Powertrain, generic · Fuel and air metering

P0117 Engine Coolant Temperature Sensor 1 Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

The engine coolant temperature sensor 1 is an NTC thermistor: the control module feeds 5 V through a resistor, and as the coolant warms the resistance and signal voltage fall. Its value drives cold-start enrichment, idle speed, ignition timing, the radiator fan and the release of closed-loop mixture control. Some Ford engines measure cylinder head temperature instead and calculate a coolant value from it. P0117 means the signal voltage is too low, so the sensor would report an implausibly hot engine (around 140–160 °C). Usual causes are a signal wire shorted to ground, coolant or moisture in the connector, or an internally shorted sensor. Limits: GM below 55 ohms, Ford petrol below 0.244 V for 5 s, Ford diesel below 0.10 V, Mitsubishi below 0.1 V for 2 s. Mitsubishi then calculates with 80 °C; GM/Saab switch the radiator fan on and the A/C compressor off. GM needs two trips. On Ford engines with a head temperature sensor the equivalent is P1290.

Likely causes

Signal wire shorted to ground (chafing, pinched harness)
Sensor shorted internally or coolant inside the sensor
Moisture or coolant in the connector
Engine control module faulty

Symptoms

  • Check engine light on
  • Radiator fan runs constantly
  • Hard cold start (no enrichment, engine reported hot)
  • Temperature gauge at hot end
  • A/C may be switched off

Repair estimate

DifficultyEasyDIY possible
Parts and labour€20–150
Time0.3–1.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

What to check first

  1. Check reading on a cold engine
  2. Inspect for shorts to ground

Parts involved

engine coolant temperature sensorengine coolant temperature sensor wiring

Related codes

P0118P0115P0116P0119P2184

References: law.cornell.edu, gsi.ext.gm.com, fordservicecontent.com, mitsubishitechinfo.com.