Engine Control Module: Description and Operation
POWERTRAIN CONTROL HARDWAREPowertrain Control Module (PCM)
The PCM is the control center for the engine powertrain system. The PCM monitors the information from various sensors, and controls the systems that affect the vehicles performance and emissions. The PCM and the transmission control module (TCM) are stand-alone modules. The PCM and the TCM communicate through the high speed control area network (HS CAN). The PCM has a 3 pocket connector assembly with a total of 222 pins. The 74-pin connector is dedicated to chassis related inputs, outputs, powers and grounds. The 98-pin connector is dedicated to engine control related inputs, outputs such as the fuel injectors, camshaft, crankshaft sensors and the turbocharger systems. The 50-pin connector is dedicated to the exhaust aftertreatment components. The PCM receives input from sensors and other electronic components (switches and relays) and places this information into random access memory (RAM) or the electronically erasable programmable read only memory (EEPROM). Based on information programmed into its read-only memory (ROM), the PCM generates output signals to control various relays, solenoids, and actuators. The PCM controls these output circuits by controlling the ground or the power feed circuit through the transistors or an output driver module.
The PCM is located inside the cowl on the right side.
Glow Plug Control Module (GPCM)
NOTE: The wait-to-start indicator on-time is controlled by the powertrain control module (PCM) and is independent from the GPCM on-time.
The glow plug system consists of a GPCM, glow plugs, and the associated wiring harnesses. The glow plug on-time is controlled by the GPCM and functions on the basis of the engines RPM, engines torque, engine coolant temperature, air temperature, BARO sensor and battery voltage. The GPCM is located behind the right hand side front wheel well cover. The GPCM sends power to the individual glow plugs, which it does by duty cycling direct battery voltage. Glow plug on-time normally varies depending on battery voltage and the engine coolant temperature. The power to the glow plugs is provided through the GPCM eight high current drivers from the vehicle battery. Battery power is fed to the GPCM, the power distribution box, then through the vehicle harness, which connects to the GPCM. The ceramic instant start glow plugs can operate up to 20 minutes. The glow plugs may turn back on at cold ambient extended idle. The GPCM provides battery voltage for approximately 2 seconds to rush current and heat up the glow plugs, then drop back to 7 volts lowering the amperage. The module also contains three drivers for the reductant heating system. The GPCM monitors and detects individual glow plug functionality and control. Concerns detected by the GPCM are transmitted to the PCM through the CAN2 circuits.
Electronically Erasable Programmable Read Only Memory (EEPROM)
The PCM stores information in the EEPROM (a memory integrated circuit chip) about vehicle operating conditions, and then uses this information to compensate for component variability.
Power and Ground Signals
Gold and Silver Plated Pins
NOTE: When installing new terminals make sure new gold or silver plated terminals are used where they were originally used.
Some engine control hardware have gold or silver plated pins within the connectors and mating harness connectors to improve electrical stability for low current draw circuits and to enhance corrosion resistance.
Keep Alive Power (KAPWR)
The KAPWR circuit supplies a constant battery voltage (B+) input to the powertrain control module (PCM) to maintain memory contents when the ignition is in the OFF position.
Power Ground (PWRGND)
The PWRGND circuit(s) is directly connected to the battery negative terminal. PWRGND provides a return path for the powertrain control module (PCM) vehicle power (VPWR) circuits.
Reference Voltage (VREF)
VREF is a consistent positive voltage (4.4 to 5.5 volts) provided by the powertrain control module (PCM). VREF is typically used by 3-wire sensors and some digital input signals.
Signal Return (SIGRTN)
The SIGRTN circuit(s) is a dedicated return path for applied components.
Vehicle Buffered Power (VBPWR)
VBPWR is a regulated voltage supplied by the powertrain control module (PCM) to vehicle sensors. These sensors require a constant 12 volts for operation and cannot withstand VPWR voltage variations. VBPWR is regulated to VPWR minus 1.5 volts and is also current limited to protect the sensors.
Vehicle Power (VPWR)
VPWR is the primary source of powertrain control module (PCM) power. VPWR is switched through the PCM power relay and is controlled by the PCM. With the ignition in the START or RUN position, voltage is supplied to the PCM through the ISP-R circuit. When the PCM senses that the ignition is in the START or RUN position, the PCM grounds the PCM relay control (PCMRC) circuit to energize the relay and close the internal contacts. With the relay contacts closed, VPWR is supplied to the PCM.