DTC P0118 Engine Coolant Temperature (ECT) Sensor Circuit High Voltage. Buick GL7 (Export) 2000

For 1990-2009 cars

### Circuit Description

The engine coolant temperature (ECT) sensor is a thermistor mounted in the engine coolant stream. The powertrain control module (PCM) applies a voltage of about 5.0 volts through a pull-up resistor to the ECT signal circuit. When the engine coolant is cold, the sensor resistance is high and the PCM will measure a high signal voltage. As the engine coolant warms, the sensor resistance decreases and the ECT signal voltage measured at the PCM decreases. With a fully warmed-up engine, the ECT signal voltage should measure about 1.5 to 2.0 volts.

### Conditions for Running the DTC

The engine is running.

### Conditions for Setting the DTC

• | The ECT sensor indicates an engine coolant temperature of less than -39°C (-37°F).

• | The above conditions are present for more than 15 seconds.

### Action Taken When the DTC Sets

• | The PCM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed.

• | The PCM will store conditions which were present when the DTC set as Freeze Frame/Failure Records data.

### Conditions for Clearing the MIL/DTC

• | The PCM will turn OFF the malfunction indicator lamp (MIL) during the third consecutive trip in which the diagnostic has run and passed.

• | The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.

• | The DTC can be cleared by using a scan tool.

### Diagnostic Aids

Inspect for the following conditions:

• | Poor connection at the PCM--Inspect harness connectors for:

- | Backed-out terminals

- | Improper mating

- | Broken locks

- | Improperly formed or damaged terminals

- | Poor terminal-to-wire connections

• | Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

• | A damaged harness. Inspect the wiring harness for damage. If the harness appears to be OK, observe the ECT display on the scan tool while moving the connectors and the wiring harnesses related to the ECT sensor. A change in the ECT display will indicate the location of the fault. Refer to Wiring Repairs in Wiring Systems.

If DTC P0118 cannot be duplicated, the information included in the Failure Records data can be useful in determining the vehicle mileage since the DTC was last set. If it is determined that the DTC occurs intermittently, performing the DTC P1115 Engine Coolant Temperature (ECT) Sensor Circuit Intermittent High Voltage diagnostic may isolate the cause of the fault.

### Test Description

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

1. Verifies that the fault is present.

2. If DTC P0118 can be repeated only by duplicating the Failure Records conditions, refer to the Temperature vs Resistance table. The table may be used to test the ECT sensor at various temperatures in order to evaluate the possibility of a shifted sensor that may be shorted above or below a certain temperature. If this is the case, replace the ECT sensor. If the ECT sensor appears to be OK, the fault is intermittent.

3. This vehicle is equipped with a PCM which utilizes an electrically erasable programmable read-only memory (EEPROM). If the PCM is replaced, the new PCM must be programmed.

#### DTC P0118 - ECT Sensor Circuit High Voltage

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
1 | 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. Turn ON the ignition, leaving the engine OFF.
2. With a scan tool, observe the ECT parameter.

Is the ECT less than the specified value?

-38°C (-36°F)

Go to Step 4

Go to Step 3

3

1. With a scan tool, review and record the Failure Records data.
2. Operate the vehicle within the Failure Records conditions as noted.

Does scan tool indicate DTC P0118 failed this ignition?

--

Go to Step 4

Go to Diagnostic Aids

4 | Test the signal circuit of the ECT sensor for a short to voltage. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 5

5

1. Turn OFF the ignition.
2. Connect a 3 amp fused jumper between the signal circuit of the ECT sensor and the ground circuit of the ECT sensor.
3. With a scan tool, observe the ECT parameter.

Is the ECT more than the specified value?

139°C (282°F)

Go to Step 7

Go to Step 6

6

1. Remove 3 amp fused jumper and connect the jumper between the signal circuit at the ECT sensor and ground.
2. With a scan tool, observe the ECT parameter.

Is the ECT more than the specified value?

139°C (282°F)

Go to Step 8

Go to Step 9

7 | Inspect for faulty connections at the ECT sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 11
8 | Test the ground circuit of the ECT sensor for an open. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 10
9 | Test the signal circuit of the ECT sensor for an open. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 10
10 | Inspect for faulty ground or signal circuit connections at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 12
11 | Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Did you complete the replacement? | -- | Go to Step 13 | --
12 | Important: : The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Did you complete the replacement? | -- | Go to Step 13 | --

13

1. Use the scan tool in order to clear the DTCs.
2. Operate the vehicle within the Failure Records conditions as noted.

Does the DTC reset?

--

Go to Step 2

System OK