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 Setting The DTC
| • | The engine run time is greater than 60 seconds. |
| • | The ECT sensor indicates that the engine coolant temperature is less than -40°C (-40°F). |
Action Taken When the DTC Sets
| • | The Malfunction Indicator Lamp (MIL) illuminates. |
| • | 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 malfunction indicator lamp (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. |
| • | Use a scan tool to clear the DTCs. |
Diagnostic Aids
The normal operating temperature for the engine cooling system is between 90°C (194°F) and 95°C (203°F).
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
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The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information is then stored in the scan tool for later reference.
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This step simulates a DTC P0117. If the PCM senses the change, then the PCM and the ECT wiring are OK.
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Replacement PCMs must be reprogrammed and the crankshaft position system variation procedure must be preformed. Refer to the latest Isuzu Technical Communication System (ITCS) information for programming procedures and also refer to the Powertrain Control Module (PCM) .
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to | ||
2 |
Is the ECT sensor value less than the specified value? | -30°C (-22°F) | ||
3 |
Is the ECT sensor value less than the specified value? | -30°C (-22°F) | Go to Diagnostic Aids | |
Is the ECT sensor value greater than the specified value? | 130°C (266°F) | |||
5 | Connect a jumper wire between the ECT sensor signal circuit terminal (at the ECT sensor electrical connector) and to chassis ground. Is the ECT sensor value greater than the specified value? | 130°C (266°F) | ||
6 | Check for poor connections at the ECT sensor and repair as necessary. Was a repair necessary? | -- | ||
7 | Check the ECT sensor ground circuit for an open and repair as necessary. Was a repair necessary? | -- | ||
8 | Check the ECT sensor signal circuit for an open and repair as necessary. Was a repair necessary? | -- | ||
9 | Check for a poor ECT sensor ground or a poor ECT sensor signal circuit terminal connection at the PCM and replace the terminals if necessary. Did any of the terminal(s) need to be replaced? | -- | ||
10 | Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Is the action complete? | -- | -- | |
Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | -- | ||
12 |
Does the scan tool indicate that this diagnostic has ran and passed? | -- | ||
13 | Check if any additional DTCs are set. Are any DTCs displayed that have not been diagnosed? | -- | Go to applicable DTC table | System OK |
