BMW DTC P121B – Crankcase Ventilation Hose Disconnected / Defective (Bank 2)
DTC P121B meaning on BMW
DTC P121B indicates that there is an issue with the crankcase ventilation hose on Bank 2 of the BMW engine. This hose is responsible for allowing excess gases and pressure to escape from the crankcase, helping to maintain proper engine performance and emissions control.
BMW DTC P121B symptoms
Some common symptoms of DTC P121B on a BMW may include rough idling, decreased engine performance, increased fuel consumption, and the illumination of the check engine light on the dashboard.
BMW DTC P121B causes
The most common causes of DTC P121B on a BMW are a disconnected or damaged crankcase ventilation hose on Bank 2. This can lead to leaks, which can disrupt the proper functioning of the engine’s ventilation system.
BMW DTC P121B seriousness
While DTC P121B may not cause immediate engine failure, it is important to address this issue promptly to prevent further damage to the engine and ensure optimal performance and fuel efficiency.
How to diagnose DTC P121B on BMW
To diagnose DTC P121B on a BMW, a mechanic will typically use a diagnostic scanner to retrieve the fault code and then visually inspect the crankcase ventilation hose on Bank 2 for any signs of disconnection or damage. Pressure testing may also be performed to identify any leaks in the system.
How to fix DTC P121B on BMW
To fix DTC P121B on a BMW, the crankcase ventilation hose on Bank 2 will need to be reconnected or replaced if it is found to be defective. It is important to use OEM parts to ensure proper fit and function of the ventilation system.
How to erase DTC P121B on BMW
Once the issue with the crankcase ventilation hose on Bank 2 has been resolved, the DTC P121B fault code can be cleared using a diagnostic scanner. This will reset the check engine light and allow the vehicle’s onboard computer to monitor the system for any new issues.
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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