What does it mean?
P1187 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 soon after a cold start
- Longer warm-up in open loop with a noticeably rich mixture
- Slight idle roughness while cold, disappearing once warm
- Increased fuel use in stop-start traffic
- Emissions readiness monitors do not complete
- Other heater codes may be stored at the same time
Likely causes
- Open heater winding inside the sensor
- Heater control wire shorted to ground or to battery voltage
- Supply wire broken where the harness passes the exhaust manifold or a heat shield
- Terminal corroded, loose or backed out in the sensor connector
- Shared fuse or relay for the heater circuits has failed
- Failed heater driver stage inside the control module
- Poor module or engine ground affecting the heater control reference
How to fix it
- Read all codes; several heater faults together point to a shared fuse, relay or ground rather than one sensor
- Measure heater element resistance at the sensor and compare with specification
- With the ignition on, check for battery voltage on the heater supply pin of the harness connector
- Test the heater control wire for continuity to the module and for shorts to ground and voltage
- Inspect the harness for heat damage and the connector for corroded or spread terminals
- Repair or replace the damaged wiring and clean the terminals
- Replace the sensor only when the heater element itself is proven faulty, then verify the heater monitor runs on a cold start