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.
| Former Name Or Acronym | New Name Or Acronym |
|---|---|
| ALDL | Data Link Connector (DLC) |
| CHECK ENGINE Light | Malfunction Indicator Light (MIL) |
| CTS | Engine Coolant Temperature (ECT) Sensor |
| Diagnostic Circuit Check | On-Board Diagnostic (OBD) System Check |
| Engine Control Module (ECM) | (1) Powertrain Control Module (PCM) |
| ESC System | Knock Sensor (KS) System |
| EST System | Ignition Control (IC) System |
| MAT Sensor | Intake Air Temperature (IAT) Sensor |
| Park/Neutral (P/N) Switch | Park/Neutral Position (PNP) Switch |
| Port Fuel Injection | Multi Port Fuel Injection |
| Scan Data | Scan Tester (ST) Data |
| SERVICE ENGINE SOON Light | Malfunction Indicator Light (MIL) |
| Thermostatic Air Cleaner (TAC) | Air Cleaner (ACL) |
| Throttle Position Sensor (TPS) | Throttle Position (TP) Sensor |
| Throttle Position Switch | Closed Throttle Position (CTP) Switch |
| Throttle Position Switch | Wide Open Throttle (WOT) Switch |
| Viscous Converter Clutch (VCC) | Torque Converter Clutch (TCC) |
| (1) Some vehicles use a Vehicle Control Module (VCM). Either VCM or PCM may be used in this article to describe engine control module. | |
| (1) | Some vehicles use a Vehicle Control Module (VCM). Either VCM or PCM may be used in this article to describe engine control module. |
SAE TERMINOLOGY
TURBOCHARGER
The turbocharger is basically an air compressor or air pump. Its major parts include a turbine wheel, shaft, compressor wheel, turbine housing, compressor housing and center housing. The center housing contains a turbine seal, compressor seal and bearings.
The internal combustion engine is an air-breathing machine. The amount of power produced by the engine is determined not by the amount of fuel it uses, but by the amount of air it breathes in a certain period of time. Air must mix with fuel to complete the combustion cycle. When the air/fuel ratio reaches a certain point, additional fuel produces only Black smoke, not more power; the denser the smoke, the more the engine is being overfueled.
The turbocharger increases the quantity and density of air in the engine combustion chambers. The increased volume of air allows more fuel to be used while maintaining the proper air/fuel ratio. The increased air and fuel allows the engine to produce more horsepower than a non-turbocharged engine.
The turbocharger uses the normally wasted energy in the engine exhaust gas. As load on the engine is increased and the throttle is opened wider, more air/fuel mixture flows into the combustion chambers. The increased flow is burned and produces a larger volume of exhaust gas. The gas enters the exhaust manifolds, flows through the turbocharger turbine housing and turns the turbine wheel and shaft. The shaft is coupled to the compressor wheel. The compressor wheel compresses the air it receives and sends it to the intake manifold. The higher pressure in the intake manifold allows a denser charge to enter the combustion chambers.
Intake manifold pressure, or "boost", is controlled by an exhaust by-pass valve, or wastegate. The wastegate is operated by a spring-loaded diaphragm-type actuator which responds to boost pressure. The actuator, which is controlled by the wastegate solenoid, opens the wastegate to allow exhaust gases to by-pass the turbine wheel, thereby maintaining the correct boost level. The wastegate solenoid is controlled by the PCM through a turbo boost relay.
| CAUTION | On a turbocharged engine, any modification to the air intake or exhaust system which upsets the air flow balance may result in serious damage to the engine. |
The rotating assembly in the turbocharger can reach speeds of 140,000 RPM. An adequate supply of clean engine oil is essential for cooling and lubrication. Whenever a basic engine bearing has been damaged or the turbocharger is replaced, the oil and oil filter should be changed and the turbocharger flushed with clean engine oil.
| CAUTION | Loss of pressure or contamination of the oil supply to the turbocharger bearings can result in major turbocharger damage. |
Speed Density
All 6.5L engines are equipped with a MAP sensor, and use the speed density method to compute the airflow rate. Control module uses manifold pressure to calculate the airflow rate. The MAP sensor responds to manifold vacuum changes due to engine load and speed changes. The control module sends a voltage signal to the MAP sensor. Manifold pressure changes result in resistance changes in the MAP sensor.
