to reduce exhaust emissions. This type of converter can reduce hydro- carbons (HC), carbon monoxide (CO) and oxides of nitrogen (NOx).

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 injects air between the beds of the converter. This is so the second converter bed can oxidize any remaining HC and CO to efficiently reduce exhaust emissions.

Early Fuel Evaporation (EFE)

The ECM controls the EFE system using one of the following 2 methods: Vacuum operated valve and actuator, or ceramic heater grid located underneath carburetor primary bore. The vacuum operated valve and actuator is operated by a control solenoid mounted on the valve cover. This solenoid controls vacuum to EFE valve by an electric signal from the ECM.

The ceramic heater grid is part of the carburetor insulator. When the ignition is turned "ON" and the coolant temperature is low, voltage is applied to the EFE relay through the ECM, energizing EFE heater. When coolant temperature increases, ECM de-energizes EFE relay, which shuts off voltage to EFE heater.

Note. EFE may not be used on all vehicles. Some vehicles may incorporate EFE control through EGR or AIR systems.

TORQUE CONVERTER CLUTCH (TCC)

The ECM controls a solenoid mounted in the transmission to allow the torque converter to directly connect the engine to the transmission. When vehicle speed is high enough, the ECM energizes the TCC solenoid and the engine is mechanically connected to the transmission.

When operating conditions indicate that the transmission should operate as normal, the TCC solenoid is de-energized. This allows the transmission to return to normal automatic operation. The transmission will also return to normal automatic operation when the brake pedal is depressed.

DIAGNOSTIC SYSTEM

Note. A "CHECK ENGINE" lamp driver is installed in the wiring harness from ECM to the "CHECK ENGINE" lamp. This driver amplifies the power to the "CHECK ENGINE" lamp to reduce amperage draw on the battery.

The ECM of the CCC system is equipped with a self-diagnostic system which detects system failures or abnormalities. When a malfunction occurs, the ECM will light the Amber "CHECK ENGINE" lamp located on the instrument panel. When the malfunction is detected and the lamp is turned on, a corresponding trouble code will be stored in the ECM memory. Malfunctions are recorded as "hard failures" or as "intermittent failures".

1. Hard failures - cause the "CHECK ENGINE" lamp to glow and remain on until the malfunction is repaired. If the "CHECK ENGINE" lamp comes on and remains on during vehicle operation, the cause of the malfunction must be determined.
2. Intermittent failures - cause the "CHECK ENGINE" lamp to flicker or go out after about 10 seconds when the fault goes away. However, the corresponding trouble code will be retained in the ECM memory. "Intermittent failures" may be sensor related. If a sensor fails, the ECM will use a substitute value in its calculations to continue engine operation. In this condition, service is not mandatory; but loss of good driveability may be encountered. If the related fault does not reoccur within 50 engine restarts, the related trouble code will be erased from the ECM memory.

As a bulb and system check, the "CHECK ENGINE" lamp will glow when the ignition switch is turned on and the engine is not running. When the engine is started, the lamp should go out. If not, a malfunction has been detected in the CCC system.

Note. Trouble codes will be recorded at various operating times. Some codes require operation of that sensor or switch for 5 seconds; others require operation for 5 minutes or longer.