Engine Controls - Theory & Operation Chevrolet Camaro IV

INTRODUCTION

This article covers basic description and operation of engine performance-related systems and components. Read this article before diagnosing vehicles or systems with which you are not completely familiar.

TERMINOLOGY

Due to Federal government requirements, manufacturers may use names and acronyms for systems and components different than those used in previous years. The following table will help eliminate confusion when dealing with these components and systems. Only relevant components and systems whose names have changed from current General Motors Corp. terminology have been listed.

SAE TERMINOLOGY

Mass Airflow (MAF)

MAF sensor measures flow of air entering the engine in grams per second. This measurement of airflow is a reflection of engine load (throttle opening and air volume), similar to the relationship of engine load to MAP or vacuum sensor signal. Mass Airflow (MAF) signal should remain relatively constant at cruise, gradually changing with throttle angle and rapidly changing on sudden acceleration. The PCM uses MAF information to control fuel delivery. Sensor produces a frequency signal which cannot be easily measured in testing (32-150 Hertz). This varying signal is proportional to airflow.

Speed Density

On models equipped with MAP and IAT sensors, the speed density method is used to compute the airflow rate. Manifold pressure and temperature are used to calculate the airflow rate to the PCM. The MAP sensor responds to manifold vacuum changes due to engine load and speed changes.

The PCM sends a voltage signal to MAP sensor. Manifold pressure changes result in resistance changes in MAP sensor. By monitoring MAP sensor output voltage, PCM determines manifold pressure. If MAP sensor fails, PCM will supply a fixed MAP value and use the TP sensor to control fuel.

COMPUTERIZED ENGINE CONTROLS

The computerized engine control system monitors and controls a variety of engine/vehicle functions. The computerized engine control system is primarily an emission control system which is designed to maintain a 14.7:1 air/fuel ratio under most operating conditions. When the ideal air/fuel ratio is maintained, the 3-way catalytic converter can control oxides of nitrogen (NOx), hydrocarbon (HC) and carbon monoxide (CO) emissions.

The computerized engine control system consists of the master controller (PCM), input devices (sensors and switches) and output signals.

POWERTRAIN CONTROL MODULE (PCM)

On most vehicles, PCM is located in passenger compartment. For exact location of PCM, see PCM LOCATION in appropriate TESTS W/CODES article or COMPONENT LOCATIONS in appropriate I - SYSTEM & COMPONENT TESTING article in the ENGINE PERFORMANCE section below. The PCM contains the Arithmetic Logic Unit (ALU), Central Processing Unit (CPU), power supply and system memories.

1. «TESTS W/CODES - 3.4L»(/chevrolet/camaro/iv-1992-1998/remont/testing-diagnostics/#engine-controls-tests-wcodes-34l)
2. «TESTS W/CODES - 5.7L»(/chevrolet/camaro/iv-1992-1998/remont/testing-diagnostics/#engine-controls-tests-wcodes-57l)
3. «SYSTEM/COMPONENT TESTS - 3.4L»(/chevrolet/camaro/iv-1992-1998/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-34l)
4. «SYSTEM/COMPONENT TESTS - 5.7L»(/chevrolet/camaro/iv-1992-1998/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-57l)

The PCM has a "learning" ability which allows it to make minor corrections for fuel system variations. If battery power to PCM is interrupted, a vehicle performance change may be noticed. This will correct itself and normal performance will return if vehicle is allowed to "relearn" optimum control conditions. This is accomplished by driving vehicle at normal operating temperature, under part throttle, moderate acceleration and idle conditions.

Arithmetic Logic Unit (ALU)

This internal component of the PCM converts electrical signals, received by PCM from various engine sensors, into digital signals for use by the CPU.

Central Processing Unit (CPU)

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

Power Supply

Power for PCM reference output signals (5 volts) and control devices (12 volts) is received from the battery (through ignition circuit when ignition switch is in ON position). Keep alive memory power is received directly from the battery.

Memories

PCM uses 3 types of memories: Read Only Memory (ROM), Random Access Memory (RAM) and Programmable Read Only Memory (PROM).

1. Read Only Memory (ROM)

ROM is programmed information that can only be read by PCM. The ROM program cannot be changed. If battery voltage is removed, ROM information will be retained.

1. Random Access Memory (RAM)

RAM is the scratch pad for the CPU. Data input, diagnostic codes and results of calculations are constantly updated and temporarily stored in RAM. If battery voltage is removed from PCM, all information stored in RAM is lost.

1. Programmable Read Only Memory (PROM)

PROM is factory programmed engine calibration data which "tailors" PCM for specific transmission, engine, emission, vehicle weight and rear axle ratio applications. The PROM can be removed from PCM. If battery voltage is removed, PROM information will be retained. An Electronically Erasable Programmable Read Only Memory (EEPROM) is used on some models. This is the same as a PROM except it can be electronically reprogrammed by the manufacturer using special equipment.

1. Electronically Erasable Programmable Read Only Memory (EEPROM)

Some models may use an EEPROM. This is the same as a PROM except it can be electronically reprogrammed by the manufacturer using special equipment.

Note. Components are grouped into 2 categories. The first category covers INPUT DEVICES, which control or produce voltage signals monitored by the control unit. The second category covers OUTPUT SIGNALS, which are components controlled by the control unit.

INPUT DEVICES

Vehicles are equipped with different combinations of input devices. Not all devices are used on all models. To determine the input devices used on a specific model, see appropriate wiring diagram in WIRING DIAGRAMS section. The available input signals include the following

A/C Request Signal

The air conditioner mode selector is mounted on instrument panel. This mode selector provides a simple "A/C request" signal which is monitored by the PCM. PCM uses this signal to determine control of A/C clutch relay (if equipped) and to adjust idle speed when A/C compressor clutch is engaged. On some models, PCM may also activate electric cooling fan when this signal is present. If this signal is not present on A/C-equipped vehicles, vehicle may idle rough when A/C compressor cycles. To check function of the A/C mode selector, perform functional check of A/C mode selector. See appropriate I - SYSTEM & COMPONENT TESTING article in the ENGINE PERFORMANCE section below.

1. «SYSTEM/COMPONENT TESTS - 3.4L»(/chevrolet/camaro/iv-1992-1998/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-34l)
2. «SYSTEM/COMPONENT TESTS - 5.7L»(/chevrolet/camaro/iv-1992-1998/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-57l)

A/C Pressure Sensor

Some models are equipped with an air conditioner pressure sensor which is used to inform PCM of A/C system pressure. PCM uses this signal to determine A/C compressor load on the engine to control idle speed with IAC valve. Failure in A/C pressure sensor circuit or with A/C pressure sensor should set a related diagnostic trouble code and A/C compressor clutch will become inoperative. A fixed high pressure value will exist if the ground circuit to sensor is faulty. For testing procedures, see appropriate TESTS W/CODES article in the ENGINE PERFORMANCE section below.

1. «TESTS W/CODES - 3.4L»(/chevrolet/camaro/iv-1992-1998/remont/testing-diagnostics/#engine-controls-tests-wcodes-34l)
2. «TESTS W/CODES - 5.7L»(/chevrolet/camaro/iv-1992-1998/remont/testing-diagnostics/#engine-controls-tests-wcodes-57l)

A/C Pressure Switches

A/C high and low pressure switches may be used in the PCM-monitored A/C request signal circuit. Switches are normally closed, completing the circuit between ignition and PCM. PCM will engage or disengage A/C clutch relay based upon status of this circuit. When system refrigerant pressure increases beyond a certain point, high side switch will open, causing A/C request line voltage to drop. If system refrigerant level decreases, causing refrigerant pressure to drop below normal, low side pressure switch will open, once again causing A/C request line voltage to drop. Switches may be used as normal clutch cycling devices or as safety devices which prevent compressor damage in the event of excessively high or low refrigerant pressure.

