Circuit Description
The engine coolant temperature (ECT) sensor is a thermistor that is 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, or thermistor, resistance is high and 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 approximately 1.5 to 2.0 volts. DTC P0118 will set when the PCM detects an excessively high signal voltage on the engine coolant temperature sensor signal circuit.
Conditions for Running the DTC
The engine run time is longer than 15 seconds.
Conditions for Setting the DTC
| • | The ECT sensor signal indicates an engine coolant temperature less than -31°C (-24°F). |
| • | The above conditions are present for at least 10 seconds. |
Action Taken When the DTC Sets
| • | The PCM will illuminate the 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 and Fail Records data. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn the MIL OFF during the third consecutive trip in which the diagnostic has been 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 the scan tool Clear Info function or by disconnecting the PCM battery feed. |
Diagnostic Aids
Check for the following conditions:
| • | A poor connection at the PCM |
| Inspect the harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal-to-wire connections. Use a corresponding mating terminal to check for proper terminal tension. |
| • | Damaged harness--If the harness appears to be OK, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the display will indicate the location of the malfunction. Refer to Wiring Repairs . |
| • | A skewed or mis-scaled ECT sensor |
| Refer to Temperature Versus Resistance . |
If DTC P0118 cannot be duplicated, the information included in the Fail Records data can be useful in determining vehicle mileage since the DTC was last set. If the DTC occurs intermittently, performing the DTC P1115 Diagnostic Chart may isolate the cause of the malfunction.
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 | Value(s) | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
1 |
Important: If DTC P1635 5 Volt Reference Circuit is also set, locate and repair the short between the ECT sensor circuit and the 5-volt reference 2 circuit. Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||||||
Is ECT below the specified value? | -38°C or -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 the 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 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 |
