GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Isuzu 🢒 1998 🢒 S/T Isuzu - 2WD 🢒 DTC 🢒 DTC P0117 Engine Coolant Temperature (ECT) Sensor Circuit Low Voltage

Object Number: 52261 Size: SF
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice
Engine Controls Components
Engine Sensors
OBD II Symbol Description Notice

Circuit Description

The engine coolant temperature (ECT) sensor is a thermistor. The control module supplies the ECT sensor with a reference voltage on the ECT signal circuit and a ground circuit. When the ECT sensor resistance is high, indicating a cold sensor, the ECT sensor signal voltage remains near the supplied voltage. The ECT sensor decreases the signal voltage as the ECT sensor resistance is low, indicating a warm sensor. The control module monitors the ECT sensor signal circuit voltage in order to calculate the engine temperature.

This DTC is designed to detect an ECT sensor signal voltage lower than the possible range of a normally operating ECT sensor.

Conditions for Running the DTC

The engine run time is more than 5 seconds.

Conditions for Setting the DTC

The ECT sensor voltage is less than 0.25 volt for more than 20 seconds.

Action Taken When the DTC Sets
    • The control module illuminates the malfunction indicator lamp (MIL) the first time the diagnostic runs and fails.
    • The control module will set the DTC and records the operating conditions at the time the diagnostic fails. The control module stores the failure information in the scan tools Freeze Frame/Failure Records.

Conditions for Clearing the MIL or DTC
    • The control module turns OFF the MIL after 3 consecutive drive trips when the test has run and passed.
    • A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles. A warm-up cycle occurs when the coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant reaches a temperature that is more than 70°C (158°F) during the same ignition cycle.
    • Use a scan tool in order to clear the DTCs.

Diagnostic Aids

After starting the engine, the ECT sensor temperature should rise steadily to about 90°C (194°F) then stabilize when the thermostat opens.

Check for an intermittent short to ground in the ECT sensor signal circuit by moving the VCM harness at various locations and monitoring the ECT voltage on the scan tool. If the voltage varies, look for a short to ground in the area of the harness that caused the variance.

Use the Temperature vs. Resistance Value Table to test the coolant sensor at various temperature levels in order to evaluate the possibility of a skewed (mis-scaled) sensor. A skewed sensor could result in poor driveability concerns. Refer to Temperature vs Resistance .

An intermittent may be caused by any of the following conditions:

    • A poor connection
    • Rubbed through wire insulation
    • A broken wire inside the insulation

Thoroughly inspect any circuitry that is suspected of causing the intermittent complaint. Refer to Intermittent Conditions in Wiring Systems.

If a repair is necessary, refer to Wiring Repairs .

Test Description

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

  1. If the condition is still present, the ECT sensor voltage will measure less than 0.25 volts.

    2.

  2. This test simulates a high signal voltage condition. If the VCM recognizes the high signal voltage and the scan tool display reads 4 volts or more, the VCM and the wiring are okay. While doing this test additional ECT related DTCs could set.

    3.

  3. This test determines if the ECT sensor signal circuit is shorted to ground.

Step

Action

Value(s)

Yes

No

1

Important: Before clearing the DTCs, use the scan tool Capture Info to save the Freeze Frame and Failure Records for reference. The control module's data is deleted once the Clear Info function is used.

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

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

  1. Install the scan tool.
  2. Turn ON the ignition leaving the engine OFF.
  3. Monitor the ECT sensor voltage on the scan tool.

Does the scan tool display an ECT sensor voltage less than the specified value?

0.25 V

Go to Step 3

Go to Step 5

3

  1. Turn ON the ignition leaving the engine OFF.
  2. Disconnect the ECT sensor harness connector.

Does the scan tool display an ECT sensor voltage more than the specified value?

4.0 V

Go to Step 7

Go to Step 4

4

  1. Turn OFF the ignition.
  2. Disconnect the VCM C2 connector.
  3. Check for a short to ground on the ECT sensor signal circuit.

Did you find a problem?

∞

Go to Step 6

Go to Step 8

5

The DTC is intermittent.

Are any additional DTCs set?

--

Go to the applicable DTC table

Go to Diagnostic Aids

6

Repair the short to ground in the ECT sensor signal circuit. Refer to Wiring Repairs .

Is the action complete?

--

Go to Step 9

--

7

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

Is the action complete?

--

Go to Step 9

--

8
  1. Replace the VCM.
  2. Program the new VCM. Refer to VCM Replacement/Programming .
  3. Perform the VTD Password Learn Procedure. Refer to Password Learn .
  4. Perform the CKP System Variation Learn Procedure. Refer to Crankshaft Position System Variation Learn .

Is the action complete?

--

Go to Step 9

--

9
  1. Using the scan tool, clear the DTCs.
  2. Start the engine.
  3. Allow the engine to idle until the engine reaches normal operating temperature.
  4. Select DTC and the Specific DTC function.
  5. Enter the DTC number which was set.
  6. Operate the vehicle, with the Conditions for Setting this DTC, until the scan tool indicates the diagnostic Ran.

Does the scan tool indicate the diagnostic Passed?

--

Go to Step 10

Go to Step 2

10

Does the scan tool display any additional undiagnosed DTCs?

--

Go to the applicable DTC table

System OK