Error code U0401 is displayed and the check engine light is on - what does this mean?
DTC U0401 is recognized by the OBD/EOBD system when there is a communication fault between the engine control unit and the transmission control unit. This error code indicates that the data transmission between these two important vehicle components is interrupted or faulty. The exact designation may vary slightly for different manufacturers, but the basic problem remains the same.
What can cause this error code?
- Defective CAN bus cable between the engine and transmission control unit
- Corroded or loose plug connections
- Damaged engine control unit (ECM/PCM)
- Faulty transmission control unit (TCM)
- Interrupted or short-circuited wiring
- Defective CAN bus terminating resistors
- Power supply problems in the control units
- Software error in one of the control units
What symptoms occur in parallel with fault code U0401?
- Shifting problems: The transmission shifts irregularly or gets stuck in a gear
- Check engine light: The warning light lights up continuously or flashes
- Limp mode: The vehicle switches to emergency running mode with reduced power
- Starting problems: The engine is difficult to start or does not start at all
- Jerking: Unsteady engine running or jerking when accelerating
- Communication errors: Other U-codes may also occur
How can the problem with error code U0401 be rectified?
- Repairing trouble code U0401 requires a systematic approach to diagnosing the communication fault.
- Check and clean plug connections: Check all connections between the engine and transmission control unit for corrosion, looseness or damage and clean or replace if necessary
- Test CAN bus cabling: Use a multimeter to measure the continuity and resistance of the CAN high and CAN low lines and replace damaged cables
- Update control unit software: Have the latest firmware for the engine and transmission control unit installed at authorized workshops
- Check the terminating resistors: Measure the 120 ohm termination resistors on the CAN bus with an ohmmeter and replace defective resistors
- Check the power supply: Check the power supply to both control units and replace any fuses or relays
- Control unit replacement: In the event of irreparable damage, have the defective engine control unit or transmission control unit replaced with a new or overhauled unit
FAQ - Frequently asked questions about DTC U0401
Can I continue driving with error code U0401?
Continuing to drive with code U0401 is only possible to a limited extent. As the communication between the engine and transmission control unit is faulty, the vehicle may switch to emergency mode. Short journeys to the workshop are usually possible, but longer journeys should be avoided.
How much does it cost to repair fault code U0401?
The repair costs for fault code U0401 vary greatly depending on the cause. Simple cable repairs cost 100-300 euros, while replacing a control unit can cost 800-2000 euros. An accurate diagnosis is therefore important.
How can I delete error code U0401 myself?
The EOBD code U0401 can be deleted with an OBD scanner, but will return if the root cause has not been rectified. After the repair, a test drive should be carried out to ensure that the error does not occur again.
Is error code U0401 manufacturer-specific?
The DTC U0401 is a standardized OBD-II code that can occur with different manufacturers. However, the exact meaning can vary slightly, which is why manufacturer-specific diagnostic devices often provide more precise information.
What other codes often appear together with U0401?
Other communication codes such as U0100, U0101 or U0155 often appear together with U0401. These indicate more extensive problems in the CAN bus network and should be diagnosed together.
Can a low battery cause error code U0401?
Yes, a low battery or unstable power supply can cause communication errors between the control units. Before carrying out more complex repairs, the battery voltage and the charging system should be checked.
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