Powertrain Control Module
POWERTRAIN CONTROL MODULEThe center of the On Board Diagnostics II (OBD II) system is a microprocessor called the Powertrain Control Module (PCM). The PCM has a single 88-pin connector. The PCM receives input from sensors and other electronic components (switches, relays, etc.). Based on information received and programmed into its memory, the PCM generates output signals to control various relays, solenoids and actuators.
KEEP ALIVE MEMORY (KAM)
The PCM stores information in Keep Alive Memory (KAM), a memory integrated circuit, about vehicle operating conditions, and then uses this information to compensate for component variability. KAM remains powered when the vehicle ignition key is OFF so that this information is not lost.
FAIL SAFE
This system of special circuitry provides minimal engine operation should the PCM, mainly the Central Processing Unit or EEPROM, stop functioning correctly. All modes of Self-Test are not functional at this time. Electronic hardware is in control of the system while in fail safe operation.
ADAPTIVE FUEL CONTROL STRATEGY
The adaptive fuel control strategy is designed to compensate for variability in the fuel system components. If, during normal vehicle operation, the fuel system is detected to be biased rich or lean, the adaptive fuel control will make a corresponding shift in the fuel delivery calculation.
Whenever an injector or fuel pressure regulator is replaced, KAM should be cleared. This is necessary so the fuel strategy does not use the previously learned adaptive values.
To clear KAM, refer to Testing and Inspection / Procedures / Powertrain Control Module (PCM) Reset.
FAILURE MODE EFFECTS MANAGEMENT
Failure Mode Effects Management (FMEM) is an alternate system strategy in the PCM designed to maintain vehicle operation if one or more sensor inputs fail.
When a sensor input is perceived to be out-of-limits by the PCM, an alternative strategy is initiated. The PCM substitutes a fixed value and continues to monitor the incorrect sensor input. If the suspect sensor operates within limits, the PCM returns to the normal engine running strategy.
ENGINE RPM/VEHICLE SPEED LIMITER
The PCM will disable all of the fuel injectors whenever an engine RPM or vehicle overspeed condition is detected. The purpose of the engine RPM or vehicle speed limiter is to prevent damage to the powertrain. In this strategy, the vehicle will exhibit a rough running engine condition. Once the driver reduces the excessive speed, the vehicle will return to the normal operating strategy.