Powertrain, generic · Fuel and air metering

P0115 Engine Coolant Temperature Sensor 1 Circuit

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. P0115 is the general circuit fault without telling low from high. Today it has largely been replaced by P0117, P0118 and P0119; GM and Ford do not set it in the tables checked. Older or individual systems still use it as a collective code, for example Saab Trionic T5 (1998). The circuit is monitored continuously; when it fails, the module uses a substitute value and many systems run the radiator fan permanently.

Likely causes

Connector corroded or loose, terminal spread
Broken or chafed signal or ground wire
Sensor faulty internally (short, open, coolant inside)
Control module input or 5 V supply faulty

Symptoms

  • Check engine light on
  • Poor cold or hot starting
  • Radiator fan runs constantly
  • Higher consumption, rough idle
  • Temperature gauge implausible or dead

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 coolant level
  2. Compare ECT with ambient on a cold engine
  3. Inspect connector

Parts involved

engine coolant temperature sensorengine coolant temperature sensor wiring

Related codes

P0117P0118P0119P0116P2183

References: law.cornell.edu, saabwisonline.com, hella.com.