Airbag control unit with part number K851M-EH100

What is the function of the Airbag Control Unit K851M-EH100?

The Airbag Control Unit K851M-EH100 is the central control unit of the Occupant Restraint System (SRS) in the Infiniti M45 Y50. It processes data from acceleration sensors in real time to detect a collision and, when necessary, precisely deploy the airbags and seatbelt pretensioners at the optimal moment. Its proper functioning is critical for passive vehicle safety.

As the “brain” of the safety system, the K851M-EH100 continuously monitors all connected components—from crash sensors located at the front and sides of the vehicle to the ignition circuits of individual airbags and seatbelt pretensioners. Mounted near the vehicle’s center of gravity, typically in the center tunnel, it can accurately measure the forces generated during a collision.

In the event of an accident, the control unit makes split-second decisions on which restraint systems need to be activated to provide maximum protection for occupants. After deployment, the unit locks itself for safety reasons and permanently stores crash data, necessitating repair or a reset.

Why does the Airbag Control Unit K851M-EH100 fail?

The most common cause of failure for the K851M-EH100 is the storage of crash data following an accident, resulting in permanent lockout. Additionally, internal hardware defects—such as memory errors (EEPROM/Flash), faulty voltage regulators, or issues with the microcontroller—are typical causes requiring electronic repair.

A key reason for service is deliberate deactivation of functionality after airbag deployment. The control unit retains crash-event data and enters a safety mode indicated by the illuminated airbag warning light. This condition can only be resolved through a targeted reset of stored data performed by a specialized service provider.

Electronic faults on the circuit board are another frequent source of failure. These include defective components in the internal power supply, such as DC/DC converters or voltage regulators. The memory chip itself (EEPROM) or the main processor may also fail, often leading to complete communication loss.

External factors like moisture or water damage can cause corrosion at connectors and on the circuit board. Likewise, material fatigue due to age or vibrations can result in microscopic cracks at BGA and SMD component solder joints, impairing the control unit’s functionality.

Symptoms: How do you recognize a defective K851M-EH100?

A defect in the K851M-EH100 Airbag Control Unit primarily manifests as a persistently illuminated airbag or SRS warning light on the instrument cluster. Other clear indicators include fault codes stored in the error memory—such as “control unit defective” or “crash data stored”—as well as complete loss of communication with diagnostic equipment.

The most obvious symptom is the constantly lit airbag warning light. It fails to extinguish after starting the vehicle, signaling a serious, safety-critical system error that requires immediate inspection.

A strong indication of an internal hardware fault occurs when the control unit becomes unresponsive via the OBD interface. Workshop diagnostic tools cannot establish a connection, making in-vehicle fault analysis impossible and pointing directly to a defective control unit.

If diagnostics are possible, specific fault codes are often retrieved. Entries such as “Internal Error” or manufacturer-specific DTCs indicating a defect within the control unit itself confirm the need for repair. Following an accident, the code “Crash Data Stored” provides definitive evidence that a reset is required.

In which vehicles is the K851M-EH100 control unit installed?

The Airbag Control Unit with part number K851M-EH100 is specifically designed for use in models manufactured by Infiniti. It is predominantly found in the M45 sedan of the Y50 series from the mid-2000s. At Airbag24, we offer professional repair services for this control unit.

At Airbag24, the K851M-EH100 control unit is repaired for the following models:

Infiniti M45 (Y50 series, circa 2005–2010)

Infiniti Premium M45

How is the K851M-EH100 repaired?

Repair at Airbag24 follows a standardized process: Upon receipt of the removed control unit, a comprehensive electronic analysis is conducted. Depending on the nature of the fault, crash data is either reset or repairs are performed at the component level. Finally, a functional test on the test bench ensures full operational readiness.

Once the control unit arrives at Airbag24, it undergoes a thorough incoming inspection. During this process, the fault memory is read out and the device’s communication is verified on a specialized test bench to pinpoint the exact cause of the fault.

If the defect is based on stored crash data, the internal memory chips (EEPROM/Flash) are read using specialized hardware. The crash-relevant data blocks are selectively erased and reset to factory settings, without altering vehicle-specific coding such as the VIN.

In cases of hardware failure, repairs are performed at the component level. Technicians replace defective parts like voltage regulators, transceivers, or damaged ICs, and rework solder joints when necessary. Following repair, the unit undergoes rigorous quality control and comprehensive functional testing. We provide a 12-month warranty on every repair.

What shipping options are available at Airbag24?

To send your control unit, you can opt for free self‑drop-off at a parcel shop or arrange a convenient UPS pickup at your preferred location. For return shipping, we offer free standard UPS delivery, faster UPS Express shipping, and cash-on-delivery options.

For sending your unit to us, you have two simple choices: either ship it to us yourself at no cost, or schedule a convenient UPS pickup directly from your home or workshop.

After successful repair, we provide several return‑shipping options:

Standard UPS shipping is free and typically takes 1–3 business days. If you need your part back sooner, choose UPS Express shipping, which usually takes 1–2 business days.

In addition, both Standard and Express UPS shipping are available with cash-on-delivery. Alternatively, you can also pick up your repaired control unit in person at our facility.