BMW DTC P0840 – Transmission Fluid Pressure Sensor/Switch ‘A’ Circuit
DTC P0840 meaning on BMW
DTC P0840 indicates a fault with the Transmission Fluid Pressure Sensor/Switch ‘A’ Circuit in a BMW vehicle. This code is triggered when the powertrain control module (PCM) detects an abnormal signal from the sensor or switch related to the transmission fluid pressure.
BMW DTC P0840 symptoms
Symptoms of DTC P0840 in a BMW may include harsh shifting, transmission slippage, delayed engagement when shifting gears, and in some cases, the transmission may go into a fail-safe or limp mode. The vehicle’s transmission warning light may also illuminate on the dashboard.
BMW DTC P0840 causes
The common causes of DTC P0840 in a BMW include a faulty transmission fluid pressure sensor/switch, wiring issues in the sensor circuit, low transmission fluid level, dirty or contaminated transmission fluid, or a malfunctioning PCM.
BMW DTC P0840 seriousness
Ignoring DTC P0840 in a BMW can lead to further damage to the transmission system, potentially resulting in costly repairs. It is important to address this issue promptly to prevent any long-term damage to the vehicle.
How to diagnose DTC P0840 on BMW
To diagnose DTC P0840 on a BMW, a mechanic would typically start by using a diagnostic scanner to retrieve the fault codes stored in the PCM. They would then inspect the transmission fluid pressure sensor/switch and its wiring for any visible damage or corrosion. Testing the sensor’s resistance and checking the transmission fluid level and condition are also common diagnostic steps.
How to fix DTC P0840 on BMW
Fixing DTC P0840 on a BMW may involve replacing the transmission fluid pressure sensor/switch if it is found to be faulty. Checking and repairing any damaged wiring in the sensor circuit, ensuring the transmission fluid level is correct, and performing a transmission fluid flush and filter replacement if necessary can help resolve the issue.
How to erase DTC P0840 on BMW
Once the underlying issue causing DTC P0840 has been addressed and fixed, the fault codes can be cleared using a diagnostic scanner. This will reset the PCM and turn off the transmission warning light on the dashboard. It is important to verify that the issue has been resolved before clearing the fault codes.
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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