P0118
System
Powertrain (Cooling)
Scanner required
Enhanced OBD2 scanner (live data graphs, freeze frame, battery voltage test)

Engine Coolant Temperature Circuit High Input

Understand P0118, common causes, and the right TOPDON scanner to diagnose it.

The ECU sees unrealistically high coolant temperature — often a failed ECT sensor, wiring short, or actual overheating.

Common symptoms

  • Temperature gauge pegged hot
  • Check engine light
  • Possible limp mode or fan always on

Typical causes

  • Failed ECT sensor
  • Short to voltage in sensor circuit
  • Low coolant causing sensor dry-out
  • Actual engine overheating

What scanner do you need?

Enhanced OBD2 scanner (live data graphs, freeze frame, battery voltage test)

Use live data and freeze frame to confirm the fault before replacing parts. ABS, SRS, and network U-codes usually require a full-system scanner.

Diagnostic tips

  • Record freeze frame data when the code first sets
  • Clear the code only after fixing the root cause
  • Check for related pending codes that point to a common issue
  • Verify battery voltage is above 12.4V before chasing sensor codes

Recommended TOPDON scanners

Frequently asked questions

Can I diagnose P0118 with a basic code reader?
P0118 may set in the engine module, but related diagnostics often benefit from an enhanced or full-system scanner with live data and freeze frame.
Is it safe to drive with P0118?
It depends on the code and symptoms. Flashing check engine lights and misfire codes should be addressed immediately. Consult a professional if unsure.