Powertrain
Generic/SAE
OBD-II Fault Code
P0118: Engine Coolant Temperature Circuit High Input
Meaning, symptoms, likely causes, diagnostic checks and repair guidance for P0118.
Cooling system
Use this category to narrow your checks before replacing parts.
High
Severity is a general guide. Confirm with scan-tool data and vehicle symptoms.
What P0118 usually means
Engine Coolant Temperature Circuit High Input.
Common symptoms
Check Engine light; Poor drivability or reduced fuel economy depending on fault; Temperature gauge abnormal; Overheating or slow warm-up possible
Likely causes
Low coolant; Faulty thermostat; Coolant temperature sensor/wiring fault; Cooling fan issue; High signal voltage; Open ground; Short to voltage; Failed sensor
Diagnostic checks
Scan all modules and record freeze-frame data before clearing codes; Check battery voltage and related fuses; Check coolant level only when engine is cool; Compare scan-tool temperature to actual temperature; Check sensor ground and signal circuit for short to voltage
Repair guidance
Repair leaks, replace thermostat/sensor/fan component after confirming fault; Repair ground/signal circuit or replace confirmed faulty sensor
Verification after repair
Clear code, road-test through the same drive condition, then rescan