BMW DTC P1138 – O2 Sensor Heater Circuit Low Voltage (Bank 1 Sensor 2)
DTC P1138 meaning on BMW
The Diagnostic Trouble Code (DTC) P1138 for BMW indicates an issue with the O2 sensor heater circuit having low voltage in Bank 1 Sensor 2. This means that the heating element in the downstream oxygen sensor of the first bank of cylinders is not receiving sufficient voltage to operate properly. The O2 sensor heater circuit is crucial for the sensor to reach its optimal operating temperature quickly, allowing it to provide accurate readings to the engine control module.
BMW DTC P1138 symptoms
Symptoms of DTC P1138 on a BMW may include:
- Check Engine Light (CEL) illuminated on the dashboard
- Decreased fuel efficiency
- Engine running rough or misfiring
- Increased emissions
BMW DTC P1138 causes
The common causes of DTC P1138 on a BMW include:
- Faulty O2 sensor heater circuit
- Wiring or connector issues in the O2 sensor heater circuit
- Blown fuse related to the O2 sensor heater circuit
- Defective engine control module (ECM)
BMW DTC P1138 seriousness
While DTC P1138 may not cause immediate drivability issues, it is important to address this problem promptly. Ignoring this fault can lead to decreased fuel efficiency, increased emissions, and potential damage to the catalytic converter over time.
How to diagnose DTC P1138 on BMW
To diagnose DTC P1138 on a BMW, you can follow these steps:
- Use an OBD-II scanner to retrieve the fault code and verify the specific details of the code.
- Inspect the wiring and connectors related to the Bank 1 Sensor 2 O2 sensor heater circuit for any visible damage or corrosion.
- Check the fuse associated with the O2 sensor heater circuit to ensure it is not blown.
- Test the O2 sensor heater circuit for proper voltage and continuity using a multimeter.
- If necessary, perform a resistance test on the O2 sensor heater itself to determine if it is faulty.
How to fix DTC P1138 on BMW
To fix DTC P1138 on a BMW, you can consider the following solutions:
- Replace the Bank 1 Sensor 2 O2 sensor if it is determined to be faulty.
- Repair or replace any damaged wiring or connectors in the O2 sensor heater circuit.
- Check and replace the fuse if it is blown.
- If the issue persists, consider testing and potentially replacing the engine control module (ECM).
How to erase DTC P1138 on BMW
To erase DTC P1138 on a BMW, you can clear the fault code using an OBD-II scanner. After addressing the underlying issue causing the fault code, you can reset the Check Engine Light by clearing the code with the scanner. Ensure that the repair has been completed successfully before erasing the DTC to prevent the code from reappearing.
Recommended tools & DTC Scanners for BMW
Best Diagnostic App for modern BMWs: BimmerLink
Recommended Bluetooth adapter for Bimmerlink: OBDLink CX
Cable adapter for Bimmerlink: Enet Cable USB Type C
For older BMWs we recommend: Autel AutoLink AL319 (2024 version)
Easy-to-use Multimeter for reliable diagnostics: AstroAI Auto-ranging Multimeter
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