P0117

DTC P0117 ECT Sensor Circuit Low Voltage




Circuit Description
The Engine Coolant Temperature (ECT) sensor is a thermistor which controls the signal voltage to the Powertrain Control Module (PCM). The PCM supplies a 5 volt reference and a ground to the ECT sensor. Whenever the engine is cold, the ECT sensor resistance will be high.

As the engine warms up, the ECT sensor resistance decreases and the voltage drops. At the normal engine operating temperature, the voltage will be between 1.5 and 2.0 volts.

The engine coolant temperature sensor is one of the inputs used to control the following items:
- The fuel delivery
- The Torque Converter Clutch (TCC)
- The Ignition Control (IC)
- The Evaporative Emission (EVAP) canister purge valve
- The Idle Air Control (IAC) valve

Conditions For Running The DTC
The engine run time is greater than 128 seconds.

Conditions for Setting the DTC
The ECT sensor indicates that the engine cootant temperature is greater than 138 °C (280 °F) for 6.25 seconds.

Action Taken When the DTC Sets
- The Malfunction Indicator Lamp (MIL) illuminates after two consecutive ignition cycles with the malfunction present.
- The PCM records the operating conditions at the time the diagnostic fails. The Freeze Frame and Failure Records buffers stores this information.
- A history DTC is stored.
- The PCM defaults to 20 °C for the first 60 seconds of engine run time. After 60 seconds the ECT will default to 92 °C for engine coolant temperature. The scan tool will not show the defaulted value.

Conditions for Clearing the MIL/DTC
- The MIL will turn off after 3 consecutive ignition cycles in which the diagnostic runs without a fault
- A history DTC will clear after 40 consecutive warm up cycles without a fault
- A scan tool can clear the DTCs

Diagnostic Aids
After the engine has started, the ECT should rise steadily to about 90 °C then stabilize when the thermostat opens.

Steps 1 - 4:

Steps 5 - 9:

Test Description
The number(s) below refer(s) to the step number(s) in the Diagnostic Table.
1. The Powertrain OBD System Check prompts you to complete some of the basic checks and to store the freeze frame and failure records data on the scan tool if applicable This creates an electronic copy of the data captured when this DTC set. The scan tool stores this data for later reference.
4. This step simulates a DTC P0118. The PCM and the ECT wiring are OK if the PCM senses the change in the ECT sensor signal.
7. Reprogram the replacement PCM and perform the crankshaft position system variation learn procedure. Refer to the latest Isuzu Technical Communications System (ITCS) information for PCM programming and the CKP System Variation Learn Procedure for the Crankshaft Position System Variation Learn Procedure.