654 airbag control unit fault

What does error code 654 mean in the airbag control unit?

Error code 654, especially as 00654-002, indicates a critical electrical fault in the driver-side seatbelt pretensioner circuit. Variant 00654-007 points to a general, safety‑related internal fault within the airbag control unit. In both cases, the entire restraint system is deactivated for safety reasons.

This diagnostic trouble code (DTC) signals a concrete hardware issue, not a software error. The control unit detects an irregularity in the circuit that prevents proper operation of the connected component, such as the seatbelt pretensioner.

Technically speaking, the control unit can no longer reliably command the component or monitor its status. To prevent potential false activation or failure in an emergency, it shuts down the system and stores the error code in memory.

How do you recognize error code 654?

The primary and unmistakable symptom of error code 654 is the permanently illuminated airbag warning light on the instrument cluster. In related systems, such as VW models equipped with the G85 steering angle sensor, the ESP warning light may also illuminate, and the ESP function could completely fail, further compromising driving safety.

Once the airbag control unit registers error 654, the airbag warning light activates. It remains on even after the engine starts, clearly indicating to the driver that the passive safety system is not operational.

In vehicles fitted with a related part number like 7D0959654, symptoms may extend beyond the airbag system. ESP failure, issues with ECU coding, or error messages such as “signal too large” (e.g., 00588/024C) are typical accompanying signs.

What causes error code 654?

The main cause of error code 654 is an internal hardware defect within the airbag control unit (ACU) itself or a wiring fault leading to the seatbelt pretensioner. This code often appears alongside error code 655. In similar systems, water damage, short circuits, or mechanical wear are also common triggers.

First and foremost is a defect in the electronics inside the control unit. Components on the circuit board responsible for the seatbelt pretensioner circuit may fail due to aging, vibrations, or moisture ingress.

Another frequent cause is damaged cables or corroded connectors between the control unit and the driver-side seatbelt pretensioner. A broken cable or loose connection generates spurious signals that trigger the error code.

Notably, error 654 often occurs in combination with error code 655, suggesting a more complex fault within the control unit. In related systems using similar part numbers, mechanical factors—such as a cracked slip ring on the steering wheel—may also be responsible.

Which vehicles are affected by error code 654?

Error code 654 is particularly well known in specific newer-generation Bentley models, including the Continental Flying Spur, the Continental GTC Speed, and the Flying Spur Speed. At Airbag24, we offer professional repairs for the affected control units of these exclusive vehicles.

At Airbag24, we service the control unit with part number 654 for the following Bentley models:

Bentley Continental Flying Spur Mk3

Bentley Continental GTC Speed Mk3

Bentley Flying Spur Speed Mk3

Although this code is primarily associated with Bentley, similar fault patterns can also occur in other Volkswagen Group vehicles—for example, in the VW T4 when paired with the G85 steering angle sensor (part number 7D0959654).

How is error code 654 professionally repaired?

Professional repair at Airbag24 focuses on fixing the electronic fault directly within the control unit. After submission, the device is thoroughly analyzed, defective components on the circuit board are replaced, and the system undergoes testing. Following reinstallation, clearing the fault memory is mandatory.

The repair process at Airbag24 begins with a detailed diagnosis of the removed control unit. Using specialized measurement equipment, the exact source of the fault on the circuit board is pinpointed—whether it’s a short circuit, water damage, or component failure due to wear.

Subsequently, the defective electronic components are expertly replaced. The emphasis is on durable hardware restoration to fully restore the control unit’s functionality and ensure its original operational reliability.

After repair, the control unit is tested and calibrated on a test bench. This step ensures that all functions operate flawlessly once again. We provide 2 years' statutory liability for defects on the completed repair.

An important note after installation: Error code 654 often remains stored in the fault memory even after the hardware has been repaired. It is therefore essential to clear the fault memory using an appropriate diagnostic tool (e.g., VCDS/OBD) and, if necessary, perform a basic reset to eliminate the error.