GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Oldsmobile 🢒 2001 🢒 Alero 🢒 DTC 🢒 DTC P1115

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 lowers. 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 5 seconds.

Conditions for Setting the DTC

The PCM detects an intermittent low ECT sensor temperature when the engine is running and when the run time exceeds 5 seconds.

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
    • An intermittent open or short to voltage in the ECT sensor signal circuit could result in a DTC P1115. If the high ECT voltage reading is present, indicating a low temperature, additional sensor circuit voltage codes could be set. Refer to any non-intermittent DTCs that are set.
    • Use the Temperature vs Resistance value 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 you suspect an intermittent condition, refer to Intermittent Conditions .

Test Description

The number below refers to the step number on the diagnostic table.

  1. If there is no driveability condition associated with DTC and if the DTC does not reset, then the system is OK.

Step

Action

Yes

No

Schematic Reference: Engine Controls Schematics

1

Did you perform the Diagnostic System Check-Engine Controls?

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2
  1. Install a scan tool.
  2. Turn ON the ignition.
  3. Start the engine.

Does the scan tool indicate that DTC P0118 also failed?

Go to DTC P0118

Go to Step 3

3
  1. Turn ON the ignition, with the engine OFF.
  2. 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 6

Go to Step 4

4
  1. Turn ON the ignition, with the engine OFF.
  2. 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 7

Go to Step 5

5

  1. Observe the Freeze Frame/Failure Records data for this DTC.
  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 or as close to the Freeze Frame/Failure Records data that you observed.

Does the DTC reset ?

Go to Diagnostic Aids

System OK

6

Repair the connector and the terminal as necessary. Refer to Circuit Testing and Connector Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 8

--

7

Repair the harness and the wiring as necessary. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 8

--

8
  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.

Does the DTC run and pass?

Go to Step 9

Go to Step 2

9

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