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P0128-THERMOSTAT RATIONALITY (CONTINUED) For the Engine circuit diagrams (Refer to 9 - ENGINE - SCHEMATICS AND DIAGRAMS). For a complete wiring diagram Refer to Section 8W. Theory of Operation The PCM predicts what the engine coolant temperature should be, based on the engine coolant temperature at • When Monitored: • Set Condition: Possible Causes LOW COOLANT LEVEL THERMOSTAT OPERATION SIGNAL CIRCUIT SHORTED TO BATTERY VOLTAGE TEMPERATURE SENSOR SIGNAL CIRCUIT OPEN (K900) SENSOR GROUND CIRCUIT OPEN SIGNAL CIRCUIT SHORTED TO GROUND SIGNAL CIRCUIT SHORTED TO (K900), (G931) SENSOR GROUND OTHER POSSIBLE CAUSES PCM Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE - Diagnostic Test 1. ACTIVE DTC NOTE: If any ECT, AAT, CMP or CKP sensor DTCs have set along with P0128, diagnose them before con- NOTE: Make sure that the Pinion Factor has been programmed correctly into the PCM. With a scan tool, read DTCs. Is the DTC active at this time? Yes >> Go To 2 No >> Refer to the INTERMITTENT CONDITION Diagnostic Procedure. Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE) 9 - 140 ENGINE ELECTRICAL DIAGNOSTICS WK |