A/C Temperature Sensors

Air conditioner high side and low side temperature sensors inform PCM of A/C system temperature levels. Low temperature signal will cause A/C compressor to disengage. High temperature levels help PCM determine control of A/C compressor relative to cooling fans and idle speed.

Battery Voltage

Battery voltage is monitored by PCM. If battery voltage swings low, a weak spark or improper fuel control may result. To compensate for low battery voltage, PCM may increase idle speed, advance ignition timing, increase ignition dwell or enrich the air/fuel mixture. If voltage swings excessively high or low, PCM may set a charging system diagnostic trouble code and illuminate the Malfunction Indicator Light (MIL).

Brake Switch Feedback

Models equipped with cruise control systems may monitor the brake switch circuit to determine when to engage and disengage cruise control. On vehicles equipped with a Torque Converter Clutch (TCC), one circuit of brake switch is in series with the power supply for the TCC solenoid located in the transmission/transaxle.

Camshaft Position Sensor (3.4L)

On 3.4L (VIN S), camshaft position sensor is located on timing cover, behind water pump, near camshaft sprocket. As the camshaft sprocket turns, a magnet in it activates a Hall Effect switch in camshaft position sensor. This signal is generated whenever cylinder No. 1 is at TDC of its compression stroke.

This signal is used by PCM, in conjunction with the crankshaft position sensor and crankshaft sensor signals, to trigger the fuel injectors in sequential firing order. If sensor should fail while engine is running, engine will continue to run using the last calculated camshaft sensor signal to maintain sequential fuel injection mode. Upon restart, engine will run with a one in 6 chance of being correct.

Crankshaft (3X) Sensor (3.4L)

The 3X signal is generated by a PM generator crankshaft sensor which is mounted in the side of the engine block. See CRANKSHAFT POSITION SENSOR. The 3X signal is passed on to the PCM and is also used by the ignition control module to determine which ignition coil to fire.

Crankshaft (24X) Sensor (3.4L)

The 24X signal is generated by a Hall Effect switch located in an aluminum mounting bracket and bolted to the front left side of the engine timing chain cover. The Hall Effect switch alternately grounds and opens a PCM-monitored, 12-volt circuit. An air gap separates the Hall Effect switch from a magnet. An interrupter ring containing 24 blades and spaces is mounted on the vibration damper and rotates with the crankshaft.

When the Hall Effect switch is shielded from the magnetic field generated by the magnet by one of the interrupter blades, the 12-volt, PCM-monitored circuit is not grounded by the Hall Effect switch. When the Hall Effect switch is exposed to the magnetic field, the 12-volt, PCM-monitored circuit is grounded by the Hall Effect switch. The constant grounding and opening of this circuit results in an ON-OFF signal which the PCM interprets as RPM (engine speed).

Crankshaft Position Sensor

Crankshaft position sensor, used on 3.8L, utilizes a Hall Effect switch mounted near vibration damper. Sensor monitors vibration damper position (crankshaft position) and sends signals to ignition control module. These signals provide PCM with a TDC position reference for each piston, as well as supplying an engine speed (RPM) signal.

The 3.4L Direct Ignition System (DIS) crankshaft position sensor protrudes through side of engine block to within .05" (1.3 mm) of an internally-mounted crankshaft reluctor ring. The reluctor ring is a special trigger wheel cast into the crankshaft. As crankshaft rotates, notches in reluctor ring change the magnetic field at the tip of the position sensor. This creates an induced AC voltage signal in the sensor windings, resulting in reference signals which are sent to PCM by ignition control module. This allows PCM to compute crankshaft position and RPM and fire appropriate ignition coil at the proper time.

Engine Coolant Temperature (ECT) Sensor

The ECT sensor is a thermistor (temperature sensitive resistor) located in an engine coolant passage. The PCM supplies and monitors a 5-volt signal to ECT sensor through a resistor in PCM. This monitored 5-volt signal is then reduced by resistance of the engine coolant temperature. When coolant temperatures are low, ECT sensor resistance is high, and a high monitored voltage signal is seen by the PCM. When coolant temperatures are high, ECT sensor resistance is low, and a low monitored voltage is seen by the PCM. After engine startup, temperature should rise steadily to proximately 194°F (90°C), then stabilize when thermostat opens.

Engine coolant temperature signal is used in the control of most systems the PCM controls (i.e. fuel delivery, ignition timing, idle speed, emission control devices). After a vehicle has been parked overnight, ECT and IAT sensor signals (resistance and temperature) should be close to same reading. An ECT sensor which is out of calibration will not set a diagnostic trouble code but will cause fuel delivery and driveability problems. Failure in ECT sensor circuit (open or short to ground) will cause monitored voltage to swing high or low and should set a related diagnostic trouble code.

Fuel Pump Feedback

On some models, the fuel pump circuit between the fuel pump relay and fuel pump is monitored by PCM. This enables PCM to determine when the fuel pump relay is energized and voltage is being delivered to fuel pump. Voltage monitored on this circuit is also used in calculations to determine changes in idle speed, air/fuel ratio and ignition dwell. Failure in this monitored circuit should set a related diagnostic trouble code.

Gear Switches

Gear switches are located inside automatic transmission. Switches may be normally open or closed and change status depending upon internal hydraulic pressures. High gear switch information is used by PCM in controlling emission components and engagement of Torque Converter Clutch (TCC).

Ignition/Crank Signal

The PCM monitors initial cranking (RPM) signal to determine when the engine is being started. This information is used for starting enrichment. If this signal is intermittent or not available, hard starting or a no-start condition will result.

Intake Air Temperature (IAT) Sensor

The IAT sensor is a thermistor (temperature sensitive resistor) mounted in the intake manifold. The PCM supplies and monitors a 5-volt signal to IAT sensor through a resistor in PCM. This monitored 5-volt signal is then reduced by resistance of the intake air temperature. Low intake air temperature produces high resistance, while high intake air temperature produces low resistance. By monitoring this voltage, PCM determines manifold air temperature. IAT sensor signal is used to adjust spark timing according to incoming air density.

Intake air temperature should read close to ambient temperature with engine cold, and rise as underhood temperature increases. After a vehicle has been parked overnight, IAT and ECT sensor signals (resistance and temperature) should be close to same reading. An IAT sensor which is out of calibration will not set a diagnostic trouble code but will cause fuel delivery and driveability problems. Failure in IAT sensor circuit (open or short to ground) will cause monitored voltage to swing high or low and should set a related diagnostic trouble code.

Knock Sensor

The knock sensor is a piezoelectric device which detects abnormal engine vibrations (spark knock) in the engine. This vibration results in the production of a very low AC signal which is sent from the knock sensor back to knock sensor module, if equipped (mounted on PCM), or to the EEPROM/PROM portion of PCM on models not equipped with a knock senor module. The PCM will then retard spark timing until engine knock ceases. Some models use 2 knock sensors.

For additional information on knock sensor operation, see KNOCK SENSOR OPERATION under IGNITION TIMING SYSTEMS under IGNITION SYSTEM. Failure in knock sensor circuit should set a related diagnostic trouble code. If a related diagnostic trouble code is not present and the knock sensor system is suspected as the cause of a driveability problem, perform a functional check of the knock sensor. See appropriate I - SYSTEM & COMPONENT TESTING article in the ENGINE PERFORMANCE section below.

