Circuit Description
The engine coolant temperature (ECT) sensor uses a thermistor in order to control the signal voltage to the Powertrain Control Module (PCM). The PCM supplies a voltage on the signal circuit to the sensor. When the engine is cold, the sensor resistance is high and the ECT signal voltage will be high.
As the engine warms, the sensor resistance decreases and the voltage drops. At the normal engine operating temperature, the voltage will be between 1.5 and 2.0 volts at the ECT signal terminal.
The ECT sensor controls the following items:
| • | The fuel delivery |
| • | The torque converter clutch (TCC) |
| • | The ignition control (IC) |
| • | The EVAP canister purge valve |
| • | The idle air control (IAC) valve |
| • | The electric cooling fan |
Conditions For Running The DTC
The engine run time is more than 60 seconds.
Conditions for Setting the DTC
The ECT sensor indicates that the ECT is less than -40°C (-40°F) for 6.25 seconds.
Action Taken When the DTC Sets
| • | The Malfunction Indicator Lamp (MIL) will illuminate after 2 consecutive ignition cycles in which the diagnostic runs with the fault active. |
| • | The PCM will record the operating conditions at the time that the diagnostic fails. This information will store in the Freeze Frame and Failure Records buffers. |
| • | A history DTC stores. |
| • | The coolant fan turns on. |
| • | The PCM will default to 20°C (68°F) for the first 60 seconds of the engine run time and then to 92°C (198°F). |
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. |
| • | Use a scan tool to clear the DTCs. |
Diagnostic Aids
| • | The normal operating temperature for the engine cooling system is between 90°C and 95°C (194°F- 203°F). |
| • | Use the Temperature vs. Resistance table in order to evaluate the possibility of a skewed sensor. Refer to Temperature Versus Resistance . |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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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.
-
The replacement PCM must be reprogrammed and the Crankshaft Position System Variation Learn procedure must be preformed.
Step | Action | Values | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | Go to Step 2 | |||||
2 | Turn on the ignition, leaving the engine off. Is the ECT less than the specified value? | -30°C (-22°F) | Go to Step 4 | Go to Step 3 | ||||
3 |
Is the ECT s less than the specified value? | -30°C (-22°F) | Go to Step 4 | Go to Diagnostic Aids | ||||
Is the ECT more than the specified value? | 130°C (266°F) | Go to Step 6 | Go to Step 5 | |||||
5 | Connect a fused jumper between the ECT sensor signal circuit and ground at the connector . Is the ECT more than the specified value? | 130°C (266°F) | Go to Step 7 | Go to Step 8 | ||||
6 |
Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 10 | ||||
7 |
Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 9 | ||||
8 |
Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 9 | ||||
9 | Inspect for poor connections at the PCM. If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 11 | ||||
10 | Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Did you complete the repair? | -- | Go to Step 12 | -- | ||||
|
Important:: The replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming . Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the repair? | -- | Go to Step 12 | -- | |||||
12 |
Does the DTC reset? | -- | Go to Step 2 | System OK |
