Circuit Description
The engine coolant temperature (ECT) sensor is a thermistor mounted in the engine coolant stream. The powertrain control module (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 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 1.5-2.0 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 is longer than 15 seconds.
Conditions for Setting the DTC
| • | The ECT sensor signal indicates an engine coolant temperature less than -34°C (-30°F). |
| • | The above condition is 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
Inspect for a skewed or mis-scaled ECT sensor.
Refer to Temperature Versus Resistance .
Many situations may lead to an intermittent condition. Perform each inspection or test as directed.
Important: : Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.
| • | Loose terminal connection |
| - | Use a corresponding mating terminal to test for proper tension. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair. |
| - | Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair. |
| • | Damaged harness--Inspect the wiring harness for damage. If the harness inspection does not reveal a problem, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the scan tool display may indicate the location of the fault. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair. |
| • | Inspect the powertrain control module (PCM) and the engine grounds for clean and secure connections. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair. |
If the condition is determined to be intermittent, reviewing the Snapshot or Freeze Frame/Failure Records may be useful in determining when the DTC or condition was identified.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step 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, locate and repair the short between the ECT signal circuit and 5 Volt Reference 1. Did you perform the Powertrain On Board Diagnostic (OBD) System Check? | -- | ||
Is ECT below the specified value? | -38°C (-36°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 (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 (284°F) | ||
6 |
Did you find and correct the condition? | -- | ||
7 |
Did you find and correct the condition? | -- | ||
8 |
Did you find and correct the condition? | -- | ||
9 |
Did you find and correct the condition? | -- | ||
10 | Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Is the action complete? | -- | -- | |
|
Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | -- | ||
12 |
Does the scan tool indicate DTC P0118 failed? | -- | System OK |
