What does it mean?
P1098 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Engine Oil Temperature Sensor Open Circuit . This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms
- Check engine light on with the oil temperature reading missing or pinned at its lowest value
- Oil temperature gauge dead on vehicles that have one
- Oil cooler, fan or service interval strategies stuck in their default state
- Cold-engine fuelling strategies staying active longer than they should on some vehicles
- Slightly raised fuel consumption in those cases
- Frequently no drivability complaint beyond the warning lamp
Likely causes
- Broken signal or ground wire between the sensor and the module
- Connector unplugged, cracked or with a terminal that has backed out
- Sensor element open internally after long service in hot oil
- Severely corroded terminals that no longer make contact
- Harness damaged where it runs near the exhaust, the sump or a moving suspension part
- Poor engine ground point serving the sensor return circuit
- Module input circuit fault as the final possibility
How to fix it
- Read the live oil temperature with the ignition on; an extreme low value with a warm engine confirms the open circuit
- Unplug the sensor and briefly bridge the two connector pins with the ignition on — if the reading swings to maximum, the wiring and module are good
- If nothing changes, check the signal and ground wires for continuity back to the module
- Measure the sensor resistance; an infinite reading condemns the sensor
- Inspect the connector for corrosion, pushed-back terminals and a broken locking tab
- Check the harness route for breaks near heat sources and moving components
- Repair the wiring or fit a new sensor, then confirm the value rises normally through a full warm-up