B1520 airbag control unit fault

What does error code B1520 mean in the airbag control unit?

Error code B1520 primarily indicates an open circuit or a fault in the hood switch circuit. As a result, the airbag control unit (SRS module) cannot receive signals from this switch, or receives only incorrect signals, leading to deactivation of the entire airbag system to prevent malfunctions.

Technically speaking, the control unit continuously monitors the status of critical sensors and switches. If an open circuit, an implausible signal, or a short circuit is detected in the hood switch circuit, the system interprets this as a critical fault.

The control unit then illuminates the airbag warning light and stores error code B1520 in the fault memory. This condition persists until the underlying cause is resolved and the fault memory is cleared.

How can you recognize error B1520?

The most obvious symptom of error code B1520 is the permanently illuminated airbag warning light (SRS warning lamp) on the instrument panel. Additionally, as a safety precaution, the airbag system is completely disabled, which poses a significant risk in the event of a crash since no airbags will deploy.

The warning light does not extinguish after starting the vehicle as usual but remains constantly lit, clearly indicating to the driver that there is a problem with the restraint system and that immediate diagnosis is required.

In some cases, communication issues with the airbag control unit may also occur when diagnostic tools attempt to access the module. However, this depends on the specific nature of the fault.

Possible causes of error code B1520

The causes of B1520 are usually found in the peripheral components of the control unit. Common issues include broken cables, corroded connectors, or a defective hood switch itself. Less frequently, internal short circuits within the control unit caused by moisture may also be responsible.

One of the most frequent causes is a physical break in the wiring harness leading to the hood switch. Vibrations, aging, or damage caused by animals such as martens can compromise the wires and disrupt the electrical circuit.

Defective or corroded connectors are another typical source of failure. Moisture and dirt in the engine compartment can attack the contacts, significantly increasing electrical resistance and preventing proper signal transmission.

The hood switch itself can also fail mechanically or electrically. An internal defect in the switch results in the inability to send a clean signal to the airbag control unit.

In rarer cases, ingress of moisture can cause a short circuit on the circuit board of the airbag control unit, which may likewise lead to storage of error code B1520.

In which vehicles does error B1520 occur?

Error code B1520 is particularly well-known in certain models from Fiat and Chevrolet. However, it can also appear in other vehicles that use a similar system architecture for monitoring the hood. The models listed here are familiar to us from repair experience.

At Airbag24, we repair error code B1520 for the following specific vehicle models, among others:

Fiat: Fullback series 344 (model years 2016–2020)

Chevrolet: Bolt EV, first generation (model years 2016–2021)

How is error B1520 professionally repaired?

Professional repair begins with a systematic fault search involving cables, connectors, and sensors. If the cause is an internal defect or if crash data has been stored, the control unit is read out, errors are cleared, and damaged electronic components on the circuit board are either repaired or replaced.

At Airbag24, repairs follow a proven procedure after submission of the removed control unit. First, the fault memory is read using specialized diagnostic equipment to verify error code B1520 and any stored crash data.

This is followed by an electronic analysis of the circuit board. Our technicians inspect relevant circuits for shorts, breaks, or damage caused by overvoltage. Defective components are expertly replaced.

A key step is the targeted clearing of error messages and any crash data that may have locked the control unit after an accident. Following restoration, the module is thoroughly tested to ensure it is fully functional again.

We provide 2 years' statutory liability for defects on every repair. Work on the airbag system must be performed exclusively by trained specialists, as improper handling can be life‑threatening.

Is Repairing the Control Unit Worth It?

Yes, in most cases, repair is the most cost-effective solution. It is significantly cheaper than purchasing a new part from the manufacturer and restores the original component’s full functionality. This also eliminates the need for time-consuming reprogramming of the vehicle.

The cost of a new airbag control unit can be substantial, depending on the vehicle model. A professional repair typically saves 50–70% compared to the price of a new unit, without compromising safety or functionality.

Since the original control unit remains intact and is simply refurbished, it is ready to use immediately after installation (plug-and-play). Two years' statutory liability for defects on the completed repair provides added peace of mind.