By monitoring MAP sensor signal voltage, the control module determines manifold pressure. If MAP sensor fails, the control module supplies a fixed MAP value, and uses the TP sensor to control fuel.
Some models also use a Intake Air Temperature (IAT) sensor. Sensor allows control module to determine intake air temperature. Control module uses signal to delay EGR until intake air temperature reaches about 40°F (5°C). If intake air temperature becomes excessively high, control module compensates by slightly retarding timing.
COMPUTERIZED ENGINE CONTROLS
6.5L Diesel engine with or without turbocharger uses an electronic control system. The system consists of engine control module, input devices and output signals. PCM electronically controls fuel flow, fuel timing advance/retard, idle speed, EGR system operation, cruise control, Torque Converter Clutch (TCC) engagement, transmission shifts and glow plug system.
POWERTRAIN CONTROL MODULE (PCM)
Powertrain Control Module (PCM) is located in passenger compartment, behind glove box. It constantly monitors information from various sensors to control fuel flow, injector timing, cruise control, transmission shifts, throttle, EGR, TCC, cold advance and glow plug systems. PCM processes input signals from sensors and then sends necessary electrical responses to control these systems.
The PCM performs the diagnostic function of the system. It can recognize operational problems, alert driver through the SERVICE THROTTLE SOON light and store codes which identify problem areas to technicians making system repairs.
Memories
PCM uses 3 types of memory
- Read Only Memory (ROM) ROM is programmed information which only control module can read. The ROM program cannot be changed. If battery voltage is removed, ROM information is retained.
- 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, all information stored in RAM is lost.
- Programmable Read Only Memory (PROM) PROM is factory programmed engine calibration data which "tailors" control module for specific transmission, engine, emission, vehicle weight and rear axle ratio application. The PROM can be removed from control module. If battery voltage is removed, PROM information is retained.
INPUT DEVICES
Each sensor or switch furnishes electronic (voltage) signals to control module. The control module uses these input signals to control fuel flow, injector timing, cruise control, transmission shifts, EGR, TCC, cold advance and glow plug systems. Various models are equipped with different combinations of input devices. Not all devices are used on all models. To determine the input usage on a specific model, see appropriate wiring diagram in WIRING DIAGRAMS section at the end of this article. The available input signals include
Accelerator Pedal Position (APP) Sensor
APP sensor, mounted on accelerator pedal, contains 3 separate variable resistor circuits that monitors throttle opening angle for control module. Each APP circuit, connected to a 5-volt reference signal, has a high resistance value when throttle is closed. At wide open throttle, sensor resistance value is low and output to control module will be about 5 volts.
Barometric Absolute Pressure (BARO) Sensor
BARO is part of MAP sensor, mounted on left side of cowl, and monitors atmospheric pressure during ignition key on, engine off. The signal is converted into an altitude value by the control module. Control module uses this information to adjust fuel flow, injector timing and transmission shifts.
Boost Sensor
Boost sensor, used on turbo engines, monitors boost pressure and is used by control module to open wastegate which limits pressure. At full load under WOT, boost sensor indicate high pressure (high voltage). At closed throttle under deceleration, boost sensor will indicate low pressure (low voltage).
Coolant Temperature Sensor (CTS)
CTS is a thermistor (temperature sensitive resistor). A coolant temperature of -40°F (-40°C) produces a high resistance (100,000 ohms), while a coolant temperature of 266°F (130°C) produces a low resistance (70 ohms).
Control module supplies a 5-volt reference signal through an internal resistor to CTS and measures return voltage. Voltage is high when coolant temperature is low, and low when coolant temperature is hot. By measuring voltage, control module knows engine coolant temperature. Engine coolant temperature affects injector timing, cold advance, EGR, glow plug system, transmission shifts and TCC.
