Circuit Description
The engine coolant temperature (ECT) sensor is a thermistor mounted in the engine coolant stream. The PCM applies a voltage (about 5.0 volts) through a pull up resistor to the ECT signal circuit. When the engine coolant is cold, the sensor (thermistor) resistance is high, therefore the PCM will measure a high signal voltage. As the engine coolant warms, the sensor resistance becomes less, and the ECT signal voltage measured at the PCM drops. With a fully warmed up engine, the ECT signal voltage should measure about 1.5 to 2.0 volts. When the PCM detects an excessively high signal voltage on the engine coolant temperature sensor signal circuit. DTC P0118 will set.
Conditions for Running the DTC
Engine run time more than 15 seconds
Conditions for Setting the DTC
| • | The ECT sensor signal indicates an engine coolant temperature less than -34°C (-30°F). |
| • | Above condition present for at least 10 seconds. |
Action Taken When the DTC Sets
| • | The PCM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed. |
| • | The PCM will store conditions which were present when the DTC set as Freeze Frame/Failure Records data. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn OFF the malfunction indicator lamp (MIL) during the third consecutive trip in which the diagnostic has run and passed. |
| • | The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction. |
| • | The DTC can be cleared by using a scan tool. |
Diagnostic Aids
Check for the following conditions:
| • | Poor connection at PCM -- Inspect harness connectors for the following conditions: |
| • | Backed out terminals |
| • | Improper mating |
| • | Broken locks |
| • | Improperly formed or damaged terminals |
| • | Poor terminal to wire connection |
| • | Damaged harness -- Inspect the wiring harness for damage. If the harness appears to be OK, observe the ECT display on the scan tool while moving connectors and wiring harnesses related to the ECT sensor. A change in the ECT display will indicate the location of the malfunction. |
| • | Skewed or mis-scaled ECT sensor -- Refer to Temperature Versus Resistance . |
If the DTC cannot be duplicated and is determined to be intermittent, reviewing the Failure Records can be useful in determining when the DTC was last set. Also refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
Test Description
The numbers below refer to the step numbers on the diagnostic table:
-
Verifies that the malfunction is present.
-
This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 |
Important: If DTC P1635 5 Volt Reference Circuit is also set, perform that diagnostic first. Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
Is ECT below the specified value? | -34°C or -30°F | |||
3 |
Does the scan tool indicate DTC P0118 failed? | -- | Go to Diagnostic Aids | |
4 |
Important: If the 3 amp fuse blows, locate and repair the short to voltage on the sensor signal wire and verify that the sensor was not damaged. Is ECT at the specified value? | 140°C or 284°F | ||
5 |
Important: If the 3 amp fuse blows, locate and repair the short to voltage on the sensor signal wire and verify that the sensor was not damaged. Is ECT at the specified value? | 140°C or 284°F | ||
6 |
Was a problem found? | -- | ||
7 |
Was a problem found? | -- | ||
8 |
Was a problem found? | -- | ||
9 |
Was a problem found? | -- | ||
10 | Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Is action complete? | -- | -- | |
|
Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is action complete? | -- | -- | ||
12 |
Does the scan tool indicate DTC P0118 failed? | -- | System OK |
