GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Geo 🢒 1997 🢒 Prizm 🢒 DTC 🢒 DTC P0115 Engine Coolant Temperature (ECT) Sensor Circuit

Schematic Reference: Engine Controls Schematics

Circuit Description

The engine coolant temperature (ECT) sensor is a thermistor. A thermistor is a resistor whose value varies with temperature. The ECT sensor's resistance is high when the coolant temperature is cold, and the ECT sensor's resistance is low when the coolant temperature is warm. The ECT sensor is wired in series with a fixed resistor in the powertrain control module (PCM). The PCM applies 5 volts to the ECT sensor. The PCM monitors the voltage across the ECT sensor and converts the voltage into a temperature reading. The PCM will receive a high voltage input when the coolant temperature is cold. The PCM will receive a low voltage input when the coolant temperature is warm.

Conditions for Running the DTC

The engine is running.

Conditions for Setting the DTC

Temperature input is -40°C (-40°F) for at least 0.5 seconds.

or

Temperature input is 140°C (284°F) for at least 0.5 seconds.

Action Taken When the DTC Sets
    • The PCM illuminates the malfunction indicator lamp (MIL).
    • The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer.
    • The PCM enters the Fail Safe Function in which the coolant temperature will default to 80°C (176°F).

Conditions for Clearing the MIL/DTC
    • The MIL turns OFF after three consecutively passing trips without a fault present.
    • A History DTC clears after 40 consecutive warm-up cycles without a fault.
    • Use the scan tool Clear DTC Information function.

Diagnostic Aids

    • If DTCs P0105, P0110, P0115, and P0120 are also set, the malfunction may be a faulty sensor ground circuit.
    • Check for a faulty electrical connection to the PCM.
    • Check for the proper operation of the engine's cooling system, including the correct coolant level.
    • Use the Temperature vs Resistance table in order to evaluate the possibility of a shifted (incorrectly calibrated) ECT sensor. A shifted sensor could result in a DTC P0115. Refer to Temperature Versus Resistance .

An intermittent malfunction may be caused by a fault in the ECT sensor electrical circuit. Inspect the wiring harness and components for any of the following conditions:

    • Backed out terminals.
    • Improper mating of terminals.
    • Broken electrical connectors locks.
    • Improperly formed or damaged terminals
    • Faulty terminal to wire connections.
    • Physical damage to the wiring harness.
    • A broken wire inside the insulation.
    • Corrosion of electrical connections, splices, or terminals.

Repair any electrical circuit faults that were found. Refer to Wiring Repair in Wiring Systems.

If a DTC P0115 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining vehicle operating conditions when the DTC was first set.

Test Description

The numbers below refer to the step numbers in the Diagnostic Table.

  1. The OBD System Check prompts the technician to complete some basic checks and store the freeze frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.

    2.

  2. This step checks for a high input condition. If the scan tool reads 140°C (284°F) the input circuit may be the result of an short circuit.

    3.

  3. This step checks for a low input condition. If the scan tool reads -40°C (-40°F) the input circuit may be the result of an open circuit.

    4.

  4. This step determines if DTC P0115 is the result of a hard failure or an intermittent condition

Step

Action

Value(s)

Yes

No

1

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

--

Go to Step 2

Go to Powertrain Control Module Connector End Views

2

Select the ECT sensor parameter on the scan tool.

Is the ECT sensor value greater than or at the specified value?

140°C (284°F)

Go to Step 5

Go to Step 3

3

Select the ECT sensor parameter on the scan tool.

Is the ECT sensor value less than or at the specified value?

-40°C (-40°F)

Go to Step 7

Go to Step 4

4

  1. Perform the scan tool Clear DTC Information function.
  2. Place the vehicle into Check Mode, using the scan tool.
  3. Operate the vehicle within the Freeze Frame conditions as noted.

Does the DTC P0115 set?

--

Go to Step 2

Go to Diagnostic Aids

5
  1. Turn ON the ignition, leaving the engine OFF.
  2. Disconnect the ECT sensor electrical connector.
  3. Select the ECT sensor parameter on the scan tool.

Is the ECT sensor value at the specified value?

-40°C (-40°F)

Go to Step 13

Go to Step 6

6
  1. Turn OFF the ignition.
  2. Disconnect the PCM electrical connector at the PCM.
  3. Check the ECT sensor input circuit for a short to ground.

    4. Ensure that the input circuit is not shorted to the sensor ground circuit.

  4. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 15

Go to Step 14

7
  1. Disconnect the ECT sensor electrical connector.
  2. Jump the ECT input circuit and the sensor ground circuit together at the ECT sensor harness connector.
  3. Select the ECT sensor parameter on the scan tool.

Is the ECT sensor value greater than or at the specified value?

140°C (284°F)

Go to Step 9

Go to Step 8

8
  1. Jump the ECT input circuit at the ECT sensor harness connector to chassis ground.
  2. Select the ECT sensor parameter on the scan tool.

Is the ECT sensor value greater than or at the specified value?

140°C (284°F)

Go to Step 10

Go to Step 11

9
  1. Check for faulty electrical connections at the ECT sensor.
  2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 15

Go to Step 13

10
  1. Turn OFF the ignition.
  2. Disconnect the PCM connector at the PCM.
  3. Check the ECT sensor ground circuit for an open.
  4. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 15

Go to Step 12

11
  1. Turn OFF the ignition.
  2. Disconnect the PCM connector at the PCM.
  3. Check the ECT sensor input circuit for an open.
  4. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 15

Go to Step 12

12
  1. Check for a faulty ECT circuit terminal connection at the PCM.
  2. Repair as necessary.

Was a repair necessary?

--

Go to Step 15

Go to Step 14

13

Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement .

Is the action complete?

--

Go to Step 15

--

14

Replace the PCM. Refer to Powertrain Control Module Replacement .

Is the action complete?

--

Go to Step 15

--

15
  1. Clear the scan tool information and road test the vehicle within the Freeze Frame conditions that set the DTC.
  2. Review the scan tool data and check for DTCs. The repair is complete if no DTCs are stored.

Are any DTCs displayed on scan tool?

--

Go to the applicable table

System OK