Crankshaft Position Sensor
Sensor is a PM type sensor and is mounted at front of crankshaft. Front crankshaft hub includes a wheel with 4 slots. Control module uses crankshaft position sensor to detect engine RPM. This signal is used to improve idle. If pump cam signal is lost, control module will use crankshaft position signal data to control injection timing and fuel flow.
Fuel Temperature Sensor
Sensor is part of pump cam signal sensor and works like IAT sensor. Control module uses this signal to adjust fuel delivery.
Intake Air Temperature (IAT) Sensor
IAT sensor is a thermistor (temperature sensitive resistor). Air temperature of -40°F (-40°C) produces a high resistance (100,000 ohms), while air temperature of 266°F (130°C) produces a low resistance (70 ohms).
Control module supplies a 5-volt reference signal through an internal resistor to IAT sensor and measures return voltage. Voltage is high when temperature is low, and low when temperature is hot. Engine air temperature affects fuel delivery and injector timing.
Manifold Absolute Pressure (MAP) Sensor
MAP sensor, mounted on left side of cowl, monitors vacuum in the EGR system. It senses the actual vacuum in the EGR vacuum line and sends a signal to the control module.
The signal is compared to the EGR duty cycle calculated by the control module. If there is a minor difference in the vacuum value sensed and the control module command, the control module corrects. When a major difference is sensed, the control module recognizes a fault and sends a full EGR signal.
Pump Cam Signal
The pump cam signal is an optical sensor and is mounted on the fuel injection pump. The sensor receives a 5-volt reference signal and allows the control module to measure fuel injector pulse ring RPM and position. This signal is critical to accurate fuel injection timing and start of injection.
Transmission Fluid Temperature (TFT) Sensor
TFT sensor is a thermistor (temperature sensitive resistor). Control module supplies a 5-volt reference signal through an internal resistor to sensor and measures return voltage. Monitored voltage is high when temperature is low (high sensor resistance), and low when temperature is hot.
Vehicle Speed Sensor (VSS)
Mounted on the transmission, VSS sends a pulsing signal to control module for vehicle speed calculation. This calculation is used to control transmission shifts and TCC engagement.
OUTPUT SIGNALS
Note. PCM regulates output signals to maintain correct driveability and exhaust emissions. For theory and operation of components, refer to indicated system.
Glow Plug Relay
See FUEL CONTROL under FUEL SYSTEM.
Cruise Control Solenoids
Exhaust Gas Recirculation System
See EMISSION SYSTEMS .
Fuel Injector Solenoid
See FUEL CONTROL under FUEL SYSTEM.
Injector Timing Stepper Motor
See FUEL CONTROL under FUEL SYSTEM.
Torque Converter Clutch
Transmission Shift Light (Manual Transmission)
Turbo Boost Relay (6.5L Turbo)
See TURBOCHARGER under AIR INDUCTION SYSTEM.
Wastegate Solenoid (6.5L Turbo)
See TURBOCHARGER under AIR INDUCTION SYSTEM.
FUEL DELIVERY
Pickup vehicles use an electric pump mounted on the left frame rail. Van models use a mechanical pump mounted on right side of engine. Pump pulls fuel from the fuel tank through a primary filter. The fuel is then pumped through a secondary filter, mounted on firewall (Pickups) or rear of air cleaner (Vans), and to the injection pump.
The diesel engine uses a mechanical, high pressure rotary diesel injection pump, which is gear-driven by camshaft at camshaft speed. Pump injects a precisely metered amount of fuel to each cylinder based on inputs from the PCM at the proper time.
High pressure fuel lines carry the fuel to an injection nozzle in each cylinder. All fuel lines are the same length to ensure no variance in timing. An electric fuel solenoid controls engine RPM. As the Accelerator Pedal Position (APP) sensor is pressed down, control module operates fuel solenoid through fuel solenoid driver to allow increased fuel delivery.
