For 1990-2009 cars

### Circuit Description

The engine coolant temperature (ECT) sensor is a variable resistor, that measures the temperature of the engine coolant. The powertrain control module (PCM) supplies 5 volts to the ECT signal circuit and a ground for the ECT low reference circuit. When the ECT is cold, the sensor resistance is high. When the ECT increases, the sensor resistance decreases. With high sensor resistance, the PCM detects a high voltage on the ECT signal circuit. With lower sensor resistance, the PCM detects a lower voltage on the ECT signal circuit. If the PCM detects an excessively high signal voltage, which is a low temperature indication, DTC P1115 sets.

### Conditions for Running the DTC

The engine run time is more than 60 seconds.

### Conditions for Setting the DTC

• | The PCM detects an ECT sensor parameter of less than -38°C (-36°F).

• | The intermittent condition exists for a total of 1 second during a 20-second period.

### Action Taken When the DTC Sets

• | The control module stores the DTC information into memory when the diagnostic runs and fails.

• | The malfunction indicator lamp (MIL) will not illuminate.

• | The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records.

• | The driver information center, if equipped, may display a message.

### Conditions for Clearing the DTC

• | A current DTC Last Test Failed clears when the diagnostic runs and passes.

• | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic.

• | Clear the DTC with a scan tool.

### Diagnostic Aids

• | Use the Temperature vs Resistance table in order to test the coolant sensor at various temperature levels in order to evaluate the possibility of a skewed sensor. A skewed sensor could result in poor driveability complaints. Refer to Temperature Versus Resistance .

• | If an intermittent condition is suspected, refer to Intermittent Conditions .

Step | Action | Yes | No
--- | --- | --- | ---
Schematic Reference: Engine Controls Schematics Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views
1 | Did you perform the Diagnostic System Check-Engine Controls? | Go to Step 2 | Go to Diagnostic System Check - Engine Controls
2 | Observe the DTC Info with a scan tool. Is DTC P0118 set? | Go to DTC P0118 | Go to Step 3
3 | With a scan tool, observe the ECT sensor temperature while moving the sensor connector and the PCM connector. Does the scan tool indicate an abrupt change in value? | Go to Step 5 | Go to Step 4
4 | With a scan tool, observe the ECT sensor temperature while moving the wiring harness at the sensor and the PCM. Does the scan tool indicate an abrupt change in value? | Go to Step 6 | Go to Step 7
5 | Repair the connector/terminal as necessary. Refer to Circuit Testing and Connector Repairs in Wiring Systems. Did you complete the repair? | Go to Step 7 | --
6 | Repair the harness/wiring as necessary. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 7 | --
7 |

1. Use the scan tool in order to clear the DTCs.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Did the DTC fail this ignition?

Go to Step 2

Go to Step 8

8 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | Go to Diagnostic Trouble Code (DTC) List | System OK