The following terms and acronyms are used throughout this book and course.
Accelerator Pedal Positon (APP) Sensors — three potentiometers housed in a module at the accelerator pedal, they transmit accelerator pedal position to the PCM. Resistance for the sensors is ramped at three different rates to provide fail-safe protection.
Baro Sensor — see “EGR Control Pressure/Baro Sensor”
Boost Sensor — a sensor mounted on top of the upper intake, it measures changes in intake manifold pressure. The boost sensor reads engine load and speed changes, then converts the change in readings to voltage output.
Buffer Module, VSS — see “VSS Buffer Module”
Catalytic Converter — a device that helps reduce the level of undesirable exhaust particulates.
The catalytic converter used on the 6.5L EFI diesel is a palladium-oxidation type. Unlike gasoline converters, this diesel converter does not “light off.”
Cam Signal, Pump — a reference signal emitted by the 8 slots on the disk located in the injection pump. These signals are used by the PCM to calculate injection timing. The pump cam signal is one of the most important inputs to the PCM on the 6.5L EFI diesel.
Control Valve — a spool-type plunger located at the front of the injection pump rotor. The valve controls fill/spill modes. At the beginning of the injection cycle (fill), the valve allows fuel to enter the rotor. During pressuzation and metering, the valve remains closed. At the end of the cycle (spill), the valve opens to allow fuel out of the rotor.
Crankshaft Position Sensor — a Hall-effect device that reads the rotational speed of the crank shaft sprocket. The sensor transmits this information as a digital signal to the PCM. The PCM uses the data to detemine engine speed in RPMs.
Cruise Control — a set of three switches housed in the steering column/multifunction turn signal indicator. The switches transmit information regarding cruise control ON/OFF, set/coast, and resume/accelerate status. The PCM uses this information to adjust fuel control in order to maintain vehicle speed.
Diagnostic Link Connector (DLC) — a 12-pin terminal located under the instrument panel. The DLC is used in the assembly plant to determine proper vehicle operation before it leaves the plant. The DLC is also used in service to access Diagnostic Trouble Codes (DTCs), either manually or with a “Scan” tool.
Diagnostic Trouble Codes (DTCs) — diagnostic numbers obtained at the Diagnostic Link Connector (DLC) that identify specific system malfunctions. DTCs can be obtained manually by jumping DLC terminal “B” to “A” to by using the Tech 1 “Scan” tool. A complete list of DTCs is found on the following pages.
EGR Control Pressure/Baro Sensor — a sensor used to monitor the amount of vacuum in the EGR circuit. On vehicles not equipped with EGR, this sensor is used to monitor barometric pressure. The sensor is located on the driver’s side of the cowl.
EGR Solenoid — an electrical device that opens and closes the EGR valve. The solenoid is controlled by the PCM, which determines when and what quantity of exhaust gas to recirculate into the intake system.
EGR Valve — a valve located on top of the intake manifold the allows exhaust gases to be recirculated into the intake system as a way to reduce engine emissions.
Engine Coolant Temperature (ECT) Sensor — a thermistor that translates engine coolant temperature into an electrical signal. At high coolant temperature, sensor resistance is low; at low coolant temperature, sensor resistance is high. The sensor signal is sent to the PCM, which uses it for fuel control and glow plug operation.
Engine Shutoff (ESO) Solenoid — a plunger-type electrical device that prevents fuel from entering the injection pump. The solenoid is normallly off (or closed). When commanded by the PCM, it turns on (opens) to allow fuel into the pump passages.
Fuel Solenoid — an electrical device in the injection pump that applies and releases the control valve. When it is “OFF,” the solenoid allows the control valve to open. When it is “ON,” the solenoid closes the control valve.
Fuel Solenoid Driver — a solid-state device located on the side of the injection pump that turns the injection solenoid “ON” and “OFF.” The driver is controlled by the PCM.
Fuel Temperature Sensor — a thermistor that converts fuel temperature into electrical signals used by the PCM. The fuel temperature sensor is located in the same assembly as the optical sensor.