Diesel Injection Pump
The high pressure diesel injection pump is mounted at top of engine, below intake manifold. The pump is gear-driven by camshaft. Pump precisely governs time and amount of fuel injection based on control module controlled fuel solenoid and injector timing stepper motor.
Electrical controls mounted on injection pump are used by the control module to control fuel flow and injector timing. These include an engine shut-off solenoid. This solenoid blocks fuel from entering charging passage. The pump cam sensor, on top of injection pump, detects RPM of the pulse ring. It also includes a fuel temperature sensor. These signals help control module control amount of fuel delivery and injector timing. An injector timing stepper motor advances or retards injector timing. Control module controls amount of fuel delivered through fuel solenoid driver which operates fuel solenoid, mounted at front of injection pump. (Scheme 20)
Fuel under regulated low pressure enters rotary fuel metering valve and into a charging passage. As pump shaft rotates, fuel is directed at high pressure through each delivery pipe to an injector.
Scheme 20
Fuel Injection Lines
Eight high pressure fuel injection lines are routed from the injection pump to an injector in each cylinder. The lines are of equal length to prevent a difference in timing between cylinders. Lines are not interchangeable and are pre-bent by the manufacturer.
Glow Plug System
The control module uses various inputs to determine when glow plug operation is required. Control module uses relay to operate the glow plugs. The glow plug relay is mounted at rear of left cylinder head.
A normally operating system works as follows: at room temperature and with ignition on and engine off, the glow plugs come on for 4-6 seconds and then go off for about 3 seconds. The glow plugs then cycle on for about 1.0 second and off for about 4.5 seconds, for a total start sequence of about 16 seconds. If the engine is cranked during or after start sequence, the glow plugs will cycle on and off for a total of 16 seconds after the ignition switch is returned from the crank position, whether engine starts or not.
Glow Plugs
Glow plugs are small 6-volt heaters, powered by 12 volts to give rapid heating. Control module operates glow plugs, which cycle on when ignition switch is turned to the RUN position (prior to starting the engine). The glow plugs remain pulsing a short time after engine starting, then automatically turn off. For diagnostic information on computer controlled system, see appropriate TESTS W/CODES - DIESEL article in this section below.
- «TESTS W/CODES - 6.5L DIESEL»(/gmc/suburban/i-1992-1999/remont/testing-diagnostics/#engine-controls-tests-wcodes-65l-diesel) (for C/K Pickup, Sierra Pickup, Suburban, Tahoe & Yukon)
- «TESTS W/CODES - 6.5L DIESEL»(ref-20089) (for "P" & "G" Series Van)
| CAUTION | Using a jumper wire on by-pass relay causes glow plug failure. |
Glow Plug After-Start
Control module provides glow plug operation after starting a cold engine. This after-start operation is initiated when ignition switch is returned to RUN from START position.
Injection Nozzles
Each of the 8 combustion chambers is equipped with an injection nozzle. The injection nozzle has a single fuel inlet fitting and 2 fuel return fittings (one on each side of fuel inlet fitting). The nozzle is threaded into the cylinder head. Injection nozzles are spring loaded and calibrated to open at a specified fuel line pressure. The combustion chamber end of the nozzle has a replaceable compression seal and carbon stop seal.
Fuel Injection Pump
Electronic signals from the Acceleration Pedal Positioner (APP) sensor, temperature sensors, pump cam sensor and crankshaft position sensor are received by the control module. Based on these signals, control module controls fuel flow through fuel solenoid and fuel solenoid driver.
Advance & Retard Control
The injector timing stepper motor is designed to advance or retard injection pump timing up to 4 degrees plus or minus. Control module activates this circuit based on signals from the pump cam sensor, crankshaft position sensor and various temperature sensors. This control is mainly used during cold engine operation and for idle speed.
Curb Idle Speed
Curb idle is controlled by control module based on signals from crankshaft RPM, pump cam sensor and various temperature sensors. NO mechanical adjustment of low idle speed is possible. For further adjustment procedures, see IDLE SPEED under IDLE SPEED & MIXTURE in ADJUSTMENTS - 6.5L DIESEL article in this section.
