Cause
Open circuit in the airbag deployment loop
The circuit that would fire an airbag, pretensioner or load limiter is broken somewhere between the restraints module and the device.
A deployment loop is not an ordinary circuit and the module does not test it in an ordinary way. The device contains an initiator — a squib — with a precise, known resistance, and the module measures that resistance continuously. That lets it tell an intact device from a broken circuit without ever firing anything, which is the only safe way to check a one-shot explosive.
An open loop means the device cannot fire. And because a restraints module that cannot verify one loop will usually not authorise any deployment — firing some devices and not others can be worse than firing none — a single open circuit commonly disables the entire restraint system. The car drives perfectly and is far less able to protect anyone in it.
Where the break is depends on which device, and the pattern is worth knowing. For the driver airbag it is most often the clockspring, the coiled ribbon cable that carries the circuit into a steering wheel that rotates. For anything in a seat it is the harness beneath it, which flexes on every adjustment and is routinely damaged by objects pushed underneath or by seats being removed. For side and curtain devices it is usually a connector in the pillar or sill.
Never test a deployment loop with an ordinary multimeter. The current a meter passes to measure resistance can be enough to initiate a squib. This is what dedicated restraint-system equipment and the documented disable procedure exist for.
Typically specialist work. Needs equipment or training most home workshops do not have.
Codes this can cause (65)
Codes where this is a likely explanation first, rather than merely a possible one.
- B0001 Driver Frontal Stage 1 Deployment Control Likely for this code High
- B0002 Driver Frontal Stage 2 Deployment Control Likely for this code High
- B0003 Driver Frontal Stage 3 Deployment Control Likely for this code High
- B0004 Driver Knee Bolster Deployment Control Likely for this code High
- B0005 Collapsible Steering Column Deployment Control Likely for this code High
- B0010 Passenger Frontal Stage 1 Deployment Control Likely for this code High
- B0011 Passenger Frontal Stage 2 Deployment Control Likely for this code High
- B0012 Passenger Frontal Stage 3 Deployment Control Likely for this code High
- B0013 Passenger Knee Bolster Deployment Control Likely for this code High
- B0020 Left Side Airbag Deployment Control Likely for this code High
- B0021 Left Curtain Deployment Control 1 Likely for this code High
- B0022 Left Curtain Deployment Control 2 Likely for this code High
- B0028 Right Side Airbag Deployment Control Likely for this code High
- B0029 Right Curtain Deployment Control 1 Likely for this code High
- B002A Right Curtain Deployment Control 2 Likely for this code High
- B0030 Second Row Left Side Airbag Deployment Control Likely for this code High
- B0031 Second Row Left Frontal Stage 1 Deployment Control Likely for this code High
- B0032 Second Row Left Frontal Stage 2 Deployment Control Likely for this code High
- B0033 Second Row Left Frontal Stage 3 Deployment Control Likely for this code High
- B0038 Second Row Right Side Airbag Deployment Control Likely for this code High
- B0039 Second Row Right Frontal Stage 1 Deployment Control Likely for this code High
- B003A Second Row Right Frontal Stage 2 Deployment Control Likely for this code High
- B003B Second Row Right Frontal Stage 3 Deployment Control Likely for this code High
- B0040 Third Row Left Side Airbag Deployment Control Likely for this code High
- B0041 Third Row Left Frontal Stage 1 Deployment Control Likely for this code High
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Others who found this
Be the first to write this up
Nothing posted about this yet. Whatever you found is worth writing down — even a dead end saves someone the same afternoon.
What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
Sign in or create an account to add what you found about Open circuit in the airbag deployment loop.