Glow Plugs System— a series of 6-volt heaters used to aid starting. The glow plugs come “ON” for a specified time when the ignition is “ON.” There are two banks of glow plugs: three on the right side, three on the left side. The plugs are operated by the glow plug relay. The PCM turns the relay “ON” and “OFF” for glow plug operation. A lamp in the instrument panel alerts the driver to glow plug operation.
High Resolution Signal — see “Optical Sensor”
Injection Pump — a high pressure rotary type pump that is controlled by the PCM and meters, pressurizes, and distributes fuel to the eight injector nozzles. The 6.5L EFI diesel engine features a Stanadyne model DS pump.
Injection Timing — the procedure by which the PCM controls when and how much fuel is delivered to the injection pump, based on pump position, engine top dead center, and TDC Offset. The injection timing procedure on the 6.5L EFI diesel involves checking for DTC 88, “TDC Offset Error,” and performing the recommended procedures.
Injection Timing Stepper Motor — a two-coil motor used to advance and retard injection pump timing. The motor is connected to the advance piston, which, in turn, is connected to the pump cam ring. When the motor arm retracts, it advances timing: when the arm extends, it retards timing.
Intake Air Temperature (IAT) Sensor — a thermistor that measures the temperature of air entering the intake system and transmits it as an electrical signal to the PCM. The sensor is located on top of the intake manifold.
Lift Pump — a pump that moves fuel under low pressure from the fuel tank to the transfer pump.
Malfunction Indicator Lamp (MIL) — a lamp in the instrument panel that alerts the driver to code based system malfunction. Under most code conditions, the “Service Engine Soon” lamp will illuminate. During manual code reading, the lamp will flash codes in order from highest to lowest.
Offset, TDC — see “TDC Offset”
On-Board Diagnostic (OBD) System Check — an organized approach to identifying a vehicle problem that could be caused by a control module malfunction. The OBD System Check involves verifying proper PCM/MIL operation before proceding to further diagnosis.
Optical Sensor — a sensor that transmits injection pump speed information to the PCM. The sensor is mounted to the pump cam ring. It reads notches from a rotating disc and sends two signals to the PCM: a high resolution signal and a pump cam signal. These signals are used by the PCM to control fuel delivery and to determine pump position.
Powertrain Control Module (PCM) — a microprocessor-based control module that uses information from vehicle sensors (inputs) to control solenoids, relays, and other devices (outputs) responsible for vehicle operation. The PCM also performs system self diagnosis and has the ability to store Diagnostic Trouble Codes (DTCs) that aid in vehicle diagnosis.
Pump Cam Signal — see “Optical Sensor”
Pumping Plungers — four metal cylinders located in the injection pump cam ring. The plungers move in and out to pressurize fuel for delivery to the discharge ports.
“Scan” Tool — a bi-directional electronic tool that is used to diagnose system faults. When connected to the Diagnostic Link Connector (DLC), the “scan” tool can read Diagnostic Trouble Codes (DTCs). It can also control outputs to test their operation. The “scan” tool also has the ability to store information on a test drive for later viewing. The Tech 1 is a type of scan tool and is recommended for diagnosing General Motors vehicles.
“Service Throttle Soon” Lamp — an indicator lamp located in the instrument panel. It alerts the driver the malfunctions in the Accelerator Pedal Position (APP) sensor circuits.
Stepper Motor — see “Injection Timing Stepper Motor”
Tech 1 — see ‘“ Scan Tool”
Vehicle Speed Sensor (VSS) — an electro-magnetic device attached to the output shaft housing.
As the shaft rotates, its teeth pass the sensor, interrupting the sensor’s magnetic field. This is sent as a signal to the PCM.
VSS Buffer Module — an electronic device that processes information from the vehicle speed sensor (VSS) and outputs it in various signals to the PCM and other components. The module is matched to the vehicle’s transmission, final drive ratio, and tire size. The module is located in the instrument panel, near the PCM.
