B101D: Internal Module Hardware Fault

Hardware fault

What B101D means

Every time the ignition comes on, the restraint control module runs through a self test. It verifies its memory, its internal power supplies, and the circuits it uses to fire an inflator. B101D is what gets written when one of those internal checks does not pass, and the module disables deployment until the fault clears.

This code is different from the circuit codes that name a specific airbag or belt. There is no connector to reseat and no loop to measure, because the failure is on the board inside the module housing. A shop can test the harness all day and find nothing wrong with it.

Common causes

• Age related failure of a component on the module's internal board
• Moisture that reached the module, often from a wet carpet or a leaking windshield
• A voltage event from jump starting, a failing alternator, or welding on the vehicle
• Physical damage to the module housing or its mounting during a repair
• A module that was previously deployed and then cleared improperly by a third party tool

Crash data or hardware fault?

Hardware means the module itself is at fault, which is a separate thing from stored crash data. Crash data is a permanent record of a deployment and cannot be erased with a scan tool. B101D is an internal condition the module is reporting on its own behalf, and depending on the failure it may be stored rather than continuously present.

Does our reset clear it?

This is the code where our mail-in service is most often the answer. When B101D is stored and the module has no live circuit faults, resetting the unit back to a factory ready state clears the internal fault memory and puts the module back in service. If the board has genuinely failed and the fault is live, no reset fixes it and the module needs to be replaced.

Which makes throw it

Cadillac and GMC both use B101D with this meaning, which puts it across a range of GM cars and trucks sharing the same restraint module family.

What to do next

Before assuming the module is bad, check battery voltage and the module's power and ground circuits, since a module starved of clean voltage can fail its own self test. Look for water under the carpet near the module mount as well. Once the vehicle side checks out, mail the module to us and we will reset it, or call 501-988-0611 if you would rather ask first. Related codes: B1019, B1327, B0091.