Engine

P012F — Engine Coolant / Oil Temperature Correlation Fault

Severity: medium Drive with care, to a shop

What P012F means

The engine control unit compares the readings of the coolant temperature sensor and the oil temperature sensor. During warm-up, at operating temperature and while cooling down, the two values should change in a consistent way and stay within an expected difference. P012F is stored when the gap exceeds the calibrated limit for too long. The cause can be a bad sensor or wiring, or a real cooling or oil problem.

Symptoms

  • Check Engine Light on
  • Reduced power as the ECU limits load
  • Erratic or unrealistic temperature gauge readings
  • Possible engine overheating
  • Cooling fan running more than usual or constantly
  • Possible drop in fuel economy

Possible causes

  1. Faulty engine coolant temperature sensor
  2. Faulty engine oil temperature sensor
  3. Open circuit, short or corrosion in sensor wiring or connectors
  4. Low coolant or oil level, or air trapped in the cooling system
  5. Clogged or inefficient oil cooler or heat exchanger
  6. Stuck or faulty thermostat causing uneven warm-up
  7. ECU fault (rare)

How to diagnose

  1. Scan all codes and freeze frame data, and look for other temperature sensor codes
  2. Check coolant and oil levels and condition, and look for leaks
  3. With a fully cold engine, compare both sensor readings on a scan tool; they should be close to ambient temperature
  4. Watch coolant and oil temperature during warm-up and compare with a reference thermometer such as an infrared gun
  5. Inspect sensor connectors and harness for corrosion, damage and contamination
  6. Measure sensor resistance and reference voltage and compare to specifications
  7. Check thermostat and cooling fan operation as the engine reaches operating temperature
  8. Inspect the oil cooler or heat exchanger for restriction and leaks

Common fixes

  • Replace the faulty coolant temperature sensor
  • Replace the faulty oil temperature sensor
  • Repair wiring and connectors, and clean the contacts
  • Top up or replace coolant and oil, and bleed air from the cooling system
  • Replace the thermostat, or flush or replace the oil cooler

Questions and answers

What does P012F mean?

The ECU found too large a difference between the coolant and engine oil temperature readings. It may be a failing sensor or wiring, or a real problem in the cooling or lubrication system.

Can I drive with code P012F?

For a short time, yes, if the gauge looks normal and there are no signs of overheating. If the temperature climbs or power drops, pull over and let the engine cool, or you risk costly damage.

How do I fix P012F?

Start by checking coolant and oil levels, then inspect the wiring and connectors. If those are fine, compare the scan tool readings with real temperatures and replace the sensor that is giving wrong values.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.