B1655 airbag control unit fault

What does error code B1655 mean?

Error code B1655 indicates a critical coding error in the Airbag Control Module (ACM). This means that the module’s software configuration does not match the vehicle’s specific data. This condition often occurs after replacing the control unit or after crash data has been stored, resulting in deactivation of the airbag system.

B1655 is commonly known in the industry as an “ACM Coding Error.” Technically, the control unit cannot fulfill its assigned role within the vehicle network because it lacks proper programming or the programming is faulty.

Without this vehicle-specific coding, synchronization with other systems and sensors—such as seat occupancy detection or belt tensioners—is impossible. For safety reasons, the system enters a fault mode, and the airbag warning light illuminates.

What symptoms indicate B1655?

The primary symptom of error B1655 is a permanently illuminated airbag warning light on the instrument cluster. Often, standard diagnostic tools cannot clear this error code, leaving it permanently stored. In some cases, communication with the airbag control unit is completely interrupted, making further diagnosis more challenging.

The most obvious sign is the airbag warning light, which remains on after starting the vehicle, alerting the driver that the restraint system is not operational.

Workshops also observe that attempts to clear the fault memory fail—the B1655 code reappears immediately after clearing, clearly indicating a fundamental configuration issue.

What causes B1655?

The most common cause of B1655 is missing or incorrect coding of the airbag control unit, typically following installation of a new or used module. Other triggers include crash data stored in the control unit that prevents reactivation, or faulty software updates. Less frequently, defects in connectors or wiring can disrupt communication.

First and foremost is replacing the airbag control unit without subsequently performing vehicle‑specific programming. Each module must be coded to match the vehicle’s equipment (e.g., number of airbags, belt tensioners).

Following a collision, irreversible crash data is also stored in the control unit’s memory. This data blocks normal functionality and must be professionally erased before the module can be reused.

In addition, other codes may appear in the fault memory, such as U0151 (loss of communication with the airbag control unit), B1000 (internal control unit defect), B1195 (general malfunction of the airbag ECU), or B101C (fault in the seatbelt buckle switch).

Which vehicles are affected by B1655?

Error code B1655 occurs across several manufacturers but is particularly prevalent in various Subaru and Chrysler models. Affected series include the Subaru Legacy, Forester, Outback, Levorg, and the Chrysler Town & Country. For these specific models, repair is often the most cost-effective solution.

At Airbag24, we specialize in repairing error code B1655 for the following models and series:

Chrysler: Town & Country (EV RT)

Subaru: Legacy (BD, BG), Outback (BR), Forester (SK, SK Facelift), BRZ (tS), SVX (CX), Justy (KA), Loyale (AL), XT (AX), XT6 (AX), Levorg (VM, VN), Exiga (YA, YAM, Crossover 7), Stella (RN, LA), R1 (RJ), Pleo (RV), Vivio (KK, KY, Bistro), Sambar (TT, TW, TT1, TT2, Dias), Dias Wagon (S321N, S331N), Chiffon (LA600F), Solterra (Z1X), WRX (STI Type RA, STI S207)

How is B1655 professionally repaired?

Professional repair of error B1655 takes place at the electronic level and focuses on restoring the correct software configuration. After submission, the control unit is read out, vehicle‑specific coding is reinstalled, and any existing crash data is completely erased. Final tests confirm full functionality.

At Airbag24, repairs follow a proven, multi‑step process. First, the removed control unit undergoes a thorough diagnosis to pinpoint the exact cause of the coding error.

The key step is reprogramming the control unit, during which the correct vehicle‑specific data is loaded so the module can once again communicate with the vehicle. If crash data is the root cause, it is irreversibly erased at the chip level.

An additional hardware inspection checks for visible damage to components such as connectors or capacitors. Following successful repair and, if necessary, a firmware update, the control unit is tested on a test bench. You receive 2 years' statutory liability for defects on the completed repair.