PCM

The powertrain control module (PCM) is located in the passenger compartment below the center console. The PCM controls the following:
- Fuel metering system.
- Transmission shifting (automatic transmission only).
- Ignition timing.
- On-board diagnostics for powertrain functions.


FUNCTION
The PCM constantly observes the information from various sensors. The PCM controls the systems that affect vehicle performance. The PCM performs the
diagnostic function of the system. It can recognize operational problems, alert the driver through the MIL (Service Engine Soon lamp), and store diagnostic
trouble codes (DTCs). DTCs identify the problem areas to aid the technician in making repairs.

The PCM supplies either 5 or 12 volts to power various sensors or switches. The power is supplied through resistances in the PCM which are so high in value that a test light will not light when connected to the circuit. In some cases, even an ordinary shop voltmeter will not give an accurate reading because its resistance is too low. Therefore, a digital voltmeter with at least 10 megohms input impedance is required to ensure accurate voltage readings. Tool J 39200 meets this requirement. The PCM controls output circuits such as the injectors, IAC, cooling fan relays, etc., by controlling the ground or the power feed circuit through transistors or through either of the following two devices:
- Output Driver Module (ODM)
- Quad Driver Module (QDM)

The PCM is designed to maintain exhaust emission levels to government mandated standards while providing excellent driveability and fuel efficiency. The PCM monitors numerous engine and vehicle functions via electronic sensors such as the throttle position (TP) sensor, heated oxygen sensor (HO2S), and vehicle speed sensor (VSS). The PCM also controls certain engine operations through the following:
- Fuel injector control
- Ignition control module
- knock sensor
- Automatic transmission shift functions
- Cruise control
- Evaporative emission (EVAP) purge
- A/C clutch control


IGNITION TIMING
The PCM is responsible for maintaining proper spark and fuel injection timing for all driving conditions. To provide optimum driveability and emissions, the PCM monitors the input signals from the following components in order to calculate spark timing:
- Engine coolant temperature (ECT) sensor.
- Intake air temperature (IAT) sensor.
- Mass air flow (MAF) sensor.
- PRNDL input from transmission range switch.
- Throttle position (TP) sensor.
- Vehicle speed sensor (VSS).
- Crankshaft position (CKP) sensor.

EEPROM
The Electronically Erasable Programmable Read Only Memory (EEPROM) is a permanent memory that is physically soldered within the PCM. The EEPROM contains program and calibration information that the PCM needs to control powertrain operation.


REPROGRAMMING
Reprogramming of the PCM without removing it from the vehicle. This provides a flexible and cost-effective method of making changes in software calibrations. Refer to the latest Techline information on reprogramming or flashing procedures.