P0117
System
Powertrain (Fuel/Air)
Scanner required
Enhanced OBD2 scanner (live data graphs, freeze frame, battery voltage test)

Engine Coolant Temperature Sensor Circuit Low Input

Understand P0117, common causes, and the right TOPDON scanner to diagnose it.

ECT circuit shorted low — ECM may think engine is always cold.

Common symptoms

  • Rich running
  • Black smoke
  • Overfueling when warm

Typical causes

  • Short in ECT circuit
  • Failed sensor
  • Corrosion at sensor on cylinder head

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 P0117 with a basic code reader?
P0117 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 P0117?
It depends on the code and symptoms. Flashing check engine lights and misfire codes should be addressed immediately. Consult a professional if unsure.