Engine Control Module
ACCELERATOR PEDAL POSITION SENSOR (APPS) - ECM INPUTFig. 4 APPS Assembly Location:
Fig. 5 APPS Sensor Location (Rear View):
The APPS assembly is located at the top-left-front of the engine. A plastic cover is used to cover the assembly. The actual sensor is located behind its mounting bracket.
The Accelerator Pedal Position Sensor (APPS) is a linear potentiometer. It provides the Engine Control Module (ECM) with a DC voltage signal proportional to the angle, or position of the accelerator pedal. In previous model years, this part was known as the Throttle Position Sensor (TPS).
Diesel engines used in previous model years used a mechanical cable between the accelerator pedal and the TPS lever. Linkage and bellcranks between the TPS cable lever and the fuel injection pump were also used. Although the cable has been retained with the APPS, the linkage and bellcranks between the cable lever and the fuel injection pump are no longer used.
The APPS is serviced (replaced) as one assembly including the lever, brackets and sensor. The APPS is calibrated and permanently positioned to its mounting bracket.
CAUTION: Do not attempt to remove sensor from its mounting bracket as electronic calibration will be destroyed (sensor-to-bracket mounting screws are permanently attached). Two accelerator lever set screws are used to position lever. Do not attempt to alter positions of these set screws as electronic calibration will be destroyed.
BATTERY VOLTAGE - ECM INPUT
The battery voltage input provides power to the Engine Control Module (ECM). It also informs the ECM what voltage level is being supplied by the generator once the vehicle is running.
The battery input also provides the voltage that is needed to keep the ECM memory alive. The memory stores Diagnostic Trouble Code (DTC) messages.
CAMSHAFT POSITION SENSOR (CMP) - ECM INPUT
Fig. 6 Camshaft Position Sensor (CMP) Location:
The CMP is located below the fuel injection pump. It is attached to the back of the timing gear cover housing.
Fig. 7 Camshaft Position Sensor (CMP):
The Camshaft Position Sensor (CMP) contains a hall effect device called a sync signal generator to generate a sync signal.
The sync signal generator detects a machined hole on the rear face of the camshaft drive gear. The signal is used to verify the position of the #1 cylinder during engine operation.
When the leading edge of the machined hole enters the tip of the CMP the interruption of magnetic field causes the voltage to switch high resulting in a signal of approximately 5 volts.
When the trailing edge of the machined hole leaves the tip of the CMP, the change of the magnetic field causes the voltage to switch low to 0 volts.
The CMP is not used for any control of fuel system. It is used only for diagnostic purposes.
CCD BUS (+/-) CIRCUITS - ECM/PCM INPUTS AND OUTPUTS
The Engine Control Module (ECM) and the Powertrain Control Module (PCM) send certain signals through the CCD bus circuits. Some of these signals are parallel circuited between the two control modules (ECM and PCM). These signals are used to control certain instrument panel located items and to determine certain identification numbers.
CRANKSHAFT POSITION SENSOR (CKP) - ECM INPUT
Fig. 8 Crankshaft Position Sensor (CKP) Location:
The Crankshaft Position Sensor (CKP) is located on the lower left-rear side of the engine behind the starter motor.
Engine speed and crankshaft position are provided through the CKP. The sensor generates pulses that are the input sent to the Engine Control Module (ECM). The ECM interprets the sensor input to determine the crankshaft position. The ECM then uses this position, along with other inputs, to determine injector firing sequence and fuel timing. The sensor must be powered up by 5 volts to operate.
The sensor is a hall effect device combined with an internal magnet. It is also sensitive to steel within a certain distance from it.
Fig. 9 Crankshaft Tone Wheel:
The engine crankshaft is equipped with a bolt-on tone wheel. The tone wheel is equipped with 35 teeth and a gap where the 36th tooth should be placed. This missing tooth indicates to the ECM the relative position of cylinder #1 to the Top Dead Center (TDC) position. This does not mean that cylinder #1 is at TDC. When the CKP is aligned with the missing tooth, the missing tooth is 60 degrees away from cylinder #1 TDC position. The teeth cause pulses to be generated when they pass under the sensor. The pulses are the input to the ECM.
