Engine Coolant Temperature (ECT) sensor circuit high open problem
What the P0118 code means
P0118 is the OBD-II generic code that indicates the Engine Control Module (ECM) has seen the ECT sensor output go more than 4.91 V or less than -40°C (-40°F).
What causes the P0118 code?
The ECT sensor range input to the ECM went to 4.91 or less than -40 deg F indicating an open circuit in the sensor, connector or wiring.
What are the symptoms of the P0118 code?
- The ECM turns the Check Engine Light on and goes into failsafe mode, substituting input to 176 deg F.
- The engine may have a hard start when engine is cold, and start normal when warm.
- The engine may run rough and hesitate until the engine warms up.
- The engine should run close to normal once the engine warms up.
- Note: The symptoms are determined by the manufacturer failsafe ECM strategy for the vehicle during a failure and may vary between manufacturers and vehicles.
How does a mechanic diagnose the P0118 code?
- Inspects for disconnected sensor connectors or damaged connectors
- Scans and documents the codes received and views the freeze frame data to see when the code was set
- Clears the OBD-II fault codes and retests the system to see if the code comes back
- Disconnects the sensor connector and inspects for corrosion or bent pins and repairs as needed.
- Connects the two connector pins together to see if the output on scanner shows above 284 deg F, indicating the wiring is okay, and replaces the ECT sensor
- Above 284 deg F, the circuit has an open circuit in the wiring, connector or ECM and will be fixed by the technician
Common mistakes when diagnosing the P0118 code
- Not visually inspecting the problem area first
- Not following the manufacturer’s pinpoint test procedure step-by-step, and skipping steps
- Replacing the ECT sensor without knowing for sure that it is the problem
- Not connecting it and viewing the ECM data to see if the temperature output from the sensor is as expected before installation of the new ECT sensor
How serious is the P0118 code?
The P0118 code will put the engine ECM to go into a failsafe mode, which may cause the engine to run rough, or hesitate until the engine warms up to operating temperature. The failsafe mode may also cause excessive fuel consumption, carbon fouling of engine components, and various drive complaints, depending on the manufacturer’s failsafe mode strategy. Driving a vehicle for an extended time with the vehicle in failsafe mode may require additional repairs to remove carbon, or repair possible ignition problems. Also, electrical cooling fans may run continuously while the engine is running.
What repairs can fix the P0118 code?
Repairing or replacing the ECT connector
Raping and replacing wiring
open circuit as necessary Replacing the ECT with a new sensor