BMW DTC U1139 – Idle-Speed Control Valve / AMT Communication Bus Off
DTC U1139 meaning on BMW
DTC U1139 on a BMW refers to a fault with the Idle-Speed Control Valve / AMT Communication Bus. This diagnostic trouble code indicates a communication issue between the idle-speed control valve and the automated manual transmission (AMT) system.
BMW DTC U1139 symptoms
Symptoms of DTC U1139 on a BMW may include rough idling, stalling, poor acceleration, and potentially even transmission shifting issues. The Check Engine Light may also be illuminated on the dashboard.
BMW DTC U1139 causes
The causes of DTC U1139 on a BMW can vary, but common reasons include faulty idle-speed control valve, wiring issues, poor connections, or problems within the AMT communication bus system.
BMW DTC U1139 seriousness
While DTC U1139 may not always result in immediate drivability issues, it is important to address this fault promptly to prevent potential performance problems and further damage to the vehicle’s systems.
How to diagnose DTC U1139 on BMW
To diagnose DTC U1139 on a BMW, a professional diagnostic scanner capable of reading manufacturer-specific codes is required. The technician will need to inspect the idle-speed control valve, check the wiring and connections, and perform tests on the AMT communication bus to pinpoint the exact cause of the fault.
How to fix DTC U1139 on BMW
Fixing DTC U1139 on a BMW typically involves repairing or replacing the faulty idle-speed control valve, addressing any wiring issues, ensuring proper connections, and resolving any problems within the AMT communication bus system. It is recommended to follow manufacturer guidelines and use OEM parts for the repair.
How to erase DTC U1139 on BMW
Once the underlying issue causing DTC U1139 on a BMW has been fixed, the diagnostic trouble code can be erased using a diagnostic scanner. The technician can clear the code from the vehicle’s memory, and if the repair was successful, the Check Engine Light should no longer be illuminated.
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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