1. «SYSTEM/COMPONENT TESTS - 3.4L»(/chevrolet/camaro/iv-1992-1998/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-34l)
2. «SYSTEM/COMPONENT TESTS - 5.7L»(/chevrolet/camaro/iv-1992-1998/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-57l)

Manifold Absolute Pressure (MAP) Sensor

The MAP sensor measures changes in manifold pressure. Changes in manifold pressure result from engine load and speed changes. The MAP sensor converts these changes in manifold pressure into a voltage output signal to PCM (about 1.5 volts at idle to about 4.5 volts at WOT). The PCM can monitor these signals and adjust air/fuel ratio and ignition timing under various operating conditions.

If MAP sensor fails, the PCM will substitute a fixed MAP value and will use the TP sensor to control fuel delivery. Failure in MAP sensor circuit should set a related diagnostic trouble code. If a related diagnostic trouble code is not present and MAP sensor is suspected of causing a driveability problem, perform a functional check of MAP sensor. See appropriate I - SYSTEM & COMPONENT TESTING article in the ENGINE PERFORMANCE section below.

1. «SYSTEM/COMPONENT TESTS - 3.4L»(/chevrolet/camaro/iv-1992-1998/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-34l)
2. «SYSTEM/COMPONENT TESTS - 5.7L»(/chevrolet/camaro/iv-1992-1998/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-57l)

Mass Airflow (MAF) Sensor

The MAF sensor measures flow of air entering the engine in grams per second. This measurement of airflow is a reflection of engine load (throttle opening and air volume), similar to the relationship of engine load to MAP or vacuum sensor signal. Mass Airflow (MAF) signal should remain relatively constant at cruise, gradually changing with throttle angle and rapidly changing on sudden acceleration. The PCM uses MAF information to control fuel delivery. Sensor produces a frequency signal which cannot be easily measured in testing (32-150 Hertz). This varying signal is proportional to airflow. Failure in MAF sensor circuit should set a related diagnostic trouble code.

Oxygen Sensor (O2S)

The oxygen sensor is mounted in the exhaust system where it monitors oxygen content of exhaust gases. Two oxygen sensors are used on some models. The oxygen content causes the Zirconia/Platinum-tipped oxygen sensor to produce a voltage signal which is proportional to exhaust gas oxygen concentration (0-3%) compared to outside oxygen (20-21%). This voltage signal is low (about .1 volt) when a lean mixture is present and high (about 1.0 volt) when a rich mixture is present. As PCM compensates for a lean or rich condition, this voltage signal constantly fluctuates between high and low, crossing a .45-volt reference voltage supplied by PCM on the oxygen sensor signal line. This is referred to as "cross counts."

The oxygen sensor will not function properly (produce voltage) until its temperature reaches approximately 600°F (316°C). On some models, oxygen sensor is equipped with a sensor heating element. This allows the sensor to reach operating temperature sooner and prevents fuel system from re-entering "open loop" mode due to a cooled sensor (which is a normal occurrence during prolonged idle).

At temperatures less than the normal operating range of the sensor, vehicle will function in "open loop" mode and PCM will not make air/fuel adjustments based upon oxygen sensor signals but will use TP sensor and MAP or MAF values to determine air/fuel ratio from a table built into memory. When PCM reads a voltage signal greater than .45 volt from the oxygen sensor, PCM will begin to alter commands to injector to produce either a leaner or richer mixture.

Once vehicle has entered "closed loop", a cooled-down sensor or a fault in the oxygen sensor circuit (open or shorted circuit) is the only thing which can return it to "open loop". Failure in oxygen sensor circuit should set a related diagnostic trouble code.

Park/Neutral Position (PNP) Switch

PNP switch is connected to transmission gear selector. PNP switch signals PCM when transmission is in Park, Neutral or Drive. Information from PNP switch is used by PCM for determining control of IAC valve, TCC and EGR. To check PNP switch, perform functional check of switch. See appropriate I - SYSTEM & COMPONENT TESTING article in the ENGINE PERFORMANCE section below. If vehicle is driven with PNP switch disconnected, idle quality will be affected and a possible false related diagnostic trouble code may be set.

1. «SYSTEM/COMPONENT TESTS - 3.4L»(/chevrolet/camaro/iv-1992-1998/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-34l)
2. «SYSTEM/COMPONENT TESTS - 5.7L»(/chevrolet/camaro/iv-1992-1998/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-57l)

Power Steering Pressure (PSP) Switch

The PSP switch informs PCM of engine load conditions that exist when steering wheel is turned from center to full lock position. PCM uses information to help control idle speed, and on some models, A/C clutch. To check PSP switch, perform functional check of switch. See appropriate I - SYSTEM & COMPONENT TESTING article in the ENGINE PERFORMANCE section below.

1. «SYSTEM/COMPONENT TESTS - 3.4L»(/chevrolet/camaro/iv-1992-1998/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-34l)
2. «SYSTEM/COMPONENT TESTS - 5.7L»(/chevrolet/camaro/iv-1992-1998/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-57l)

RPM Reference Signal

The RPM is monitored by PCM through tach/pulse signals (circuit No. 430) produced by either the ignition control module, (PM generator signal on DIS and IDI). These signals are used by PCM for determining control of timing, fuel delivery, EGR function and idle speed.

Throttle Position (TP) Sensor

The TP sensor is a variable mechanical resistor connected directly to the throttle shaft linkage. The TP sensor has 3 wires connected to it. One is connected to a 5-volt reference voltage supply from PCM, the second is connected to PCM ground and the third is the signal return which is monitored by PCM. The voltage signal from the TP sensor varies from closed throttle (.5-1.0 volt) to wide open throttle (4.5-5.0 volts). This signal is used by PCM for determining control of fuel, idle speed, spark timing and converter clutch. Failure in TP sensor circuit should set a related diagnostic trouble code.

Transmission Fluid Temperature Sensor (5.7L)

Transmission fluid temperature sensor is a thermistor (temperature sensitive resistor) and is located in valve body. High sensor resistance produces high signal input voltage which corresponds to low fluid temperature. Low sensor resistance produces low signal input voltage which corresponds to high fluid temperature. PCM uses transmission fluid temperature sensor signal to determine TCC apply and release schedules, hot mode determination and shift quality. Failure in transmission fluid temperature sensor circuit should set a related diagnostic trouble code.

Transmission Range Switch

Transmission range switch is mounted on transaxle assembly. Transmission range switch inputs to PCM indicate which gear is selected. Information from transmission range switch is used by PCM for determining control of IAC valve, timing and canister purge operation. To check transmission range switch, perform functional check of switch. See appropriate I - SYSTEM & COMPONENT TESTING article in the ENGINE PERFORMANCE section below. If vehicle is driven with transmission range switch disconnected, idle quality will be affected and a possible false related diagnostic trouble code may be set.

1. «SYSTEM/COMPONENT TESTS - 3.4L»(/chevrolet/camaro/iv-1992-1998/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-34l)
2. «SYSTEM/COMPONENT TESTS - 5.7L»(/chevrolet/camaro/iv-1992-1998/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-57l)

Vehicle Speed Sensor (VSS)

VSS is a Permanent Magnet (PM) generator mounted in transaxle/transmission. The VSS sends a pulsing AC voltage signal to PCM, which PCM converts into miles per hour (MPH). VSS signal is used by PCM in controlling TCC and shift solenoids. Signal may also be used for instrument cluster speedometer and cruise control system. Failure in VSS circuit should set a related diagnostic trouble code.

