GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2002 🢒 GMC C Sierra - 2WD 🢒 Engine 🢒 Engine Controls - 4.3L 🢒 DTC P0125

Circuit Description

An engine coolant temperature (ECT) sensor monitors the temperature of the coolant. This input is used by the powertrain control module (PCM) for engine control and as an enabling criteria for some diagnostics.

The airflow coming into the engine is accumulated and used to determine if the engine has been driven within normal conditions. That is, conditions that would allow the engine coolant to heat up normally to the thermostat regulating temperature. If the coolant temperature does not increase normally or does not reach regulating temperature of the thermostat, problems with the diagnostics may occur. The diagnostics that use ECT as an enabling criteria, may not run when expected.

This diagnostic trouble code (DTC) will only run once per ignition cycle within the enabling conditions.

This DTC will set when there has been excessive time to reach a minimum coolant temperature required for Closed Loop fuel control.

Conditions for Running the DTC
    • DTCs P0100, P0101, P0103, P0110, P0111, P0112, P0113, P0116, P0117, P0118, P0125, P0500, P0501, P0503, P1114, or P1115 are not set.
    • The minimum intake air temperature (IAT) is -7°C (+19°F) or more.
    • The start-up coolant temperature is less than 40°C (104°F).
    • The engine running is more than 2 minutes and less than 17 minutes.
    • The vehicle speed is more than 8 km/h (5 mph) for more than 0.8 km (0.5 mi).
    • The mass air flow (MAF) average reading is more than 15 g/s.

Conditions for Setting the DTC

The Closed Loop coolant temperature of 40°C (104°F) is not reached within a predetermined time.

Conditions for Clearing the MIL/DTC
    • The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
    • 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 emission related diagnostic.
    • Clear the MIL and the DTC with a scan tool.

Conditions for Clearing the MIL/DTC
    • The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
    • 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 emission related diagnostic.
    • Clear the MIL and the DTC with a scan tool.

Diagnostic Aids

DTC P0125 is designed to detect a skewed ECT sensor or a faulty thermostat.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step tests for excessive resistance in the ECT circuit.

    2.

  2. This step tests for a skewed sensor through the range of temperatures affecting this DTC.

Step

Action

Values

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

Is the cooling system low on coolant?

--

Go to Loss of Coolant in Engine Cooling

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Disconnect the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement .
  3. Connect a 3-amp fused jumper wire between the signal circuit and the low reference circuit of the ECT sensor.
  4. Turn ON the ignition, with the engine OFF.
  5. With a scan tool, observe the ECT sensor temperature.

Does the scan tool indicate that the ECT sensor temperature is more than the specified value?

138°C (280°F)

Go to Step 7

Go to Step 4

4
  1. Turn OFF the ignition.
  2. Disconnect the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement .
  3. Connect a 3-amp fused jumper wire between the signal circuit of the ECT sensor and a known good ground.
  4. Turn ON the ignition, with the engine OFF.
  5. With a scan tool, observe the ECT sensor temperature.

Does the scan tool indicate that the ECT sensor temperature is more than the specified value?

138°C (280°F)

Go to Step 5

Go to Step 6

5
  1. Test the ECT sensor low reference circuit for a high resistance or an open. Refer to Circuit Testing in Wiring Systems.
  2. Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 10

--

6
  1. Test the ECT sensor signal low circuit for a high resistance or an open. Refer to Circuit Testing in Wiring Systems.
  2. Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 10

--

7

  1. Remove the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement .
  2. Suspend the ECT sensor and a thermometer in a pan of water.
  3. Place the pan on a burner or hot plate.
  4. Test the resistance of the ECT sensor through the specified range of temperatures.

Does the resistance and temperature closely match the Temperature vs Resistance Table?

10-90°C (50-194°F)

Go to Step 8

Go to Step 9

8

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

Is the action complete?

--

Go to Thermostat Diagnosis in Engine Cooling

--

9

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

Did you complete the replacement?

--

Go to Step 10

--

10
  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 11

Go to Step 2

11

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