B1806 airbag control unit fault

What does error code B1806 mean?

The error code B1806, which primarily occurs in Toyota control units, indicates a specific electrical fault in the circuit of the knee airbag or passenger-side airbag. Technically, this code points to an open circuit (a broken wire) or a short circuit, preventing the control unit from guaranteeing the airbag’s proper functionality.

In detail, B1806—often specified as B1806-1—is listed in Toyota’s error-code databases as “Open Circuit in Knee Airbag Circuit.” The airbag control unit (SRS module) continuously monitors the resistance values of the ignition circuits. If the measured value deviates from the specified tolerances due to a broken wire or corroded contact, this error code is triggered.

As a result, the airbag warning light illuminates to alert the driver, and the affected system is deactivated for safety reasons. The cause is typically a hardware or electrical issue rather than a software problem.

How can you recognize error B1806?

The most obvious symptom of error B1806 is the permanently illuminated airbag or SRS warning light on the instrument panel. Additionally, the control unit may no longer respond to diagnostic requests, or crash data may be stored in the fault memory, preventing normal operation.

The airbag warning light remains on after starting the vehicle and does not extinguish as usual following the system’s self-test. This is a clear indication that the SRS system has detected an active, safety‑relevant fault.

In some cases, the internal fault condition causes the control unit to refuse communication via the diagnostic interface (OBD). Workshops are then unable to read the fault memory, complicating diagnosis.

Often, error B1806 also appears alongside crash data stored in the control unit. After an accident, the device locks up and reports multiple errors until the data is professionally reset.

Why does error code B1806 occur?

The most common cause of B1806 is a physical disruption in the airbag circuit. This includes a broken wire (open circuit), corroded connectors, or a short circuit. Defective components such as seatbelt pretensioners or an internal fault on the control unit’s circuit board can also trigger it.

A broken wire is the primary culprit. Especially in the seat or footwell area, cables can be damaged by mechanical stress (seat adjustments, foot traffic), leading to severed conductors. Corroded connectors likewise reliably interrupt current flow.

A short circuit to ground or to battery voltage can also initiate the fault. Often, this results from damaged cable insulation caused by abrasion against body panels or improper pre-repair work.

Furthermore, a defect may exist within one of the connected airbag components themselves—such as the pyrotechnic initiator of the knee airbag or the seatbelt pretensioner—whose internal resistance no longer meets specifications.

Lastly, an internal fault in the airbag control unit itself can be a contributing factor. Damage to the circuit board from overvoltage, moisture ingress, or damage to the crash memory can disrupt the activation of the relevant airbag circuit and trigger B1806.

Which models experience B1806?

Error code B1806 is a well-known issue affecting numerous Toyota vehicles. Various series and models are impacted, including the Highlander, Corolla, Camry, Estima, and more. At Airbag24, we professionally repair this error code across a wide range of Toyota vehicles.

At Airbag24, we service error code B1806 for the following Toyota models, among others:

Toyota Vitz XP130, Toyota Corolla Wagon, Toyota Corolla Cross, Toyota Camry Hybrid, Toyota Avalon TRD, Toyota Crown Royal, Toyota Aqua Cross, Toyota Highlander XU70 (2019–present), Toyota Estima XR40 (2000–2006), Toyota Estima XR50 (2006–2019), Toyota HiAce Commuter, Toyota Innova Crysta, Toyota Fortuner AN50 (2005–2015), Toyota Etios Liva (2011–2023), and Toyota Porte NNP10.

How is error B1806 professionally repaired?

Repair of error B1806 involves sending in the removed airbag control unit. At Airbag24, technicians perform a comprehensive component-level diagnosis, restore defective hardware, and subsequently erase stored crash data. A final functional test ensures the quality of the repair, which comes with 2 years' statutory liability for defects.

The process begins after removing the control unit from the vehicle and shipping it to Airbag24. It is important to first read out the fault memory and document error code B1806.

In the lab, a detailed visual inspection and electrical measurements are performed. Technicians check the relevant airbag circuits using ohmmeter readings to verify continuity and insulation. The control unit’s circuit board is examined for visible damage, such as burnt components, corroded solder joints, or cracked traces.

The actual electronic repair, if necessary, includes replacing defective SMD components, repairing traces, or substituting fuse resistors. Only after the hardware cause has been conclusively resolved is the crash data record in the control unit’s memory reset.

Finally, a comprehensive functional test is carried out, simulating the SRS system and re-reading the fault memory. The device is only returned once all tests have passed. Airbag24 provides 2 years' statutory liability for defects on all repairs.