What does it mean?
P1151 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: HO2S Heater Circuit Current Malfunction .
Symptoms
- Malfunction indicator lamp on shortly after a cold start
- Longer than normal open loop operation and poor cold fuel economy
- Slightly rough running while the engine warms up
- Heater fuse blowing occasionally or running visibly discoloured
- Readiness monitors not completing after a drive cycle
Likely causes
- Weak or intermittent relay contact in the heater supply circuit
- Corroded fuse holder or a fuse that has been overheating
- High resistance in the heater feed wire caused by a poor splice or a stretched terminal
- Heater element partially open, drawing less current than the module commands
- Ground path shared with other heaters loosened or corroded
- Voltage drop from a discharged battery or an undercharging alternator
- Aftermarket wiring taps or repairs made in the heater circuit with undersized wire
How to fix it
- Check the heater fuse and its holder for heat discolouration, then test for voltage on both sides with the key on
- Measure available voltage at the sensor connector while the heater is commanded on, not just with the circuit unloaded
- Compare heater resistance against specification at a known ambient temperature
- Perform a voltage drop test along the feed wire and along the ground path with the heater energised
- Inspect any previous repair splices, taps and crimps in the circuit
- Test the relay by substituting a known good identical unit or by checking contact voltage drop
- Repair the supply or ground fault first; replace the sensor only if its element proves out of specification