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DTC code page

P0115: Engine Coolant Temperature Circuit Malfunction

Quick answer: The ECU sees a basic fault in the engine coolant temperature sensor circuit rather than a believable temperature signal.

Drivers also search this fault as engine coolant temperature circuit malfunction, ECT sensor circuit code, coolant temp sensor circuit fault.

Severity: medium Family: powertrain Related paths: 9
Meaning

What P0115 usually means

P0115 is the broad electrical fault for the engine coolant temperature circuit. It does not say the engine is definitely overheating or running cold. It says the control module has lost confidence in the ECT circuit itself because the signal, reference, or wiring no longer behaves like a normal temperature input.

Fast triage

Start here before chasing parts

  • Scan first: save freeze-frame and pending codes before clearing anything.
  • Confirm the complaint: compare the stored code with current drivability symptoms.
  • Use context: trims, live data, and related codes usually narrow the fault faster than guesswork.
  • Work simplest to hardest: leaks, connectors, maintenance items, and known patterns before expensive components.
Initial checks

What to check first

  • Read coolant temperature on a cold engine and compare it with ambient temperature before clearing anything.
  • Inspect the ECT connector for coolant contamination, bent pins, or brittle locking tabs.
  • Look for companion rationality codes like P0116, low-input P0117, or high-input P0118 because they usually narrow the failure path faster.
Driving risk

Can you keep driving?

Short-term driving is sometimes possible, but bad ECT data can skew fueling, fan control, and warm-up strategy. If the fan is running constantly, the engine starts poorly, or the gauge behaves oddly, diagnose it soon.

Moderate urgency: This code often allows short-term driving, but the right fix usually comes faster when you diagnose it early instead of waiting for more codes.
Likely causes

Common causes behind this code

  • Failed engine coolant temperature sensor internally
  • Open, shorted, or high-resistance ECT wiring
  • Loose or corroded sensor connector
  • Shared reference-voltage or ground problem affecting the circuit
  • Rare PCM input fault after wiring and sensor checks

Cause phrases often tied to this code: bad coolant temp sensor, open or shorted wiring, poor connector contact, 5-volt reference issue, ground fault.

Diagnostic order

Suggested workflow

  1. Compare scan-tool coolant temperature to actual ambient temperature after the vehicle has sat overnight.
  2. Inspect the sensor connector and wiring near the thermostat housing or coolant outlet for rub-through and coolant contamination.
  3. Verify the sensor has the correct reference and ground before condemning the sensor itself.
  4. Wiggle-test the harness while watching live data for sudden jumps or dropouts.
  5. If the circuit checks out electrically, confirm the PCM is interpreting the sensor signal correctly.
Avoid guesswork

Common mistakes

  • Replacing the thermostat for a circuit code before checking the sensor signal and wiring.
  • Ignoring freeze-frame temperature because it reveals whether the fault happened at cold start or fully warm.
  • Assuming the dash gauge alone proves the ECU sees the same temperature value.
Repair path

Practical fix guidance

  • Repair the circuit fault first: connector, wiring, reference, ground, or sensor as testing proves.
  • After the repair, cold-soak the car and confirm the coolant reading starts near ambient and climbs smoothly during warm-up.
  • Retest for related rich, lean, thermostat, or catalyst warm-up codes because bad ECT data often triggers them secondarily.
Vehicle context

Affected brands in this MVP

Brand hubs help broaden internal linking now and can evolve into make-specific diagnostic notes later.

Aliases and common searches

English phrases tied to P0115

Useful when the driver knows the wording but not the exact DTC yet.

  • engine coolant temperature circuit malfunction
  • ECT sensor circuit code
  • coolant temp sensor circuit fault
Related search intent

Queries this page can answer naturally

  • P0115 code meaning
  • what does P0115 mean
  • coolant temp sensor circuit malfunction
  • ECT circuit fault symptoms
FAQ

Quick questions about P0115

Is P0115 the same as a bad thermostat?

No. P0115 is a circuit fault around the coolant temperature input, while thermostat faults more often show up as rationality or warm-up codes like P0128.

Can P0115 cause poor fuel economy?

Yes. If the ECU is fed bad coolant data, it may enrich the mixture longer than needed or run the fans abnormally.

Should I replace the sensor first?

Only after checking the connector, reference voltage, and ground. Many P0115 faults are in the circuit around the sensor, not the sensor element alone.