BMW DTC P1091 – Pre Catalyst Fuel Trim System Too Lean (Bank 2)
DTC P1091 meaning on BMW
DTC P1091 on a BMW indicates that the Pre Catalyst Fuel Trim System on Bank 2 is reading a lean condition. This means that the engine control module (ECM) has detected that the air-fuel mixture is too lean in the pre-catalyst exhaust stream on the bank 2 side of the engine.
BMW DTC P1091 symptoms
Symptoms of DTC P1091 on a BMW may include:
- Check Engine Light (CEL) illuminated on the dashboard
- Decreased engine performance
- Engine misfires
- Rough idling
- Reduced fuel efficiency
BMW DTC P1091 causes
The possible causes of DTC P1091 on a BMW include:
- Vacuum leaks
- Faulty oxygen sensor
- Fuel delivery issues
- Dirty or clogged fuel injectors
- Exhaust leaks
BMW DTC P1091 seriousness
While DTC P1091 may not cause immediate harm to the engine, it can lead to decreased fuel efficiency and engine performance if left unresolved. Ignoring this fault code may also result in damage to the catalytic converter over time.
How to diagnose DTC P1091 on BMW
To diagnose DTC P1091 on a BMW, a mechanic may perform the following steps:
- Use a diagnostic scanner to retrieve the fault code and freeze frame data
- Inspect for any visible signs of vacuum leaks or exhaust leaks
- Check the oxygen sensor readings and fuel trims
- Perform a fuel pressure test
- Clean or replace the fuel injectors if necessary
How to fix DTC P1091 on BMW
To fix DTC P1091 on a BMW, the following steps may be taken:
- Repair any vacuum leaks or exhaust leaks
- Replace a faulty oxygen sensor
- Address any fuel delivery issues
- Clean or replace clogged fuel injectors
- Reset the ECM and monitor the system for any recurring issues
How to erase DTC P1091 on BMW
To erase DTC P1091 on a BMW, the fault code can be cleared using a diagnostic scanner. After fixing the underlying issue causing the fault code, the ECM can be reset to clear the code. It is important to ensure that the issue has been resolved before clearing the fault code to prevent it from reoccurring.
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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