ENGINE COOLANT TEMPERATURE (ECT) SENSOR - ECM INPUT
Fig. 10 Engine Coolant Temperature Sensor:
The engine coolant temperature sensor is installed into the front of the cylinder head near to the thermostat housing and protrudes into a water jacket.
The ECT sensor provides an input voltage to the Engine Control Module (ECM) to monitor coolant temperature. The ECM uses this input along with inputs from other sensors for engine protection, fuel timing and fuel control. As coolant temperature varies, the coolant temperature sensor resistance will change. This change in resistance results in a different input voltage to the ECM.
FUEL TEMPERATURE SENSOR
Two different fuel temperature sensors are used. One of the sensors is located inside of the Bosch VP44 fuel injection pump and is a non-serviceable part. The other fuel temperature sensor is located in the top of the fuel filter housing and is serviceable (serviceable if replacing the fuel heater).
The sensor located in the Bosch VP44 fuel injection pump is used to check fuel temperature within the injection pump and to set a Diagnostic Trouble Code (DTC) if a specific high fuel temperature has been reached. If high temperature has been reached, engine power will be de-rated by the Engine Control Module (ECM).
The sensor located in the top of the fuel filter housing is used to control the fuel heater element. Refer to Fuel Heater Description and Operation for additional information.
INTAKE MANIFOLD AIR TEMPERATURE (IAT) SENSOR - ECM INPUT
Fig. 11 Intake Manifold Air Temperature (IAT) Sensor Location:
The intake manifold air temperature sensor is installed into the rear of the intake manifold with the sensor element extending into the air stream.
The IAT provides an input voltage to the Engine Control Module (ECM) indicating intake manifold air temperature. The input is used along with inputs from other sensors for intake air heater element operation, for engine protection, fuel timing and fuel control. As the temperature of the air-fuel stream in the manifold varies, the sensor resistance changes. This results in a different input voltage to the ECM.
MANIFOLD AIR PRESSURE (MAP) SENSOR - ECM INPUT
The MAP sensor is installed into the rear of the intake manifold.
The MAP sensor reacts to air pressure changes in the intake manifold. It provides an input voltage to the Engine Control Module (ECM). As pressure changes, MAP sensor voltage will change. The change in MAP sensor voltage results in a different input voltage to the ECM. The ECM uses this input, along with inputs from other sensors to provide fuel timing, fuel control and engine protection. Engine protection is used to derate (drop power OFF) the engine if turbocharger pressure becomes to high.
OIL PRESSURE SENSOR - ECM INPUT
Fig. 12 Engine Oil Pressure Sensor Location:
The 3-wire, solid-state oil pressure sensor is installed into the oil pressure galley on the engine block. It is located below and to the rear of the Engine Control Module (ECM).
Operation of the oil pressure sensor on the diesel engine is controlled by the Engine Control Module (ECM). The Powertrain Control Module (PCM) does not have any control over the sensor.
The oil pressure sensor uses three circuits. They are:
- A 5-volt power supply from the ECM
- A sensor ground through the ECM's sensor return
- A signal to the ECM relating to engine oil pressure
The oil pressure sensor has a 3-wire electrical function very much like the Manifold Absolute Pressure (MAP) sensor on the gasoline powered engine. Meaning different pressures relate to different output voltages.
A 5-volt supply is sent to the sensor from the ECM to power up the sensor. The sensor returns a voltage signal back to the ECM relating to engine oil pressure. This signal is then transferred (bussed) to the instrument panel on the CCD bus circuit to operate the oil pressure gauge and the check gauges lamp. Ground for the sensor is provided by the ECM through a low-noise sensor return.
PTO SWITCH SENSE - ECM INPUT
This Engine Control Module (ECM) input is used only on models equipped with aftermarket Power Take Off (PTO) units.
