Engine

P0198 — Engine Oil Temperature Sensor Circuit High Input

Severity: medium Drive with care, to a shop

What P0198 means

The engine oil temperature sensor is a thermistor whose resistance changes with heat. The PCM feeds it a 5-volt reference and reads the voltage drop to work out oil temperature. P0198 sets when the signal voltage stays above the expected range, which looks like an open circuit or impossibly cold oil on an engine that is actually warm.

Symptoms

  • Check Engine light is on
  • Oil temperature reading is unrealistic or stuck
  • Reduced power and worse fuel economy
  • Possible limp mode or engine protection
  • Erratic gauge readings if the sensor feeds the instrument cluster

Possible causes

  1. Failed engine oil temperature sensor
  2. Open circuit, corrosion or poor contact in the wiring or connector
  3. Sensor connector left unplugged after an oil change or repair
  4. Signal wire shorted to battery voltage
  5. PCM fault or a problem with the 5-volt reference
  6. Rarely, wrong or badly contaminated oil

How to diagnose

  1. Scan for codes, review freeze frame data and watch oil temperature in live data
  2. Inspect the sensor connector and harness for loose locks, oil, corrosion or damaged insulation
  3. Confirm the connector is fully seated, especially after recent oil service
  4. Unplug the sensor and check for 5 V reference and a good ground
  5. Measure sensor resistance and compare it to the spec for its temperature
  6. Test the signal wire for opens and shorts to voltage
  7. Jumper the connector terminals together: live data should swing to maximum temperature; if not, suspect the wiring or PCM
  8. Test or suspect the PCM only after the sensor and wiring check out

Common fixes

  • Replace the engine oil temperature sensor
  • Repair or replace damaged wiring and connectors
  • Clean the terminals and reseat the connector securely
  • Diagnose, reflash or replace the PCM as a last resort

Questions and answers

Can I drive with a P0198 code?

Briefly, usually yes, but the engine may enter a protection mode. Have the circuit checked soon so you don't miss a real oil overheating problem.

What most often causes P0198?

Most often it's the sensor itself or an open or poor connection in its connector and wiring. Check that the plug is attached if you recently changed the oil.

Do I need a new PCM for P0198?

Almost never as a first step. Test the sensor, wiring and reference voltage first; a PCM failure is rare.

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.