What causes fault code P0198?

• Most likely: Faulty Engine Oil Temperature (EOT) sensor – internal open circuit • Likely: Damaged wiring or corrosion in the connector (open circuit on signal or ground wire) • Possible: Defective Engine Control Unit (ECU) – internal AD converter failure • Rare: Engine oil is actually extremely cold (arctic conditions without a heater)

Powertrain (Engine & Gearbox)Standard EOBD

P0198 - Engine Oil Temperature Sensor High

Q: What are the symptoms of fault code P0198?

• No noticeable driveability issues (initially) • Check Engine Light (MIL) illuminated • Inaccurate oil temperature reading on the dashboard • 'Service Now' message or incorrect oil life monitoring • Reduced engine power (Limp mode) on certain models to protect turbochargers

Q: How do you fix fault code P0198?

STEP 1: Inspect the EOT sensor connector for corrosion or loose pins. Clean with contact cleaner if necessary. STEP 2: Use an OBD scanner to check Live Data. If it reads e.g., -40°C, the circuit is open. STEP 3: Measure the reference voltage from the ECU. Unplug the sensor; you should measure 5V between signal and ground. If 5V is missing, check the wiring back to the ECU. STEP 4: Measure the sensor resistance (Ohm). At 20°C (68°F), the value should be approx. 2000-3000 Ohms (check manufacturer spec). If resistance is infinite (O.L), the sensor is faulty. STEP 5: If wiring and sensor are OK, perform a software update or replace the ECU as a last resort.

Last updated:1 February 2026

Related:EOT-sensor, Wiring Harness, ECU/ECM, Instrument Cluster (DIM)

System

Powertrain (Engine & Gearbox)

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Technical Description

Diagnostic Trouble Code (DTC) P0198 indicates that the Engine Control Module (ECM) has detected a high voltage condition in the Engine Oil Temperature (EOT) sensor circuit. This typically occurs when the signal voltage exceeds 4.8V-4.9V for a specific duration. The EOT sensor is an NTC (Negative Temperature Coefficient) thermistor where resistance decreases as temperature increases. High voltage usually signifies an open circuit or a short to power. The ECM relies on this data for engine management strategies such as fuel injection timing, VVT control, and oil life monitoring.

Possible Causes

Faulty Engine Oil Temperature (EOT) sensor – internal open circuit

Damaged wiring or corrosion in the connector (open circuit on signal or ground wire)

Defective Engine Control Unit (ECU) – internal AD converter failure

Engine oil is actually extremely cold (arctic conditions without a heater)

Symptoms

No noticeable driveability issues (initially)

Check Engine Light (MIL) illuminated

Inaccurate oil temperature reading on the dashboard

'Service Now' message or incorrect oil life monitoring

Reduced engine power (Limp mode) on certain models to protect turbochargers

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P0198 - Engine Oil Temperature Sensor High

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P0198 - Engine Oil Temperature Sensor High

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