What does it mean?
P1186 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: O2 Sensor Heater Circuit (Bank 1-Sensor 1) Electrical Malfunction .
Symptoms
- Check engine light on within a few minutes of a cold start
- Slow transition to closed loop, with rich running and extra fuel used during warm-up
- Mild roughness at idle while the engine is cold
- Reduced fuel economy on short journeys
- Readiness monitors incomplete, so the vehicle fails an emissions inspection
- No noticeable driveability problem once fully warm
Likely causes
- Burnt out or open heater element inside the oxygen sensor, the most frequent cause on higher mileage vehicles
- Blown fuse in the oxygen sensor heater supply
- Heater supply wire broken or chafed against the exhaust
- Corroded or water-filled sensor connector
- Poor ground for the heater circuit
- Failed heater driver in the control module
- Thermal shock damage after driving through deep water
How to fix it
- Check the heater fuse first, especially if more than one heater code is stored
- Measure the heater element resistance across the two heater pins on the sensor side of the connector
- With the ignition on, confirm battery voltage at the heater supply pin of the harness connector
- Verify that the module pulls the heater control wire to ground once the engine is running
- Inspect the harness near the exhaust for heat damage and the connector for corrosion or moisture
- Repair wiring or replace the fuse as required
- Replace the oxygen sensor if the heater element is open or out of specification, then clear codes and confirm the heater monitor completes