EngineLightCodes
Powertrain code

P0117 Engine Coolant Temperature Sensor 1 Circuit Low

Severity
Fix soon
Typical repair cost
$20–$160
Do it yourself
Possible, easy
Shop time
0.3–1.5 hours

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.

How the engine computer detects it

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 (284–320 °F)). 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 gasoline 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 (176 °F); 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.

Written from public technical sources and not yet checked by a mechanic. How we write these pages

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

Common causes

  1. Signal wire shorted to ground (chafing, pinched harness) Most likely
  2. Sensor shorted internally or coolant inside the sensor Most likely
  3. Moisture or coolant in the connector Possible
  4. Engine control module faulty Less likely

How to diagnose P0117

  1. Read every stored code with an OBD-II scanner. If misfire or fuel trim codes are there too, fix those first: they often cause this one.
  2. Inspect the parts involved: engine coolant temperature sensor, engine coolant temperature sensor wiring.
  3. Work through the causes above from most to least likely, cheapest checks first.
  4. Clear the code and drive a full drive cycle to confirm the repair held.

Reading the code

P
Powertrain
0
Generic (SAE) code
1
Fuel and air metering
17
Specific fault

Questions drivers ask

Can I drive with code P0117?

Drive gently and only as far as you need to. The engine computer may limit power to protect the engine, so avoid highways and heavy traffic until it's fixed. If the check engine light starts flashing, pull over.

Will my car pass an emissions inspection with P0117?

Probably not in states that test vehicles with an OBD-II scan: an emissions-related code that keeps the check engine light on is usually an automatic fail. Rules differ by state and county, so check yours.

Will P0117 clear by itself?

The light can go off after several drive cycles without the fault, but the code returns if the cause is still there. After a repair, the readiness monitors need a full drive cycle before an inspection.

Can I fix P0117 myself?

Often yes, with an OBD-II scanner and basic tools. Difficulty: easy. Start with the cheapest checks before replacing expensive parts.

This page is general information, not a substitute for a professional diagnosis. Repair costs are rough estimates for parts and labor and vary by vehicle and region.