Fast Idle Speed
Fast idle solenoid is controlled by control module. For further adjustment information, see IDLE SPEED under IDLE SPEED & MIXTURE in ADJUSTMENTS - 6.5L DIESEL article.
EXHAUST GAS RECIRCULATION (EGR)
Note. For additional information on EGR system, see appropriate TESTS W/CODES - DIESEL article in this section below.
- «TESTS W/CODES - 6.5L DIESEL»(/gmc/suburban/i-1992-1999/remont/testing-diagnostics/#engine-controls-tests-wcodes-65l-diesel) (for C/K Pickup, Sierra Pickup, Suburban, Tahoe & Yukon)
- «TESTS W/CODES - 6.5L DIESEL»(ref-20089) (for "P" & "G" Series Van)
The Exhaust Gas Recirculation (EGR) system limits formation of oxides of nitrogen (NOx) emissions by reducing peak combustion chamber temperatures in which NOx is formed. EGR system consists of EGR valve, EGR and EGR vent solenoids, and EGR fault detection. A vacuum pump is required to provide a vacuum source to operate the EGR system.
EGR Valve
EGR valve reintroduces a small amount of exhaust gas into combustion chamber, diluting air/fuel mixture and reducing combustion chamber peak temperatures, thereby reducing NOx formation.
EGR Vent/EGR Solenoids
EGR vent/EGR solenoids are mounted at rear of engine as a single assembly. Using input from engine speed sensor and APP, control module controls EGR by controlling amount of "on" and "off" time of EGR solenoid. When EGR is not needed, control module energizes EGR vent solenoid to vent vacuum. Vacuum is used to control EGR valve opening.
EGR Fault Detection
The control module uses input from the MAP sensor to measure amount of absolute pressure in EGR vacuum line. If a minor variation between calculated EGR and actual EGR is monitored by control module, the control module corrects. If variation is too great for control module to correct, an error is detected. The control module then enters default mode and sets a related trouble code in memory.
Vacuum Pump
A vacuum pump is mounted on the 6.5L engine and provides vacuum for operating emission controls (some "C", "G" and "K" Series vehicles), cruise control and heater and A/C servos. The vacuum pump is either belt- or gear-driven.
The belt-driven vacuum pump is bracket mounted to the right front of the engine. Except for the pulley, the vacuum pump is replaced as an assembly.
The gear-driven pump is mounted at the top rear of the engine and contains a permanently-mounted speed sensor. Pump is driven by a cam inside the drive assembly to which it mounts. On the lower end of the drive housing assembly is a drive gear which meshes with the camshaft gear in the engine. The drive gear causes the cam in the drive housing to rotate.
| CAUTION | The gear-driven vacuum pump (if equipped) drives the engine oil pump. DO NOT run engine with gear-driven vacuum pump removed. |
CRANKCASE DEPRESSION REGULATOR (CDR)
CDR valve, located on right valve cover, is used on all diesel engines. Valve prevents crankcase pressure from accumulating during idle by regulating (metering) crankcase pressure back into the engine. Intake manifold vacuum (only slight vacuum is present) acts against a spring-loaded diaphragm to control flow of crankcase gases. Higher intake manifold vacuum levels pull diaphragm closer to the top of the outlet tube, reducing amount of gases drawn from crankcase. As intake manifold vacuum drops, spring pressure pushes diaphragm away from top of outlet, allowing more gases to flow from crankcase into intake manifold.
Optimum pressure in crankcase is one inch of water (as measured with a manometer) at idle to 3-4 inches at full load. Too little vacuum causes oil leaks; too much vacuum pulls oil into the air crossover.
SELF-DIAGNOSTIC SYSTEM
The control module is equipped with a self-diagnostic system which detects system failures or abnormalities. When a malfunction occurs, control module illuminates the SERVICE ENGINE/THROTTLE SOON light located on instrument panel. When malfunction is detected and light is turned on, a corresponding trouble code is stored in control module memory. Malfunctions are designated as either "hard failures" or "intermittent failures". For procedures on retrieving stored codes, see appropriate TESTS W/CODES article below.
