Faulty engine coolant temperature sensor reading high resistance; Damaged or corroded sensor connector or terminals; Open or high-resistance wire in the sensor signal circuit; Poor ground connection at the sensor or engine block; Corroded or damaged engine computer connector pins; Internal fault in the engine control module (rare)

DTC codes / P01xx · Fuel and air metering / P0118

P0118Engine Coolant Temperature Circuit High Input

Q: What does code P0118 mean?

Engine Coolant Temperature Circuit High Input. P0118 means the engine computer has seen a voltage from the engine coolant temperature (ECT) sensor that is higher than the normal range for the current conditions, which it interprets as an excessively high coolant temperature signal. The computer compares the sensor's voltage to expected values and flags the circuit as a high input fault when the signal stays above the calibrated threshold.

P0118 means the engine computer has seen a voltage from the engine coolant temperature (ECT) sensor that is higher than the normal range for the current conditions, which it interprets as an excessively high coolant temperature signal. The computer compares the sensor's voltage to expected values and flags the circuit as a high input fault when the signal stays above the calibrated threshold.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaFuel and air metering

Symptoms you may notice

Illuminated check engine light, often with no other noticeable symptoms
Temperature gauge reading hotter than normal or pegged at the top
Cooling fan running constantly or not engaging at all, depending on the failure mode
Poor fuel economy or rich-running smell from the exhaust
Hard starting or rough idle when the engine is cold
Reduced engine performance or limp-home mode in some vehicles

Common causes, most likely first

Faulty engine coolant temperature sensor reading high resistance
Damaged or corroded sensor connector or terminals
Open or high-resistance wire in the sensor signal circuit
Poor ground connection at the sensor or engine block
Corroded or damaged engine computer connector pins
Internal fault in the engine control module (rare)

How to diagnose and fix it

Scan all modules and record freeze-frame data to confirm the code and see when it set
Inspect the ECT sensor connector and wiring for corrosion, looseness, or damage
Measure sensor resistance with a multimeter and compare to the manufacturer's temperature-resistance chart
Check the signal circuit for excessive resistance or an open circuit with a multimeter
Verify the sensor ground circuit has low resistance to the engine block
Replace the ECT sensor if resistance is out of specification or the connector is damaged
Clear codes and perform a road test to confirm the repair and that the code does not return

Why a high ECT signal is not always a hot engine

A P0118 can set when the engine is actually cold if the sensor circuit develops high resistance, so do not assume the engine is overheating based on the code alone.
Corroded terminals at the ECT sensor connector are a frequent cause that is often overlooked when the sensor itself tests good.
On some vehicles, a faulty thermostat that sticks open can cause the engine to run cold and set a high-input code because the sensor signal stays in an unexpected range.
The ECT sensor shares its reference voltage and ground with other sensors on many engines, so a fault in a shared circuit can set P0118 along with other sensor codes.
Replacing the sensor without checking the wiring harness often leads to a repeat code when the real problem is an open signal wire.

Can I keep driving with P0118?

You can usually drive the vehicle short distances to a repair shop, but avoid long trips or heavy loads because the computer may be using incorrect temperature data for fuel and fan control. If the temperature gauge shows overheating or you see steam, stop driving immediately to prevent engine damage.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.