Airbag control unit with part number AMR4905

What is the function of the AMR4905 airbag control unit?

The airbag control unit with part number AMR4905 is an original equipment manufacturer (OEM) component from Land Rover, serving as the central control unit for the occupant restraint system. It is specifically designed for models such as the Range Rover Classic and P38A, responsible for processing sensor data to deploy airbags and seatbelt pretensioners in the event of a crash.

The AMR4905 control unit is the brain of the passive safety system in certain Land Rover vehicles. It continuously collects and analyzes data from acceleration and crash sensors distributed throughout the vehicle.

In the event of a collision exceeding predefined threshold values, the unit makes the activation decision within milliseconds. It sends ignition signals to the appropriate airbags and seatbelt pretensioners to provide optimal protection for occupants.

After deployment, the unit stores relevant crash data internally, often resulting in a lockout of further functionality.

Why does the AMR4905 control unit fail?

Failures in the AMR4905 airbag control unit are frequently caused by stored crash data following an accident, which prevents further use. Other causes include internal electronic malfunctions or water damage, leading to fault codes such as B1000 (control unit defective), B1001, B1010, B1040, and B1050 in the fault memory.

The most common cause of AMR4905 failure is the retention of crash data after a collision. Even after the vehicle has been repaired, the control unit remains internally locked, and the airbag warning light stays illuminated until this data is professionally reset.

Internal electronic defects represent another source of failure. These can affect components on the circuit board, causing persistent or intermittent system malfunctions. Such issues often manifest as fault code B1000, directly indicating an internal defect in the control unit.

External factors, such as moisture ingress through leaks in the vehicle, can also lead to corrosion on the circuit board and short circuits. This may trigger a range of fault codes, including B1040 or B1050, permanently impairing the unit’s functionality.

How do you recognize a defect in the AMR4905?

A defect in the AMR4905 airbag control unit primarily manifests as a persistently illuminated airbag warning light on the instrument cluster. Additionally, the fault memory often cannot be cleared, and diagnostics reveal specific fault codes such as B1000 (control unit defective) or other associated codes.

The clearest indication of a problem is the continuously lit airbag warning light (SRS light). It fails to extinguish after starting the vehicle, signaling a system-relevant, stored error that compromises safety.

Another symptom is the inability to permanently clear fault codes using a diagnostic tool. Even when a fault is cleared, it often reappears immediately, as the underlying cause—whether hardware failure or stored crash data—remains unresolved.

In some cases, communication with the control unit may be completely disrupted. The diagnostic tool then cannot establish a connection to the AMR4905, complicating troubleshooting and often pointing directly to a severe internal defect in the control unit.

In which vehicles is the AMR4905 installed?

The AMR4905 airbag control unit is an OEM component from Land Rover, used in various classic models of the brand. It is certified for the Rover Range Rover Classic, the Rover Range Rover P38A, and the Rover Range Rover 2.5 TD. At Airbag24, we repair this control unit for the aforementioned model series.

At Airbag24, the AMR4905 control unit is refurbished for the following specific models and series:

Land Rover Range Rover P38A (1994–1998)

Land Rover Range Rover P38A Facelift (1998–2002)

Rover Range Rover Classic

Rover Range Rover P38A

Rover Range Rover 2.5 TD

How does AMR4905 repair proceed at Airbag24?

At Airbag24, AMR4905 repair follows a systematic process. Upon receipt, experienced mechatronics engineers analyze the unit, remove stored crash data, and address any electronic fault sources. Subsequently, full functionality is verified through testing, and you receive 2 years’ statutory liability for defects on the completed repair.

After removal and shipment of the control unit to Airbag24, a comprehensive electronic analysis is first performed. This involves reading out the codes stored in the fault memory and identifying crash data retained on the circuit board.

The actual repair involves professionally erasing the crash data and fixing any hardware defects. This is carried out by experienced technicians to restore the device to its original functionality. The goal is to bring the control unit back to a condition equivalent to that of a new part.

Upon completion of the repair work, the control unit undergoes a final functional test. Should a repair unexpectedly prove impossible, we often offer refurbished and tested replacement control units. We provide 2 years' statutory liability for defects on every successful repair.