Control Unit

On all models except Trooper, ECM is located either under instrument panel left of steering column, or behind driver's side kick panel. On Trooper, ECM is located under center console.

ECM analyzes all electrical data signals from input devices to control fuel injection, ignition and emissions. ECM includes a back-up fail-safe control system. If a malfunction develops in ECM microcomputer, back-up control system will maintain necessary engine functions to permit operation of vehicle. 2.6L, 2.8L and 3.1L engines use an ECM, a separate Programmable Read Only Memory (PROM) calibrator and a Calibration Package (CALPAK).

PROM is factory programmed engine calibration data which "tailors" ECM for specific transmission, engine, emission, vehicle weight and rear axle ratio application. CALPAK provides fuel delivery back-up so engine runs in case of PROM or ECM failure. Any time ECM is replaced, PROM and CALPAK must both be installed into replacement ECM. If battery voltage is removed, PROM and CALPAK information is retained.

On Impulse (non-turbo) and Stylus, ECM calibrations are stored in the Electronic Erasable Programmable Read Only Memory (EEPROM). EEPROM performs functions of PROM and CALPAK, but is not removable from ECM. When replacing ECM, ensure ECM has correct EEPROM for that vehicle. Impulse (turbo) vehicles use an ECM containing a Memory Calibration (MEM-CAL) unit. MEM-CAL unit contains functions of PROM, CALPAK and Electronic Spark Control (ESC) module.

NOTE: Components are grouped into 2 categories. The first category covers INPUT DEVICES, which control or produce voltage signals monitored by the control unit. The second category covers OUTPUT SIGNALS, which are components controlled by the control unit.