OUTPUT SIGNALS

Note. Vehicles are equipped with different combinations of PCM-controlled components. Not all components listed below are used on every vehicle. For theory and operation on each output component, refer to system indicated after component.

A/C Compressor Clutch

See MISCELLANEOUS CONTROLS.

Air Injection System

See EMISSION SYSTEMS.

Canister Purge Control Solenoid

See EMISSION SYSTEMS.

Cooling Fan Relay

See MISCELLANEOUS CONTROLS.

Digital EGR Valve

See EMISSION SYSTEMS.

Direct Ignition System (DIS)

See IGNITION SYSTEM.

EGR Control Solenoid

See EMISSION SYSTEMS.

Electronic Variable Orifice (EVO) Actuator

See MISCELLANEOUS CONTROLS.

Fuel Injectors

See FUEL CONTROL.

Fuel Pump & Fuel Pump Relay

See FUEL DELIVERY.

High Energy Ignition Electronic Spark Timing (HEI-EST)

See IGNITION SYSTEM.

HOT Light Or Coolant Temperature (TEMP) Light

See MISCELLANEOUS CONTROLS.

Idle Air Control (IAC) Valve

See IDLE SPEED.

Integrated Direct Ignition (IDI)

See IGNITION SYSTEM.

Linear EGR Valve

See EMISSION SYSTEMS.

Knock Sensor Operation

See IGNITION SYSTEM.

Malfunction Indicator Light (MIL)

See SELF-DIAGNOSTIC SYSTEM.

Opti-Spark

See IGNITION SYSTEM.

Self-Diagnostics

See SELF-DIAGNOSTIC SYSTEM.

Serial Data

See SELF-DIAGNOSTIC SYSTEM.

Shift Light

See MISCELLANEOUS CONTROLS.

Shift Solenoids (Electronically-Controlled Auto Transmission)

See MISCELLANEOUS CONTROLS.

Torque Converter Clutch

See MISCELLANEOUS CONTROLS.

Fuel Pump

An in-tank electric fuel pump delivers fuel to injectors through an in-line fuel filter. The pump is designed to supply fuel pressure in excess of vehicle requirements. The pressure relief valve in the fuel pump controls maximum fuel pump pressure.

A pressure regulator, mounted in fuel rail keeps fuel available to injectors at a constant pressure. Excess fuel is returned to fuel tank through pressure regulator return line. For fuel pressure specifications, see SPECIFICATIONS article in the ENGINE PERFORMANCE section.

When the ignition switch is turned to ON position, PCM will turn on the electric fuel pump by energizing the fuel pump relay. The PCM will continue to energize relay if the engine is running or cranking (PCM is receiving reference pulses from the ignition control module). If no reference pulses exist, PCM de-energizes fuel pump relay within 2 seconds after ignition is turned on. For additional information, see FUEL PUMP RELAY.

Fuel Pump Relay

When ignition switch is turned to the ON position, PCM will turn on the electric fuel pump by energizing the fuel pump relay. PCM will keep relay energized if engine is running or cranking (PCM is receiving reference pulses from ignition control module). If no reference pulses exist, PCM turns pump off within 2 seconds after key on.

As a back-up system to fuel pump relay, fuel pump is also activated by the oil pressure switch. The oil pressure switch is normally open until oil pressure reaches approximately 4 psi (.28 kg/cm 2 ). If fuel pump relay fails, the oil pressure switch closes when oil pressure is obtained, operating the fuel pump. An inoperative fuel pump relay may result in extended cranking times due to the time required to build up oil pressure. Oil pressure switch may be combined into a single unit with an oil pressure gauge sender or sensor.

For additional information on fuel pump activation, see BASIC TESTING - 3.4L/5.7L and appropriate I - SYSTEM & COMPONENT TESTING TESTING articles in the ENGINE PERFORMANCE section below.

1. «SYSTEM/COMPONENT TESTS - 3.4L»(/chevrolet/camaro/iv-1992-1998/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-34l)
2. «SYSTEM/COMPONENT TESTS - 5.7L»(/chevrolet/camaro/iv-1992-1998/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-57l)

Fuel Pressure Regulator

Fuel pressure regulator is a diaphragm-operated relief valve with injector pressure on one side and manifold pressure (vacuum) on the other. Pressure regulator compensates for engine load by increasing fuel pressure when low manifold vacuum is experienced.

During periods of high manifold vacuum, regulator-to-fuel tank return orifice is fully open, keeping fuel pressure on the low side of its regulated range. As throttle valve opens, vacuum to regulator diaphragm decreases, allowing spring tension to gradually close off return passage. At wide open throttle, when vacuum is at its lowest, return orifice is restricted, providing maximum fuel volume and maintaining constant fuel pressure to injectors.

FUEL CONTROL

The PCM, using input signals, determines adjustments to the air/fuel mixture in order to provide the optimum ratio for proper combustion under all operating conditions. One type of fuel control system is used: port fuel injection. This system can operate in "open loop" or "closed loop" mode. Description of these modes is as follows

Open Loop

When engine is cold and engine speed is greater than 400 RPM, PCM operates in "open loop" mode. In "open loop", PCM calculates air/fuel ratio based upon inputs from Engine Coolant Temperature (ECT), Intake Air Temperature (IAT) and Manifold Absolute Pressure (MAP) sensors. Engine will remain in "open loop" operation until oxygen sensor reaches operating temperature, engine coolant temperature reaches preset temperature, and a specific period of time has elapsed after engine start-up.

Closed Loop

When oxygen sensor has reached operating temperature, engine coolant temperature has reached a preset temperature and a specific period of time has passed since engine start-up, PCM operates in "closed loop". In "closed loop", PCM controls air/fuel ratio based upon oxygen sensor signals (in addition to other input parameters) to maintain as close to a 14.7:1 air/fuel mixture as possible. If oxygen sensor cools off (due to excessive idling) or a fault occurs in the oxygen sensor circuit, vehicle will once again enter "open loop" mode.

Battery Voltage Correction

PCM compensates for low battery voltage by increasing injector pulse width, increasing idle RPM and increasing ignition dwell time. PCM is able to perform these commands because of a built-in memory/learning function.

Fuel Cut-Off

Injectors are de-energized when ignition is turned off to prevent dieseling. Injectors will not be energized if RPM reference pulses are not received by the PCM, even with ignition on. This prevents flooding before starting. Fuel cut-off will also occur at high engine RPM to prevent internal damage to engine. On some models, fuel injector signals may also be cut off during periods of high speed, closed throttle deceleration (when fuel is not needed).

Multiport Fuel Injection (MFI)

Individual, electrically pulsed injectors (one per cylinder) are located in intake manifold fuel rails. These injectors are next to intake valves in cylinder head.

Standard MFI systems feature simultaneous double-fire injection. Fuel injectors are pulsed once for each engine revolution, each spray providing 1/2 the fuel required for the combustion process. Thus, 2 injections of fuel (2 rotations of crankshaft) are mixed with incoming air to produce the fuel charge for each combustion cycle.

Some models use Sequential Fuel Injection (SFI). Injectors on these models are pulsed sequentially in spark plug firing order. The main differences between sequential and simultaneous systems are injectors, wiring and the PCM.

In all systems, constant fuel pressure is maintained to the injectors. Air/fuel mixture is regulated by amount of time injector stays open (pulse width). Various sensors provide information to the PCM to control pulse width.

IDLE SPEED

PCM controls engine idle speed based upon engine operating conditions. The PCM senses engine operating conditions and determines the best idle speed.

