Powertrain Control Hardware
CONSTANT CONTROL RELAY MODULEThe Constant Control Relay Module (CCRM) (some models) interfaces with the Electronic Engine Control (EC) system to provide Vehicle Power to the Powertrain Control Module (PCM) and the Electronic EC system, and for the control of the cooling fan and A/C clutch. The CCRM also contains the fuel pump relay for fuel pump control or the Fuel Pump Driver Module (FPDM) power supply relay, which supplies power to the FPDM. If any of the internal components of the CCRM fail, the entire unit must be replaced. The descriptions of the specific CCRM functions, as well as the Dual Function A/C high pressure switch and the fuel pump monitor circuit, are found under the individual hardware - PCM inputs and outputs.
FUEL PUMP DRIVER MODULE
The Fuel Pump Driver Module (FPDM) receives a duty cycle signal from the PCM and controls the fuel pump operation in relation to this duty cycle. This results in variable speed fuel pump operation. The FPDM sends diagnostic information to the PCM on the fuel pump monitor circuit.
Natural Gas (NG) Vehicle Module:
NATURAL GAS VEHICLE MODULE
The Natural Gas (NG) vehicle module provides two functions. The first function operates the fuel injectors and is referred to as the Injector Driver Module (IDM). The second function sends a fuel level indicator signal to drive the fuel gauge and is called the Fuel Indicator Module (FIM). IDM NG vehicle fuel indicator driver signals are based on PCM fuel injector driver signals and are controlled directly by the corresponding injector drivers in the PCM. The IDM must be used to provide the NG fuel injectors with the required high current necessary for proper operation. The greater demand of NG fuel injector current warrants an increased size of the injector driver and increased heat dissipation. Given these conditions, the PCM would not be suitable for placement of these drivers. The IDM closely resembles the Electronic Engine Control IV PCM module in appearance.
The IDM injector drivers are capable of controlling the amount of current flow to each NG fuel injector. Once the fuel injector is open, the IDM NG fuel injector driver will reduce current flow sufficient to continue to hold the fuel injector open. This is done by the IDM in an effort to reduce heat. If the IDM driver does not detect the required peak current to initially open the NG fuel injector within a specified amount of time, the IDM driver will drop current to fuel injector hold open current.
The FIM is not part of the powertrain control subsystem and will not be discussed here.
POWERTRAIN CONTROL MODULE
The center of the Electronic EC system is a microprocessor called the PCM. The PCM has a 104-pin electrical connector. The PCM receives input from sensors and other electronic components (switches, relays). Based on information received and programmed into its memory, the PCM generates output signals to control various relays, solenoids and actuators.
KEEP ALIVE RANDOM ACCESS MEMORY
The PCM stores information in Keep Alive Random Access Memory (RAM) (a memory integrated circuit chip) about vehicle operating conditions, and then uses this information to compensate for component variability. Keep Alive RAM remains powered when the ignition switch is off so that this information is not lost.
HARDWARE LIMITED OPERATION STRATEGY
This system of special circuitry provides minimal engine operation should the PCM [mainly the central processing unit or flash electrically erasable programmable read only memory] stop functioning correctly. All modes of Self-Test are not functional at this time. Electronic hardware is in control of the system while in Hardware Limited Operation Strategy (HLOS).
HLOS Allowable Output Functions:
- Spark output controlled directly by the CKP signal.
- Fixed fuel pulse width synchronized with the CKP signal.
- Fuel pump relay energized.
- Idle speed control output signal functional.
HLOS Disabled Outputs To Default State:
- EGR solenoids
- No torque converter clutch lock-up
VARIABLE LOAD CONTROL MODULE
The Variable Load Control Module (VLCM) is used by the Mark VIII for engine cooling fan control and A/C clutch control. In addition to these functions, the VLCM performs diagnostic checks of its system. Information on any failure that is detected by the VLCM is sent via SCP (BUS + and BUS - circuits) to the PCM. This failure information is output as diagnostic trouble codes during electronic engine control Self-Test.
INTEGRATED ELECTRONIC IGNITION SYSTEM
The Integrated Electronic Ignition (EI) System consists of a crankshaft position sensor, coil pack(s), connecting wiring, and PCM. The Coil On Plug (COP) Integrated EI System, used on some models, uses a separate coil for each spark plug and each coil is mounted directly onto the plug. The COP Integrated EI System eliminates the need for spark plug wires but does require input from the camshaft position sensor.
POWER AND GROUND SIGNALS
Vehicle Power
When the ignition switch is turned to the START or RUN position, battery positive voltage (B+) is applied to the coil of the Electronic EC power relay. Since the other end of the coil is wired to ground, this energizes the coil and closes the contacts of the Electronic EC power relay. Vehicle Power (VPWR) is now sent to the PCM and the Electronic EC System as VPWR.
Vehicle Reference Voltage
The vehicle reference voltage is a positive voltage (about 5.0 volts) that is output by the PCM. This is a consistent voltage that is used by the 3-wire sensors.
Mass Air Flow Return
The mass air flow return is a dedicated analog signal return from the MAF sensor. It serves as a ground offset for the analog voltage differential input by the MAF sensor to the PCM.
Signal Return (SIG RTN)
The SIG RTN is a dedicated ground circuit used by most Electronic EC sensors and some other inputs.
Power Ground
Power Ground (PWR GND) is an electric current path return for VPWR voltage circuit. The purpose of the PWR GND is to maintain sufficient voltage at the PCM.
Gold Plated Pins
NOTE: Damaged gold terminals should only be replaced with new gold terminals.
Some engine control hardware has gold plated pins on the connectors and mating harness connectors to improve electrical stability for low current draw circuits and to enhance corrosion resistance. The electronic EC components equipped with gold terminals will vary by vehicle application.