Circuit Description
The engine coolant temperature (ECT) sensor is a thermistor that controls
signal voltage to the PCM. When the engine is cold, the sensor resistance
is high, therefore the PCM will see high signal voltage. As the engine
warms, sensor resistance becomes less and voltage drops. The voltage
measured across the thermistor is interpreted as a temperature. The
engine coolant temperature gage located in the IP and the PCM share the
same sensor. The PCM interupts the signal from the ECT sensor and then
sends a class II message to the IP (TBCM).
Conditions for Running the DTC
| • | The PCM performs this DTC diagnostic continuously. |
| • | The engine operation time is greater than 8 minutes. |
Conditions for Setting the DTC
| • | The engine coolant temperature is less than or equal to -40°C
(-40°F). |
| • | All of the diagnostic set conditions met for 2 seconds. |
Action Taken When the DTC Sets
| • | The engine coolant temperature gage in the IP will default to
the lowest (coldest) reading. |
| • | The PCM illuminates the malfunction indicator lamp (MIL) on the
second consecutive drive trip that the diagnostic runs and fails. |
| • | The PCM records the operating conditions at the time the diagnostic
fails. The first time the diagnostic fails, the Failure Records will store
this information. If the diagnostic reports a failure on the second
consecutive drive trip, the Freeze Frame records the operating conditions
at the time of failure and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn the MIL off after three consecutive trips without
a fault condition. |
| • | A History DTC clears after forty consecutive warm-up cycles, if
this or any other emission related diagnostic does not report any failures. |
Diagnostic Aids
Important: Remove any debris from the PCM module connector surfaces before servicing
the PCM module. Inspect the PCM module connector gaskets when diagnosing/replacing
the moduel. Ensure that the gaskets are installed correctly. The gaskets
prevent contaminate intrusion into the PCM module.
The engine coolant temperature gage in the IP will default to the lowest
(coldest) reading. Check harness routing for a potential short to voltage.
After engine is started, the ECT temperature should rise steady to about
85°C (185°F). A skewed sensor could result in poor driveability
complaints. Refer to .
