PRELIMINARY INSPECTION
Most engine control system driveability problems result from faulty wiring, poor electrical connections, improper wire routing, or leaking hose connections. Inspect all engine control system components, hoses, connectors and wiring for damage before proceeding with symptom diagnosis.
Malfunction Indicator Light (MIL) should illuminate each time ignition key is turned to ON position with engine off, then go out when engine is started.
PCM is used primarily for charging system, transmission, A/C compressor clutch operation and speed control functions. ECM is used to control fuel and emissions systems.
SYMPTOM DIAGNOSIS
Symptom checks cannot be used properly unless problem occurs while vehicle is being tested. To reduce diagnostic time, ensure steps in appropriate BASIC DIAGNOSTIC PROCEDURES article and SELF-DIAGNOSTICS - RAM PICKUP - DIESEL article were performed before diagnosing a symptom. Following symptoms are available for diagnosis
- «ENGINE DOES NOT START»(ref-158825-S02345549142003102200000)
- «ENGINE DIFFICULT TO START OR WILL NOT START (EXHAUST SMOKES WHILE CRANKING)»(ref-158825-S30898509742003102200000)
- «ENGINE DIFFICULT TO START OR WILL NOT START (NO EXHAUST SMOKE WHILE CRANKING)»(ref-158825-S19606460762003102200000)
- «ENGINE SURGES IN PTO OR CRUISE»(ref-158825-S02720272772003102200000)
- «ENGINE SURGES AT LOW OR HIGH IDLE»(ref-158825-S16203593422003102200000)
- «ENGINE SURGES UNDER LOAD OR IN OPERATING RANGE»(ref-158825-S08105847232003102200000)
- «EXCESSIVE BLACK EXHAUST SMOKE»(ref-158825-S04541834262003102200000)
- «EXCESSIVE BLUE EXHAUST SMOKE»(ref-158825-S00485905102003102200000)
- «EXCESSIVE WHITE EXHAUST SMOKE»(ref-158825-S05204764412003102200000)
INTERMITTENT PROBLEM DIAGNOSIS
Intermittent fault testing requires duplicating circuit or component failure to identify problem. These procedures may lead to PCM setting a Diagnostic Trouble Code (DTC) which may help in diagnosis. For DTC diagnostic information, see SELF-DIAGNOSTICS - RAM PICKUP - DIESEL article.
If problem vehicle does not produce DTCs, monitor voltage or resistance values using a Digital Volt-Ohmmeter (DVOM) while attempting to reproduce conditions causing intermittent fault. A status change on DVOM indicates a fault has been located.
Use a DVOM to pinpoint faults. When monitoring voltage, ensure ignition switch is in ON position or engine is running. Ensure ignition switch is in OFF position or negative battery cable is disconnected when monitoring circuit resistance. Status changes on DVOM during test procedures indicate area of fault.