DTC P0118 Engine Coolant Temperature (ECT) Sensor Circuit High Voltage. Chevrolet Malibu 1999

For 1990-2009 cars only

Makes 🢒 Chevrolet 🢒 1999 🢒 Malibu 🢒 Engine 🢒 Engine Controls - 2.4L 🢒 DTC P0118 Engine Coolant Temperature (ECT) Sensor Circuit High Voltage

Engine Controls Components
Fuel System
OBD II Symbol Description Notice
Powertrain Control Module Connector End Views
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

Circuit Description

The engine coolant temperature (ECT) sensor uses a thermistor in order to control the signal voltage to the Powertrain Control Module (PCM). The PCM supplies a voltage on the signal circuit to the sensor. When the engine is cold, the sensor resistance is high, therefore, the ECT signal voltage will be high.

As the engine warms, the sensor resistance becomes less and the voltage drops. At the normal engine operating temperature, the voltage will be between 1.5 and 2.0 volts at the ECT signal terminal.

The ECT sensor controls the following items:

•	The fuel delivery

•	The torque converter clutch (TCC)

•	The ignition control (IC)

•	The evaporative emission (EVAP) canister purge valve

•	The idle air control (IAC) valve

•	The electric cooling fan

Conditions For Running The DTC

The engine run time is greater than 60 seconds.

Conditions for Setting the DTC

The ECT sensor indicates that the engine coolant temperature is less than -40°C (-40°F) for 6.25 seconds.

Action Taken When the DTC Sets

•	The malfunction indicator lamp (MIL) will illuminate after two consecutive ignition cycles in which the diagnostic runs with the fault active.

•	The PCM will record the operating conditions at the time that the diagnostic fails. This information will store in the Freeze Frame and Failure Records buffers.

•	A history DTC stores.

•	The coolant fan turns ON.

•	The PCM will default to 20°C (68°F) for the first 60 seconds of the engine run time and then to 92°C (198°F).

Conditions for Clearing the MIL/DTC

•	The MIL will turn OFF after three consecutive ignition cycles in which the diagnostic runs without a fault.

•	A history DTC will clear after 40 consecutive warm-up cycles without a fault.

•	The MIL/DTCs can be cleared by using the scan tool.

Diagnostic Aids

•	The normal operating temperature for the engine cooling system is between 90°C (194°F) and 95°C (203°F).

•	Use the Temperature vs. Resistance table in order to evaluate the possibility of a skewed sensor. Refer to Temperature vs Resistance .

Test Description

The number(s) below refer(s) to the step number(s) on the Diagnostic Table.

The Powertrain OBD System Check prompts you to complete some of the basic checks and to store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data captured when the malfunction occurred. The scan tool stores this data for later reference.

This step simulates a DTC P0117. If the PCM senses the change, then the PCM and the ECT wiring are OK.

Reprogram the replacement PCM and perform the crankshaft position system variation learn procedure. Refer to the latest Techline information for PCM programming and the Crankshaft Position System Variation Learn for the Crankshaft Position System Variation Learn Procedure.

DTC P0118-Engine Coolant Temperature (ECT) Circuit-High Voltage

Step

Action

Value(s)

Yes

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

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

Turn ON the ignition switch leaving the engine OFF.
Install a scan tool.

Is the ECT sensor value less than the specified value?

-30°C (-22°F)

Go to Step 4

Go to Step 3

Review the Freeze Frame data and record the parameters.
Start the engine.
Operate the engine within the Freeze frame conditions and Conditions For Running the DTC as specified in the supporting text.

Is the ECT sensor value less than the specified value?

-30°C (-22°F)

Go to Step 4

Go to Diagnostic Aids

Turn OFF the ignition switch.
Disconnect the ECT sensor electrical connector.
Connect a fused jumper wire between the following circuit terminals at the ECT electrical connector:

•	ECT sensor signal circuit terminal

•	ECT sensor ground circuit terminal

Turn ON the ignition switch leaving the engine OFF.

Is the ECT sensor value greater than the specified value?

130°C (266°F)

Go to Step 6

Go to Step 5

Connect a fused jumper wire to the ECT sensor signal circuit terminal at the ECT sensor electrical connector to chassis ground.

Is the ECT sensor value greater than the specified value?

130°C (266°F)

Go to Step 7

Go to Step 8

Turn OFF the ignition switch.
Check for poor electrical connections at the ECT sensor electrical connector.
Repair the electrical connections as necessary.

Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

Go to Step 12

Go to Step 10

Turn OFF the ignition switch.
Check for an open in the ECT sensor ground circuit.
Repair the ECT ground circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

Go to Step 12

Go to Step 9

Turn OFF the ignition switch.
Check the ECT sensor signal circuit for the following conditions:

•	Open circuit

•	Short to voltage

Repair the ECT sensor signal circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

Go to Step 12

Go to Step 9

Check for the following conditions at the PCM electrical connector:

•	Poor ECT sensor ground circuit terminal

•	Poor ECT sensor signal circuit terminal

Replace the terminals as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you need to replace any of the terminal(s)?

Go to Step 12

Go to Step 11

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

Is the action complete?

Go to Step 12

Replace the PCM. Refer to the Powertrain Control Module Replacement .

Is the action complete?

Go to Step 12

Clear the DTCs with the scan tool.
Start the engine.
Idle the engine at the normal operating temperature.
Operate the vehicle within the conditions for running this DTC as specified in the supporting text.

Does the scan tool indicate that this diagnostic has ran and passed?

Go to Step 13

Go to Step 2

Check to see if any additional DTCs are set.

Does the scan tool display any DTCs that you have not diagnosed?

Go to applicable DTC table

System OK