The input is used to tell the ECM that the PTO has been engaged. When engaged, the ECM will disable certain OBD II functions until the PTO has been turned OFF.
WATER-IN-FUEL (WIF) SENSOR - ECM INPUT
Fig. 13 Water-In-Fuel Sensor Location:
The WIF sensor is located on the side of the fuel filter/water separator canister.
The sensor sends an input to the Engine Control Module (ECM) when it senses water in the fuel filter/water separator. As the water level in the filter/separator increases, the resistance across the WIF sensor decreases. This decrease in resistance is sent as a signal to the ECM and compared to a high water standard value. Once the value reaches 30 to 40 kilo ohms, the ECM will activate the water-in-fuel warning lamp through CCD bus circuits. This all takes place when the ignition key is initially put in the ON position. The ECM continues to monitor the input at the end of the intake manifold air heater post-heat cycle.
FUEL INJECTION PUMP RELAY - ECM OUTPUT
The fuel injection pump relay is located in the Power Distribution Center (PDC). Refer to label under PDC cover for relay location.
The Engine Control Module (ECM) energizes the electric fuel injection pump through the fuel injection pump relay. Battery voltage is applied to the fuel injection pump relay at all times. When the key is turned ON, the relay is energized when a 12-volt signal is provided by the ECM. When energized, 12-volts is supplied to the Fuel Pump Control Module. The Fuel Pump Control Module is located on the top of the fuel injection pump and is non-servicable.
INTAKE MANIFOLD AIR HEATER ELEMENTS
Fig. 14 Air Heater Elements Location:
The intake manifold air heater element assembly is located in the top of the intake manifold.
The air heater elements are used to heat incoming air to the intake manifold. This is done to help engine starting and improve driveability with cool or cold outside temperatures.
Electrical supply for the 2 air heater elements is controlled by the Engine Control Module (ECM) through the 2 air heater relays. Refer to Intake Manifold Air Heater Relays for more information.
Two heavy-duty cables connect the 2 air heater elements to the 2 air heater relays. Each of these cables will supply approximately 95 amps at 12 volts to an individual heating element within the heater block assembly.
Refer to the Powertrain Diagnostic Procedures for an electrical operation and complete description of the intake heaters, including pre-heat and post-heat cycles.
INTAKE MANIFOLD AIR HEATER RELAYS- ECM OUTPUT
Fig. 15 Intake Manifold Air Heater Relays Location:
The 2 intake manifold air heater relays are located in the engine compartment, attached to the left inner fender below the left battery .
The Engine Control Module (ECM) operates the 2 heating elements through the 2 intake manifold air heater relays.
Refer to the Powertrain Diagnostic Procedures for an electrical operation and complete description of the intake heaters, including pre-heat and post-heat cycles.
WAIT-TO-START WARNING LAMP - ECM OUTPUT
The wait-to-start warning lamp is located on the instrument panel.
The wait-to-start warning lamp is turned on and off by the Engine Control Module (ECM) based on inputs from the MAP sensor and the intake manifold air temperature sensor.
The lamp is turned on when the key is first activated. If the ECM reads intake manifold air temperature below 19 °C (66° F), it will turn the wait-to-start warning lamp on for the air heater pre-heat cycle. The lamp stays on until the pre-heat cycle is over.
Refer to the Powertrain Diagnostic Procedures for electrical operation and complete description of the intake heaters, including pre-heat and post-heat cycles.
WATER-IN-FUEL WARNING LAMP - ECM INPUT
The water-in-fuel warning lamp is located on the instrument panel.
The Engine Control Module (ECM) turns on the water-in-fuel warning lamp if water is detected in the diesel fuel. The lamp will illuminate for about two seconds each time the key is initially turned to the ON position as a bulb check.
If the lamp continues to be illuminated, it signals an immediate need for service. Refer to Fuel Filter/Water Separator Removal/Installation for water draining procedures.
Also refer to Water-In-Fuel Sensor - ECM Input for additional information.