Idle Air Control Valve

The Idle Air Control (IAC) valve controls engine idle speed during engine load changes to prevent stalling. The IAC valve is mounted on throttle body or on upper manifold assembly, and controls the amount of air by-passed around the throttle plate. To control engine idle speed, the IAC valve moves its pintle in and out in steps referred to as "counts" (zero counts, fully seated; 255 counts, fully retracted). Counts can be measured using a scan tester plugged into the Data Link Connector (DLC).

Normal counts on an idling engine should be 4-60. When engine is idling, PCM determines proper positioning of IAC valve based on battery voltage, engine coolant temperature, engine load and engine RPM. If engine RPM is too low, pintle is retracted and more air is by-passed around the throttle plate to increase engine RPM. If engine RPM is too high, pintle is extended and less air is by-passed around the throttle plate to decrease engine RPM.

If IAC valve is disconnected or connected with engine running, IAC loses its reference point and has to be reset. Resetting of IAC is accomplished on some models by turning ignition on and off. On other models, driving vehicle at normal operating temperature and speed greater than 35 MPH with circuit properly connected may be necessary. Problems in IAC circuit should set a related diagnostic trouble code.

The IAC valve affects only the idle system. If valve is stuck fully open, excessive airflow into the manifold creates a high idle speed. Valve stuck closed allows insufficient airflow, resulting in low idle speed. For calibration purposes, several different design IAC valves are used. Ensure proper design valve is used during replacement.

IGNITION SYSTEM

All vehicles are equipped with a high energy ignition system capable of producing in excess of 50,000 volts.

DIRECT IGNITION SYSTEM (DIS) - 3.4L

DIS is a distributorless system used on 3.4L models. The operation of DIS is quite similar to operation of the C(3)I system. Systems consist 3 (V6) or 4 (V8) ignition coils, ignition control module (located under coil pack), a camshaft position sensor, 2 Hall Effect crankshaft position sensors, necessary wiring, and the ignition control and fuel metering portion of the PCM.

Spark is timed by a signal sent from a crankshaft position sensor mounted through side of engine block instead of from a crankshaft position sensor mounted at crankshaft pulley (such as C(3)I). This signal is received by PCM (through ignition control module) and is used to trigger each coil at the proper time. See CRANKSHAFT POSITION SENSOR under INPUT DEVICES. As with the C(3)I system, each cylinder is fired consecutively with the cylinder opposite it in the firing order. On V8, cylinder No. 1 is paired with No. 4, No. 2 with No. 5, No. 3 with No. 8 and No. 6 with No. 7. On V6, cylinder No. 1 is paired with No. 4, No. 2 with No. 5, and No. 3 with No. 6.

Crankshaft position sensor is mounted on bottom of ignition control module or near the ignition control module. The crankshaft position sensor protrudes through the side of engine block to within .05" (1.3 mm) of an internally-mounted crankshaft reluctor ring. Sensor position is not adjustable.

The reluctor is a piece of metal, cast with the crankshaft. Reluctor has 7 slots machined into it, 6 of which are equally spaced (60 degrees apart). The seventh slot is spaced about 10 degrees from one of the other slots and generates a synchronization pulse signal. As crankshaft rotates, notches in reluctor ring change the magnetic field at the tip of position sensor. This creates an induced AC voltage signal in the sensor windings, resulting in RPM reference signals which are sent to PCM by the ignition control module. This allows PCM to compute crankshaft position and RPM.

OPTI-SPARK (5.7L)

The PCM supplies and monitors two 5-volt reference signals to the Opti-Spark ignition control module inside of the sealed distributor, one on high resolution signal line (360 pulses per camshaft revolution) and one on low resolution signal line (8 pulses per camshaft revolution). Ignition control module will toggle these signals between zero and 5 volts as the camshaft turns. Camshaft-driven distributor is mounted behind water pump.

PCM uses these monitored reference signals in calculations used to control ignition timing. After computing necessary changes to ignition timing, PCM triggers ignition coil through the ignition coil driver. Unlike other type ignition systems, Opti-Spark does not use a by-pass circuit. Timing is always in EST mode.

By comparing the high and low resolution inputs, PCM can determine the position of cylinder No. 1 and TDC position. If either signal is missing, a diagnostic trouble code will set in PCM memory.

IGNITION TIMING SYSTEMS

Note. Unlike other type ignition systems, 5.7L with Opti-Spark do not use a by-pass circuit. Ignition timing on this system is constantly in EST mode.

Ignition Timing Advance

At engine speeds less than 400 RPM, the ignition control module controls spark advance by triggering coils at a predetermined interval based only on engine speed. At engine speeds greater than 400 RPM (EST mode), the PCM takes over control of the ignition timing.

PCM controls ignition timing based upon input signals from the engine RPM reference line (ignition control module), engine coolant temperature sensor, intake air temperature sensor, throttle position sensor, knock sensor, vehicle speed sensor, and the MAF or MAP sensor.

The PROM portion of the PCM has a programmed spark advance curve based on engine speed. Spark timing is calculated by PCM whenever an ignition pulse is present. Spark advance is controlled only when engine is running (not during cranking). Input signal values are used by PCM to modify PROM information, increasing or decreasing spark advance to achieve maximum performance with minimum emissions. To check ignition system operation, see BASIC TESTING - 3.4L/5.7L or I - SYSTEM & COMPONENT TESTING article in the ENGINE PERFORMANCE section below.

1. «SYSTEM/COMPONENT TESTS - 3.4L»(/chevrolet/camaro/iv-1992-1998/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-34l)
2. «SYSTEM/COMPONENT TESTS - 5.7L»(/chevrolet/camaro/iv-1992-1998/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-57l)

Although several types of ignition systems are used, all ignition systems (except 5.7L Opti-Spark) use the same 4 basic ignition circuits. Models use an Opti-Spark system (5.7L) or one of 3 types of distributorless ignition systems. See IGNITION SYSTEM.

The ignition control module is connected to PCM by 4 EST circuits. Circuits perform the following functions

1. By-Pass

When an engine speed signal of approximately 400 RPM is received by the PCM, PCM considers engine to be running and applies 5 volts to the ignition control module on the by-pass wire. This causes ignition control module to switch timing control over to the variable timing control circuit in the PCM. An open or grounded by-pass circuit will set a related diagnostic trouble code in PCM memory. The engine will run at base timing plus a small amount of advance.

1. EST

When 5 volts is present on the by-pass circuit and ignition control module has turned control of engine timing over to PCM, the PCM advances or retards spark on this circuit based on calculations involving the reference signal and other sensor input signals. If base timing is incorrectly set, entire advance curve will be incorrect.

1. Ground

This is the reference ground circuit. It is grounded at distributor and PCM, ensuring no voltage drop occurs in the EST circuit which could affect ignition operation.

1. Reference (RPM)

Alternating current signals from the pick-up coil (HEI distributor), PM generator (DIS and IDI) are converted by the ignition control module converter to digital signals for use by PCM. This supplies RPM data and crankshaft position reference to PCM. Because signal on this circuit is used as an injector trigger reference, engine will not run if circuit is open or grounded.

In conjunction with the ignition system, a knock sensor retard system is used. System consists of a knock sensor, knock sensor module (if equipped) and PCM. When detonation (engine knock) occurs, knock sensor produces a low voltage AC signal. This signal inputs to the PROM or knock sensor module (if equipped) located internal of PCM.

