C1025 airbag control unit fault

What does error code C1025 mean?

For Mercedes-Benz airbag control units—often bearing part number C1025 themselves—error code C1025 indicates a serious CAN communication fault. Specifically, data transmission between the airbag module (SRS) and the brake assist system (BAS) or the electronic stability program (ESP) is disrupted. The primary cause is usually an internal hardware defect within the airbag control unit itself.

Technically speaking, due to an internal fault, the airbag control unit can no longer send or receive valid signals over the CAN bus. This results in safety-critical systems like BAS and ESP failing to obtain accurate information from the airbag system, impairing their functionality and triggering warning lights.

Although it is classified as a communication error, the root of the problem typically lies not in the wiring between modules but in the airbag control unit’s hardware. Defective components on the circuit board prevent stable communication.

How do you recognize error C1025?

The symptoms of error C1025 are usually clear and directly visible in the vehicle’s cockpit. The main feature is the permanently illuminated warning lights for SRS/Airbag, ESP, and BAS. Additionally, it often becomes impossible to establish diagnostic communication with the airbag control unit, and the ESP function may intermittently fail.

The most noticeable sign is the simultaneous activation of multiple warning lights. The SRS, ESP, and BAS indicator lights remain lit after starting the vehicle and do not turn off, signaling a cross-system fault that directly affects driving safety.

Another clear indication is the complete loss of communication with the airbag control unit. When attempting to read the fault memory using a diagnostic tool, the module no longer responds—it effectively disappears from the diagnostic system.

In some cases, the fault may also manifest as unreliable or completely failed operation of the electronic stability program (ESP), since essential data from the airbag system is missing.

What causes error code C1025?

The primary cause of error code C1025 is an internal hardware defect within the airbag control unit that disrupts CAN-bus communication. Secondary causes can include peripheral issues such as loose connectors or cable damage. Often, this code appears in combination with C1020, B1000, or B2735, which likewise point to a defective control unit.

At the forefront is CAN-bus disruption caused by faulty hardware directly inside the control unit. Defective microprocessors, memory chips, or cold solder joints on the circuit board are among the most common triggers.

In rarer cases, external factors may play a role, including loose connectors at the airbag control unit, damaged cable harnesses, or defects in peripheral components such as the brake light switch, which serves as an inexpensive initial test point.

Error C1025 rarely occurs in isolation; it is frequently accompanied by other codes that confirm the diagnosis. These include additional CAN communication errors like C1020, C1021, and C1024, as well as general control-unit fault codes such as B1000, B1111, B2735, or B2D97.

Which vehicles are affected by C1025?

Error code C1025 is specific to Mercedes-Benz and appears in models equipped with the airbag control unit bearing part number C1025. This covers a range of vehicle classes, including the B-Class (W247), C-Class (W206), CLA (C118), GLE (C292), as well as modern electric vehicles like the EQE (V295) and EQS (X296).

At Airbag24, error code C1025 is professionally repaired across numerous Mercedes-Benz models, including:

Mercedes-Benz B-Class W247 (from 2018), Mercedes-Benz C-Class W206 sedan (from 2021), Mercedes-Benz CLA-Class C118 sedan (from 2019), Mercedes-Benz CLK-Class A208 convertible (1998–2003), Mercedes-Benz GLE-Class C292 SUV (2015–2019), Mercedes-Benz EQE V295 sedan (from 2022), and Mercedes-Benz EQS X296 SUV (from 2022).

How is error C1025 professionally repaired?

A sustainable repair of error C1025 requires refurbishing the removed control unit. After submission to Airbag24, the module undergoes precise component-level diagnostics. Defective parts such as memory chips or solder joints are replaced, and the device is reprogrammed as a “new” module to eliminate any carryover of old faults.

The process begins with the proper removal of the airbag control unit from the vehicle and its secure shipment to a repair specialist. Repair while still installed in the vehicle is not possible.

At Airbag24, a detailed analysis of the circuit board follows to pinpoint the exact source of the fault. Defective electronic components are desoldered and replaced with new, high-quality parts. Subsequently, the control unit is not only cloned but also programmed as a brand-new device to ensure no latent software errors are carried over.

After successful repair and testing, the control unit is returned. Reinstallation must be performed by a qualified workshop. All repairs are covered by 2 years' statutory liability for defects.

What are the benefits of repair?

For fault C1025, repairing the control unit is the most cost-effective and often fastest solution. It offers significant savings compared to a new part, which can cost around €1,500 at Mercedes-Benz, while avoiding the frequent supply shortages of original spare parts.

The key advantage lies in cost: a new Mercedes-Benz airbag control unit is extremely expensive, at approximately €1,500. Repairing it is considerably more affordable and restores full functionality.

Another important factor is availability: original control units from Mercedes-Benz are often not immediately available, leading to long vehicle downtime. Sending the unit in for repair is usually the quicker alternative.

Moreover, refurbishing the original component helps avoid using lower-quality Chinese aftermarket parts with limited durability. Professional repair ensures the component’s longevity and comes with 2 years' statutory liability for defects.