Faulty engine oil temperature sensor with internal short or drift; Signal wire chafed or shorted to earth in the harness; Water ingress, corrosion or damaged pins in the sensor connector; Oil leaking into the connector or harness, damaging the insulation; Signal wire shorted to the sensor earth return or another earth-side circuit; Fault inside the engine control unit.

P0197

Engine Oil Temperature Sensor A Circuit Low.

Generic
Powertrain
Generic code
Low severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
1: AreaFuel and air metering
97: FaultThe specific fault in that area

What it means

P0197 means the engine control unit has seen the signal voltage from the engine oil temperature sensor fall below the expected range, which it reads as a circuit low fault. This usually points to a short to earth in the signal wiring, a failed sensor, or a wiring or connector fault. The code is set when the signal stays implausibly low (very hot reading) for longer than the calibrated time.

Symptoms

Engine warning light on
Oil temperature gauge or display reading abnormally high, or showing a fault
Engine running in a default or limp strategy on some models
Cooling fan running more than normal on some models
Variable valve timing or oil-temperature-dependent functions behaving oddly
Possible slight increase in fuel consumption or rough running when cold

Possible causes

Faulty engine oil temperature sensor with internal short or driftlikely
Signal wire chafed or shorted to earth in the harnesslikely
Water ingress, corrosion or damaged pins in the sensor connectorpossible
Oil leaking into the connector or harness, damaging the insulationpossible
Signal wire shorted to the sensor earth return or another earth-side circuitpossible
Fault inside the engine control unitrare

How to diagnose

Read all stored codes and freeze frame data, noting engine temperature and whether the fault is current or intermittent
Compare the live oil temperature reading with coolant temperature on a cold engine; they should be similar
Visually inspect the sensor, connector and harness for chafing, oil contamination, corrosion and heat damage
Unplug the sensor with ignition on and check the live reading; it should move towards a very low temperature reading or open-circuit value, and if it stays high the wiring is shorted to earth
Measure the sensor resistance and compare it with the manufacturer's temperature-resistance data for that engine
Check the signal wire for a short to earth and continuity back to the control unit with the battery disconnected
Check the reference voltage and earth at the sensor connector against the wiring diagram
Wiggle test the harness while watching live data to find intermittent faults

How to fix

Replace the oil temperature sensor if its resistance is out of specification
Repair or replace the damaged section of wiring where the signal wire is shorted
Clean or renew the connector and terminals if corroded or contaminated
Fix any oil leak that is contaminating the sensor or harness, then replace affected parts
Clear the code and road test to confirm it does not return
Diagnose the control unit only after wiring and sensor have been fully proven good

Can I keep driving?

Low severity

The car can usually be driven in the short term, but have it checked soon as the control unit may be using a default oil temperature value. If oil pressure or overheating warnings also appear, stop and investigate.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.