PCM supplies a 5-volt DC reference signal on the knock sensor signal line. Internal circuitry of the knock sensor will pull this voltage down to about 2.5 volts. When detonation (engine knock) occurs, the knock sensor produces an AC voltage signal which rides on the 2.5-volt DC signal back to the knock sensor module or PCM. The voltage and frequency of this signal depend upon knock signals received by the knock sensor. The PCM will retard ignition control timing until signals from knock sensor cease.

Failure in knock sensor circuit should set a related diagnostic trouble code. If a related diagnostic trouble code is not present and the knock sensor system is suspected as the cause of a driveability problem, perform a functional check of the knock sensor. See appropriate I - SYSTEM & COMPONENT TESTING article in the ENGINE PERFORMANCE section below.

1. «SYSTEM/COMPONENT TESTS - 3.4L»(/chevrolet/camaro/iv-1992-1998/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-34l)
2. «SYSTEM/COMPONENT TESTS - 5.7L»(/chevrolet/camaro/iv-1992-1998/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-57l)

EMISSION SYSTEMS

Note. To determine emission systems usage, see appropriate EMISSION APPLICATIONS article.

Air injection system helps reduce hydrocarbon (HC), carbon monoxide (CO) and oxides of nitrogen (NOx) exhaust emissions by injecting air into the exhaust system. The induction of additional air promotes further oxidation (combustion) of unburned and partially burned exhaust gases. During cold engine operation, air is injected into exhaust manifold. This quickly warms up catalytic converter and oxygen sensor. When vehicle warms up, air is diverted to atmosphere or to the catalytic converter. See CATALYTIC CONVERTER.

Air Pump (Electric)

Air pump is a sealed, non-serviceable, electric-motor type. Pump is energized by an PCM-controlled air pump relay, which is activated when fuel system is functioning in "open loop" mode and/or less than a predetermined amount of time has passed since relay was energized. See ELECTRIC AIR PUMP RELAY.

Check Valve

The check valve prevents the backflow of exhaust gases into the air injection system. The check valve closes when exhaust gas pressure in exhaust manifold exceeds pressure delivered by pump. This occurs when air pump by-passes at high speeds, air delivery is switched to catalytic converter, air is diverted to atmosphere or air cleaner, or air pump malfunctions.

Electric Air Pump Relay

When vehicle is cold ("open loop" mode), PCM provides a ground for the electric air pump relay. When relay is energized, power is supplied to the electric air pump. When fuel system goes into "closed loop" or electric air pump has been on for more than a precalibrated period, the PCM opens the ground circuit. When relay is de-energized on, air is diverted to the atmosphere until air pump stops spinning, or an internal stop valve closes when relay is de-energized.

CATALYTIC CONVERTER

A 3-way catalytic (TWC) converter is used on all vehicles to reduce exhaust emissions. This type of converter reduces hydrocarbon (HC), carbon monoxide (CO) and oxides of nitrogen (NOx) levels.

TWC

Converter contains a reducing agent (Rhodium and Platinum) to reduce NOx and an oxidizing agent (Palladium and Platinum) to oxidize HC and CO. This causes HC and CO to oxidize (break down with the addition of oxygen and heat) into the harmless base elements: water (H2O) and carbon dioxide (CO2). Oxygen is removed from NOx, causing it to reduce to the harmless base elements nitrogen (N) and oxygen (O2).

EXHAUST GAS RECIRCULATION (EGR)

The Exhaust Gas Recirculation (EGR) system is designed to reduce oxides of nitrogen (NOx) emissions by lowering combustion temperatures. This is accomplished when a metered amount of exhaust gas is recirculated into the intake manifold and mixed with the air/fuel mixture.

The 2 types of EGR systems used are pulse width modulated negative backpressure EGR using an EGR solenoid and either ported or manifold vacuum, and digital or linear EGR.

On PCM-controlled EGR systems using a solenoid, PCM controls ported or manifold vacuum to EGR valve through solenoid valve. Solenoid may be normally open or normally closed, depending upon application.

PCM uses engine coolant temperature, throttle position and manifold pressure signals to determine vacuum solenoid operation. During cold engine operation and idle, EGR is not desired; PCM causes solenoid to block vacuum to EGR valve. During warm engine operation and at speeds greater than idle, vacuum is allowed through solenoid, opening EGR valve. To check EGR system, perform functional check of EGR system. See appropriate I - SYSTEM & COMPONENT TESTING article in the ENGINE PERFORMANCE section below.

1. «SYSTEM/COMPONENT TESTS - 3.4L»(/chevrolet/camaro/iv-1992-1998/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-34l)
2. «SYSTEM/COMPONENT TESTS - 5.7L»(/chevrolet/camaro/iv-1992-1998/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-57l)

Digital EGR System

The digital EGR valve is designed to accurately supply EGR to engine, independent of intake manifold vacuum. The valve controls EGR flow from exhaust to intake manifold through 3 internally-mounted solenoids. When each solenoid is energized, a pintle is lifted to allow exhaust gas to flow through valve. Solenoids are energized individually, in pairs or together to provide 7 different EGR flow ratios. This enables PCM to tailor EGR flow to specific engine requirements.

Linear EGR System

The linear EGR valve is designed to accurately supply EGR to engine, independent of intake manifold vacuum. The valve controls EGR flow from exhaust to intake manifold through an orifice with a PCM-controlled pintle. PCM controls pintle position by monitoring the pintle position feedback signal.

Negative Backpressure EGR Valve

EGR uses negative backpressure EGR valve. Backpressure EGR also use an PCM-controlled solenoid to regulate vacuum signal to EGR valve. Vacuum is applied to upper EGR diaphragm via a hose connected to intake manifold vacuum. Manifold vacuum is also applied to lower EGR diaphragm (through intake port at base of EGR valve). When manifold vacuum in lower chamber is insufficient to overcome spring tension on lower diaphragm, bleed valve will be closed, allowing vacuum in upper chamber to open EGR valve. With engine at idle or under light load, high manifold vacuum applied to lower chamber opens air bleed valve in lower diaphragm. This bleeds off vacuum in upper chamber, keeping the EGR valve closed.

EVAPORATIVE EMISSION CONTROL

Carbon canister storage is used for evaporative fuel control on all vehicles. The function of evaporative emission control system is to store gasoline fumes from fuel tank in a carbon canister until fumes can be drawn into engine for burning during combustion process.

Evaporative emission system uses 4 basic components

1. Activated carbon canister (may be sealed or open at top or bottom for fresh air intake).
2. Tank pressure control valve (mounted internally or externally to fuel tank).
3. PCM-controlled canister purge control solenoid (mounted in -line or on canister).
4. Canister purge control valve (mounted in-line or on canister).

For specific component application, see EMISSION APPLICATIONS article. For vacuum hose routing, see VACUUM DIAGRAMS article.

Carbon Canister

Evaporative fumes from the fuel tank are vented through hoses into a canister containing activated carbon. The activated carbon absorbs and holds fuel vapors when the engine is not operating. When the engine is started and engine speed is greater than idle (purge at idle would cause too rich a mixture), engine vacuum draws fuel vapors from the canister into the engine. Regulation of vapors through this purge line is controlled by a PCM-controlled canister purge control solenoid.

Carbon canisters are either open or closed design. When the engine is started on open canister models, engine vacuum draws outside air into canister either through the top or through a filter in bottom of canister. This helps to purge vapors from the activated carbon.

Note. Models without fuel tank pressure control valves may use a special pressure/vacuum relief fuel tank filler cap or other external relief device.

Canister purge control solenoid is controlled by the PCM. Current is supplied to solenoid when the ignition is on. Solenoid is energized when PCM provides a ground circuit for solenoid. Solenoid may be normally closed or normally open. When solenoid is open, charcoal canister is purged using manifold or ported vacuum. When solenoid is closed, purge vacuum to canister is blocked.