- «TESTS W/CODES - 6.5L DIESEL»(/gmc/suburban/i-1992-1999/remont/testing-diagnostics/#engine-controls-tests-wcodes-65l-diesel) (for C/K Pickup, Sierra Pickup, Suburban, Tahoe & Yukon)
- «TESTS W/CODES - 6.5L DIESEL»(ref-20089) (for "P" & "G" Series Van)
"HARD FAILURES"
Hard failures cause SERVICE ENGINE/THROTTLE SOON light to glow and remain on until malfunction is repaired. If light comes on and remains on during vehicle operation, cause of malfunction must be determined using diagnostic charts located in appropriate TESTS W/CODES article below. If a sensor fails, control module uses a substitute value in its calculations to continue engine operation. Although vehicle is functional in this condition, driveability will probably be adversely affected.
- «TESTS W/CODES - 6.5L DIESEL»(/gmc/suburban/i-1992-1999/remont/testing-diagnostics/#engine-controls-tests-wcodes-65l-diesel) (for C/K Pickup, Sierra Pickup, Suburban, Tahoe & Yukon)
- «TESTS W/CODES - 6.5L DIESEL»(ref-20089) (for "P" & "G" Series Van)
"INTERMITTENT FAILURES"
Intermittent failures cause SERVICE ENGINE/THROTTLE SOON light to flicker or illuminate and go out about 10 seconds after intermittent fault goes away. However, control module retains corresponding trouble code in memory. If related fault does not reoccur within 50 engine restarts, related trouble code is erased from control module memory. Sensor, connector or wiring related problems may cause intermittent failures. See TESTS W/O CODES - 6.5L DIESEL article in this section.
SERVICE ENGINE/THROTTLE SOON LIGHT
As a bulb and system check, SERVICE ENGINE/THROTTLE SOON light glows 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 operate as described, malfunction has been detected in computerized engine control system or SERVICE THROTTLE SOON light circuit is faulty.
To verify proper operation of SERVICE ENGINE SOON light on gasoline models, proceed to the DIAGNOSTIC CIRCUIT CHECK in the BASIC TESTING - 6.5L DIESEL article. To verify proper operation of SERVICE THROTTLE SOON light and retrieve trouble codes on diesel models, see DIAGNOSTIC SYSTEM CHECK chart under DIAGNOSTIC CHARTS in appropriate TESTS W/CODES - DIESEL article below.
- «TESTS W/CODES - 6.5L DIESEL»(/gmc/suburban/i-1992-1999/remont/testing-diagnostics/#engine-controls-tests-wcodes-65l-diesel) (for C/K Pickup, Sierra Pickup, Suburban, Tahoe & Yukon)
- «TESTS W/CODES - 6.5L DIESEL»(ref-20089) (for "P" & "G" Series Van)
SERIAL DATA
Control module has a serial data line. Serial data is a stream of electrical impulses which can be interpreted by special testers of other control modules. Access serial data by connecting special scan testers to Data Link Connector (DLC). Update intervals and information contained within data stream vary with model application.
MISCELLANEOUS PCM CONTROLS
Note. Although not considered true engine performance-related systems, some devices may affect driveability if they malfunction.
A/C CLUTCH
On many models, control module regulates operation of the A/C clutch through an control module-controlled relay. The control module disengages 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 to less than or rises to greater than normal operating levels.
Refrigerant pressure is sensed through the monitoring of high and low pressure switches or a pressure sensor which registers either high or low pressure levels. Hot restart is monitored through the coolant temperature sensor. For component application and related wiring, see wiring schematics under MISCELLANEOUS PCM CONTROLS in SYSTEM/COMPONENT TESTS - 6.5L DIESEL article.
A/C Pressure Switches
A/C high and low pressure switches may be used in the A/C compressor clutch or compressor clutch relay circuit. Switches are normally closed, completing the circuit which energizes the compressor clutch. When system freon pressure increases beyond a certain point, high side switch opens, causing compressor clutch to disengage.
