Powertrain Control Module

Powertrain Control Module (PCM) monitors engine operating conditions by input received from engine sensors. Control of output actuators determines fuel mixture and idle speed. For PCM location, see POWERTRAIN CONTROL MODULE LOCATION  table.

The engine control system consists of the PCM, relays, modules, sensors, switches and actuators. The PCM sends out electrical reference signals to engine sensors and then analyzes the return signals. The engine sensors supply the PCM with specific information, in the form of electrical signals, to determine engine operating conditions.

PCM uses a memory integrated circuit chip which stores information for Keep Alive Memory (KAM). KAM stores memory of vehicle operating conditions and then uses this information for adaptive learning. KAM remains powered with ignition off so that input and output information is not lost.

Flash Electrically Erasable Programmable Read Only Memory (EEPROM) is an Integrated Circuit (IC) within PCM. IC contains software code required by PCM to control powertrain. EEPROM can be electrically erased and then reprogrammed without removing PCM from vehicle. If a software change is required to PCM, PCM can be reprogrammed through Data Link Connector (DLC) using scan tool.

Only vehicles with cylinder head temperature sensor will have the fail-safe cooling. Fail-safe cooling is activated by PCM only in the event that an overheating condition has been identified. Fail-safe cooling provides engine temperature control when cylinder head temperature exceeds certain limits. Engine temperature is controlled by varying and alternating the number of disabled fuel injectors. This allows all cylinders to cool. When fuel injectors are disabled, their respective cylinders work as air pumps, and this air is used to cool the cylinders. The more fuel injectors that are disabled, the cooler the engine runs, but the engine has less power. Before injectors are disabled, fail-safe cooling alerts driver to a cooling system problem by moving coolant temperature gauge to Red zone. Depending on vehicle, other indicators, such as an audible chime or warning light, are used to alert driver of fail-safe cooling.

In the event that one or more input sensors fail, the PCM initiates an alternative operating procedure called Failure Mode Effects Management (FMEM) to allow the vehicle to maintain driveability. In the event of PCM failure, Hardware Limited Operation Strategy (HLOS) will be activated. HLOS is a system of alternate circuitry that provides minimal engine operation if the PCM fails. During HLOS, all self-test function will stop and system will be controlled by electronic hardware.

Malfunction Indicator Light (MIL) will remain on whenever FMEM or HLOS is in operation. FMEM and HLOS substitute a fixed signal and continue to monitor system failure. If signal(s) return to within operating limits, PCM will resume normal operation.

PCM will disable some or all fuel injectors whenever an engine RPM or vehicle overspeed condition is detected. This prevents damage to the powertrain. Excessive wheel slippage caused by sand, gravel, rain, mud, snow, ice, etc. or excessive and sudden increase in RPM while in NEUTRAL or while driving may cause engine RPM/vehicle speed limiter to be enabled. When engine RPM/vehicle speed limiter has been enabled, vehicle will exhibit a rough running engine condition, and PCM will store DTC P1270. After driver reduces excessive speed, engine will return to normal operating mode. No repairs are required.