The PCM will allow vacuum to pass through solenoid when engine has been running for more than one minute, coolant temperature is greater than 176°F (80°C), vehicle speed is greater than 5 MPH and throttle is off idle. This solenoid (if used) is located in the purge line between charcoal canister and vacuum purge port, or on top of canister.

Canister Purge Control Valve

Canister purge control valve is a vacuum regulated/purge control valve located in vapor delivery hose between fuel tank and carbon canister, or on top of canister. When engine is not running and tank pressure is less than .7 psi (.49 kg/cm 2 ), internal spring pressure holds valve in the closed position.

This causes fuel tank low-pressure vapors to be vented through a restriction in valve. This restriction will retain most fuel tank vapors in fuel tank. When tank pressure rises and overrides spring tension, fumes are vented to the carbon canister. When engine is running, vacuum is applied to upper port of valve, opening passage between fuel tank and carbon canister, which is purged by engine vacuum.

Tank Pressure Control Valve

Tank pressure control valve is a vacuum regulated/pressure control valve located in fuel tank or in vapor delivery hose between fuel tank and carbon canister. When engine is not running and tank pressure is less than .9 psi (.63 kg/cm 2 ), internal spring pressure holds valve in the closed position.

This causes fuel tank low-pressure vapors to be vented through a restriction in valve. This restriction will retain most fuel tank vapors in fuel tank. When tank pressure rises and overrides spring tension, fumes are vented to the carbon canister. When engine is running, vacuum is applied to upper port of valve, opening passage between fuel tank and carbon canister, which is purged by engine vacuum.

POSITIVE CRANKCASE VENTILATION (PCV)

The PCV system is used to provide more effective elimination of crankcase vapors. Fresh air from the air filter housing or throttle body is supplied to the crankcase where it is mixed with blow-by gases and passed through a PCV valve into the intake manifold. This mixture is then passed into the combustion chamber and burned.

The PCV valve provides primary control in this system by metering the flow of the blow-by vapors, according to manifold vacuum. When manifold vacuum is high (at idle), the PCV restricts the flow to maintain a smooth idle condition.

Under conditions in which abnormal amounts of blow-by gases are produced (such as worn cylinders or rings), the system is designed to allow the excess gases to flow back through crankcase vent hose into the intake or throttle body to be consumed during normal combustion.

SELF-DIAGNOSTIC SYSTEM

The PCM is equipped with a self-diagnostic system which detects system failures or abnormalities. When a malfunction occurs, PCM will illuminate the Malfunction Indicator Light (MIL) located on instrument cluster. When malfunction is detected and MIL is turned on, a corresponding diagnostic trouble code will be stored in PCM memory. Malfunctions are designated as either "hard failures" or as "intermittent failures". To retrieve stored codes, see appropriate TESTS W/CODES article in the ENGINE PERFORMANCE section below.

1. «TESTS W/CODES - 3.4L»(/chevrolet/camaro/iv-1992-1998/remont/testing-diagnostics/#engine-controls-tests-wcodes-34l)
2. «TESTS W/CODES - 5.7L»(/chevrolet/camaro/iv-1992-1998/remont/testing-diagnostics/#engine-controls-tests-wcodes-57l)

"Hard Failures"

Hard failures cause MIL to illuminate and remain on until the malfunction is repaired. On models using digital display on dash to indicate codes, codes may be accompanied by a "current" or "history" indication for intermittent and hard codes. If light comes on and remains on during vehicle operation, cause of malfunction must be determined using diagnostic trouble code charts located in appropriate TESTS W/CODES article in the ENGINE PERFORMANCE section below. If a sensor fails, PCM will use a substitute value in its calculations to continue engine operation. In this condition, vehicle is functional but loss of good driveability is likely.

1. «TESTS W/CODES - 3.4L»(/chevrolet/camaro/iv-1992-1998/remont/testing-diagnostics/#engine-controls-tests-wcodes-34l)
2. «TESTS W/CODES - 5.7L»(/chevrolet/camaro/iv-1992-1998/remont/testing-diagnostics/#engine-controls-tests-wcodes-57l)

"Intermittent Failures"

Intermittent failures cause MIL to flicker or glow and go out about 10 seconds after the intermittent fault goes away. The corresponding diagnostic trouble code, however, will be retained in PCM memory. On models using digital display on dash to indicate codes, codes may be accompanied by a "current" or "history" indication for intermittent and hard codes. If related fault does not reoccur within 50 engine restarts, related diagnostic trouble code will be erased from PCM memory. Intermittent failures may be caused by sensor, connector or wiring related problems. See TESTS W/O CODES - 3.4L/5.7L article in the ENGINE PERFORMANCE section.

As a bulb and system check, MIL will illuminate when ignition switch is turned to ON position and engine is not running. When engine is started, light should go out. If light does not go out, a malfunction has been detected in the computerized engine control system or MIL circuit is faulty. Light may be used on some models to display stored diagnostic trouble codes. To access codes using "scan" or "non-scan" methods, see appropriate TESTS W/CODES article in the ENGINE PERFORMANCE section below.

1. «TESTS W/CODES - 3.4L»(/chevrolet/camaro/iv-1992-1998/remont/testing-diagnostics/#engine-controls-tests-wcodes-34l)
2. «TESTS W/CODES - 5.7L»(/chevrolet/camaro/iv-1992-1998/remont/testing-diagnostics/#engine-controls-tests-wcodes-57l)

PCM is equipped with a serial data line. Serial data is a stream of electrical impulses which can be interpreted by special testers of other control modules. On some models, serial data and codes must be accessed using special "scan" testers connected to the Data Link Connector (DLC). Update intervals and information contained within the data stream vary with model application.

On some models, serial data may be accessed using the Driver Information Center (DIC) and Climate Control Panel (CCP). On these models, serial data may be shared with A/C controller, supplemental restraint controller, anti-lock brake controller and even cruise control unit.

MISCELLANEOUS CONTROLS

Note. Although not considered true engine performance-related systems, some controlled devices may affect driveability if they malfunction.

On many models, PCM regulates operation of the A/C compressor clutch through a PCM-controlled A/C compressor clutch relay. This allows the PCM to disengage the A/C compressor when compressor load on engine may cause driveability problems (i.e., during hot restart, idle, low speed steering maneuvers and wide open throttle operation), or if A/C refrigerant pressure drops below or rises above normal operating levels.

Refrigerant pressure sensing may be accomplished by monitoring high and low pressure switches or a pressure sensor which will register either high or low pressure levels. Power steering load is monitored through a power steering pressure switch. Hot restart is monitored through the coolant temperature sensor. For component application and related wiring, see A/C wiring schematics under MISCELLANEOUS CONTROLS in appropriate I - SYSTEM & COMPONENT TESTING article in the ENGINE PERFORMANCE section below.

1. «SYSTEM/COMPONENT TESTS - 3.4L»(/chevrolet/camaro/iv-1992-1998/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-34l)
2. «SYSTEM/COMPONENT TESTS - 5.7L»(/chevrolet/camaro/iv-1992-1998/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-57l)

Some models are equipped with an air conditioner pressure sensor which is used to inform PCM of A/C system pressure levels. Low pressure signal will cause A/C compressor to disengage to prevent system damage. High pressure levels cause PCM to engage high speed fans while A/C compressor clutch is engaged. Extremely high pressure levels will cause PCM to disengage A/C compressor clutch to prevent system damage.