If system freon level decreases (causing freon pressure to drop), low side pressure switch opens, preventing compressor damage by causing compressor clutch to disengage.
CRUISE CONTROL
On models with cruise control, the system is operated by the control module. Control module receives inputs from VSS, servo diaphragm position sensor, cruise control switch and brake release switch. Based on these inputs, control module controls vacuum valves at servo. Control module prevents system engagement at speeds of less than 25 MPH. Control module is not serviceable; if defective, it must be replaced. System faults are stored as codes in control module memory.
The transmission/transaxle converter clutch eliminates power loss of torque converter stage when vehicle is in a cruise condition, allowing driver convenience of automatic transmission and fuel economy of a manual transmission. Fused battery ignition is supplied to converter solenoid through a brake switch.
On some models, 2nd, 3rd and 4th gear hydraulic apply switches (located within transmission) may also be in series with solenoid power or ground circuit. On other models, switch status may only be monitored by control module, without sharing power or ground with converter solenoid. For wiring reference, see wiring schematics under MISCELLANEOUS PCM CONTROLS in the appropriate SYSTEM/COMPONENT TESTS - 6.5L DIESEL article.
Converter clutch engages when vehicle is moving faster than a pre-calibrated speed, engine is at normal operating temperature, throttle position sensor output is not changing (indicating a steady road speed) and transmission 3rd gear or high gear switch (if equipped) and brake switch are closed.
When vehicle speed is great enough (about 20-45 MPH as indicated by the vehicle speed sensor), control module energizes converter clutch solenoid mounted in transmission, allowing torque converter to directly connect engine to the transmission. When operating conditions indicate transmission should operate as normal, converter clutch solenoid is de-energized, allowing transmission to return to normal automatic operation. Since power for the converter solenoid is delivered through the brake switch, transmission also returns to normal automatic operation when brake pedal is depressed. To check function of converter clutch system, perform functional check of system. See MISCELLANEOUS PCM CONTROLS in the appropriate SYSTEM/COMPONENT TESTS - 6.5L DIESEL article.
Electronic Transmission (4L60-E, 4L80-E & 4T60-E)
On most vehicles, Powertrain Control Module (PCM) controls transmission and other vehicle functions. Control module monitors a number of engine/vehicle functions and uses data to control shift solenoid "A", shift solenoid "B", TCC and the force motor. Control module also regulates TCC engagement, upshift pattern, downshift pattern and line pressure (shift quality).
- Shift Solenoid "A" (1st-2nd) Shift solenoid "A" is attached to the valve body and is a normally open exhaust valve. Control module 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. When on, solenoid redirects fluid to act on the shift valves. Solenoid "A" is Blue. Code 82 is associated with solenoid "A".
- Shift Solenoid "B" (2nd-3rd) Shift solenoid "B" is attached to the valve body and is a normally open exhaust valve. Control module 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. When on, solenoid redirects fluid to act on the shift valves. Solenoid "B" is Red. Codes 81, 86 and 87 are associated with solenoid "B".
- Force Motor (Pressure Control Solenoid) Force motor is attached to valve body and controls line pressure by moving a pressure regulator valve against spring pressure. Force motor replaces throttle valve or vacuum modulator used on past transmissions. Control module varies line pressure based upon engine load. Engine load is calculated from various inputs, especially TP sensor. Line pressure is actually varied by changing amperage applied to force motor from zero (high pressure) to 1.1 amps (low pressure). Force motor is periodically pulsed to prevent fluid contamination from causing pressure regulator valve to stick.
Shift Light
Shift light may be used on vehicles equipped with manual transmission. Light indicates best transmission shift point for maximum fuel economy. Power for light is supplied through GAUGES fuse. Light illuminates when control module supplies a ground circuit for bulb. For wiring reference, see wiring schematics under MISCELLANEOUS PCM CONTROLS in SYSTEM/COMPONENT TESTS - 6.5L DIESEL article.
