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Home >> Isuzu >> 1993 >> Stylus Standard >> Repair and Diagnosis (Single Page) >> Engine Performance >> Theory and Operation >> Engine Controls - Theory & Operation - EFI >> Computerized Engine Controls >> Control Unit

Control Unit

On all models, ECM is located either under instrument panel (left of steering column) or behind driver's side kick panel.

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. Vehicles with 3.1L engine use an ECM, a separate Programmable Read Only Memory (PROM) calibrator and a Electronic Erasable Programmable Read Only Memory (EEPROM).

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

On Stylus, ECM calibrations are stored in the Electronic Erasable Programmable Read Only Memory (EEPROM). EEPROM performs functions of PROM, but is not removable from ECM. When replacing ECM, ensure ECM has correct EEPROM for that vehicle.

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.
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