A/C high and low pressure switches may be used in the PCM-monitored A/C request circuit. Switches are normally closed, completing the circuit between ignition and PCM. PCM will engage or disengage A/C compressor clutch relay based upon status of this circuit. When system refrigerant pressure increases beyond a certain point, high side switch will open, causing A/C request circuit voltage to drop.

If system refrigerant level decreases, causing refrigerant pressure to drop below normal, low side pressure switch will open, causing A/C request circuit voltage to drop. Switches may be used as normal clutch cycling devices or as safety devices which prevent compressor damage in the event of excessively high or low refrigerant pressure.

ELECTRIC COOLING FAN

On many models, PCM regulates operation of electric cooling fan through a PCM-controlled cooling fan relay which controls the ground circuit or power circuit for the cooling fan. This allows PCM to operate cooling fan based upon engine coolant temperature. Most systems will engage electric cooling fan whenever A/C clutch is engaged, regardless of engine temperature. A malfunction of the cooling fan will cause engine overheating and possible detonation.

Some models use more than one cooling fan. The second fan may function as an auxiliary cooling device when A/C is engaged or (on models using A/C high and low pressure switches) during periods of engine overheating, or high A/C refrigerant pressures.

For component application and related wiring, see wiring schematics under MISCELLANEOUS CONTROLS in appropriate I - SYSTEM & COMPONENT TESTING article in the ENGINE PERFORMANCE section below.

1. «SYSTEM/COMPONENT TESTS - 3.4L»(/chevrolet/camaro/iv-1992-1998/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-34l)
2. «SYSTEM/COMPONENT TESTS - 5.7L»(/chevrolet/camaro/iv-1992-1998/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-57l)

HOT LIGHT OR COOLANT TEMPERATURE LIGHT

When engine coolant temperature sensor input indicates temperature exceeds specified range, PCM will turn on the TEMP or HOT light by providing a ground for the light circuit. As a bulb check, PCM also supplies a ground to turn on light when ignition is first turned on.

Torque Converter Clutch (Non-Electronic Transmission)

The purpose of the transmission/transaxle converter clutch feature is to eliminate power loss of torque converter stage when vehicle is in a cruise condition. This allows convenience of automatic transmission/transaxle and fuel economy of a manual transmission.

Fused battery ignition is supplied to TCC solenoid through a brake switch. On some models, gear hydraulic apply switches (located within the transmission) may also be in series with solenoid power or ground circuit. For wiring reference, see wiring schematics under MISCELLANEOUS CONTROLS in appropriate I - SYSTEM & COMPONENT TESTING article in the ENGINE PERFORMANCE section below.

1. «SYSTEM/COMPONENT TESTS - 3.4L»(/chevrolet/camaro/iv-1992-1998/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-34l)
2. «SYSTEM/COMPONENT TESTS - 5.7L»(/chevrolet/camaro/iv-1992-1998/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-57l)

Converter clutch will engage when vehicle is moving faster than a precalibrated speed, engine is at normal operating temperature, throttle position sensor output is not changing (indicating a steady vehicle speed), transmission 3rd gear switch is closed (if equipped), and brake switch is closed.

When vehicle speed is great enough (about 20-45 MPH as indicated by the vehicle speed sensor), PCM energizes TCC solenoid mounted in transmission. This allows torque converter to directly connect engine to the transmission. When operating conditions indicate transmission should operate as normal, TCC solenoid is de-energized.

This allows transmission to return to normal automatic operation. Since power for the TCC solenoid is delivered through the brake switch, transmission will also return to normal automatic operation when brake pedal is depressed. To check TCC system, perform functional check of TCC system. See MISCELLANEOUS CONTROLS in appropriate I - SYSTEM & COMPONENT TESTING article in the ENGINE PERFORMANCE section below.

1. «SYSTEM/COMPONENT TESTS - 3.4L»(/chevrolet/camaro/iv-1992-1998/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-34l)
2. «SYSTEM/COMPONENT TESTS - 5.7L»(/chevrolet/camaro/iv-1992-1998/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-57l)

Torque Converter Clutch (Electronic Transmission)

The torque converter clutch functions similarly to the non-electronic type except instead of a single internal TCC solenoid, 2 solenoids are used. A standard TCC solenoid is used in conjunction with a Pulse Width Modulated (PWM) solenoid that regulates hydraulic pressure to make locking and unlocking of the TCC smoother.

Electronic Transmission

On vehicles equipped with electronic transmission, transmission is controlled by the Powertrain Control Module (PCM). PCM controls other vehicle functions as well as the transmission. The PCM monitors a number of engine/vehicle functions and uses the data to control shift solenoid "A", shift solenoid "B", TCC and, on some models, transaxle pressure control solenoid to regulate TCC engagement, upshift pattern, downshift pattern and line pressure (shift quality).

1. Shift Solenoid "A"

Shift solenoid "A" is attached to the valve body and is a normally open exhaust valve. PCM activates solenoid by grounding it through an internal quad-driver. Solenoid "A" is on in 1st and 4th gears but off in 2nd and 3rd gears. When on, solenoid redirects fluid to act on the shift valves.

1. Shift Solenoid "B"

Shift solenoid "B" is attached to the valve body and is a normally open exhaust valve. PCM activates solenoid by grounding it through an internal quad-driver. Solenoid "B" is on in 3rd and 4th gears but off in 1st and 2nd gears. When on, solenoid redirects fluid to act on the shift valves.

1. Transaxle Pressure Control Solenoid

Transaxle pressure control solenoid is attached to the valve body and controls line pressure by moving a pressure regulator valve against spring pressure. Transaxle pressure control solenoid takes the place of the force motor used on past model transmissions. PCM varies line pressure based upon engine load. Engine load is calculated from various inputs, especially the TP sensor.

Line pressure is actually varied by changing the amperage applied to the transaxle pressure control solenoid from zero (high pressure) to 1.1 amps (low pressure). The transaxle pressure control solenoid is periodically pulsed to prevent the pressure regulator valve from sticking due to fluid contamination.

The shift light is used on M/T models. Light indicates the best transmission shift point for maximum fuel economy based on engine speed and load. Power for light is supplied through the GAUGES fuse. Light illuminates when PCM supplies a ground circuit for bulb. For wiring reference, see MISCELLANEOUS CONTROLS in appropriate I - SYSTEM & COMPONENT TESTING article in the ENGINE PERFORMANCE section.

1. «SYSTEM/COMPONENT TESTS - 3.4L»(/chevrolet/camaro/iv-1992-1998/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-34l)
2. «SYSTEM/COMPONENT TESTS - 5.7L»(/chevrolet/camaro/iv-1992-1998/remont/testing-diagnostics/#engine-controls-systemcomponent-tests-57l)

3.4L (VIN S) PCM Wiring Diagram (1 Of 3). Scheme 1

3.4L (VIN S) PCM Wiring Diagram (2 Of 3). Scheme 2

3.4L (VIN S) PCM Wiring Diagram (3 Of 3). Scheme 3

5.7L (VIN P) PCM Wiring Diagram (1 Of 3). Scheme 4

5.7L (VIN P) PCM Wiring Diagram (2 Of 3). Scheme 5

5.7L (VIN P) PCM Wiring Diagram (3 Of 3). Scheme 6

See also:
• TESTS W/CODES - 3.4L
• TESTS W/CODES - 5.7L
• SYSTEM/COMPONENT TESTS - 3.4L
• SYSTEM/COMPONENT TESTS - 5.7L
• SPECIFICATIONS
• BASIC TESTING - 3.4L/5.7L
• TESTS W/O CODES - 3.4L/5.7L