Engine Control Module: Description and Operation: Overview

PURPOSE
The PCME provides precise control of fuel injection to ensure optimum performance and strict emissions compliance.

OPERATION
The PCME performs system control functions such as fuel injection and ignition timing control. In order to maintain optimum air/fuel ratio through its control of the fuel injection system, the PCME monitors exhaust gas oxygen content by way of input from an oxygen sensor. When adjustments are needed, the PCME varies injector pulse width (ON time) as the means of controlling air/fuel ratio. Factors such as engine temperature, intake air volume and engine speed are also factored into PCME calculations.

LIMP HOME
The system also incorporates a "limp home" mode. When the PCME detects certain sensor failures, it will substitute preprogrammed fixed values in its calculations, permitting continued vehicle operation until repairs can be made. However, the PCME does not substitute a value for engine speed provided by the crankshaft sensor. The engine will not run in the event of crankshaft sensor failure.

TRANSMISSION CONTROL
To coordinate functioning and achieve smooth operation, the PCME provides the electronic transmission control (TCM) with engine speed and load inputs. In return, the TCM provides a signal which causes ignition timing to be momentarily retarded on upshifts. This reduces transmission torque input, resulting in smoother shifts.

SELF DIAGNOSIS
When the PCME detects a fault, the "CHECK ENGINE" lamp on the left side of the instrument cluster will illuminate. It will remain lit with ignition ON until the fault is corrected. A record of the fault is stored in PCME memory as a numbered code. Codes can be displayed on the LCD message display by switching ignition OFF for at least 5 seconds, then switching to position "II" without starting the engine. Press VCM button on trip computer and fault codes will be displayed.

ECU Location:

LOCATION
The engine control module (PCME), located behind the passenger side dash liner, contains a microprocessor and separate electronic component circuits that interface with various input and output devices of the engine management system.