Airbag warning lamp on, or airbag missing

What causes it

• A chafed or broken wire in the loom under a front seat, which is the single most common cause and is often triggered by sliding the seat or fitting seat covers
• A worn clockspring behind the steering wheel, which carries the driver's airbag circuit through the rotating column
• A crash pre-tensioner or airbag that has deployed and never been replaced, or a module with a stored crash record
• Low battery voltage or a flat-battery event leaving a fault code, plus corroded connectors on cars that have had damp footwells

Advisory or failure?

An SRS malfunction indicator lamp that is indicating a system malfunction is a major defect, and so is an airbag fitted as original equipment that is obviously missing or obviously inoperative. Seat belt pre-tensioners and load limiters fitted from the factory are treated the same way: obviously missing or deployed is a major defect. There is no advisory or dangerous grading anywhere in this part of the test. Two distinctions matter. A lamp that is lit only to show the passenger airbag has been switched off or has automatically disarmed is not a defect, and testers are told not to fail it. And the check is on the malfunction lamp itself — where no lamp is fitted, or the bulb no longer illuminates at all, it cannot indicate a fault and so cannot be failed, though a warning message on a dashboard display can be used as supporting evidence that a genuine malfunction exists. Removing the bulb to hide a fault is a well-known trick and testers know to look for a lamp that never lights during the ignition self-check.

Can you fix it yourself?

Garage job

Reading the code is the only sensible first step and a generic scanner will often not do it, because airbag faults sit on a separate module that many cheap tools cannot reach. Beyond diagnosis this is a system with pyrotechnic charges in it: an airbag can deploy while you handle it, and the manufacturer's procedure — battery disconnected, a stated wait for the capacitors to discharge, connectors handled in the right order — exists for good reason. Never probe an airbag circuit with a multimeter. The one honest DIY task is the common one: with the battery off, inspect the loom under each front seat for a wire that has been pinched or stretched by the seat runner, which is often the whole fault. Clearing the code without fixing the cause simply brings the lamp back, and a system with a stored crash record needs the module replaced or reset properly.

What it costs

Diagnosis is £50 to £90 at most independents and is the necessary first spend, since the fault code determines everything. From there the spread is wide. A repaired or replaced seat loom is £120 to £250 fitted, a clockspring £80 to £200 depending on the car, and a corroded connector or earth is often an hour of labour and no parts. A replacement airbag module, or an airbag unit itself, is where the top of the band goes and beyond — original parts only, coded to the vehicle, and some are supply-restricted. A car being sold with an unresolved airbag light will lose more in negotiation than the repair would have cost.

What happens if you ignore it

A lit lamp means the system has taken itself out of service, so the airbags and pre-tensioners will very likely do nothing in a collision. That is a serious loss on a modern car, because the belt and the bag are designed to work together — the belt alone is not the whole restraint. There is also a resale and insurance dimension: an unexplained airbag fault suggests undisclosed accident damage, and buyers walk away from it. Nothing about the fault gets cheaper by waiting, and a chafed seat loom left alone can eventually set off the very device it is wired to.

Common questions

Does an airbag warning light fail the MOT?

Yes. An airbag or SRS malfunction indicator lamp that is indicating a system fault is a major defect and a failure. An airbag fitted as original equipment that is obviously missing or inoperative is also a major defect, and so are factory-fitted seat belt pre-tensioners that are missing or already deployed. There is no advisory grading anywhere in this part of the test.

Will my airbags still work with the warning light on?

Assume not. A lit lamp means the restraint system has detected a fault and taken itself out of service, so the airbags and pre-tensioners will very likely do nothing in a collision. On a modern car the belt and the bag are designed to work together, so the belt on its own is not the whole restraint.

Can I turn the airbag warning light off myself?

Clearing the code without fixing the cause simply brings the lamp back, and removing the warning bulb to hide a fault is a well-known trick that testers watch for during the ignition self-check. Reading the code needs a scanner that can reach the airbag module, which many cheap tools cannot. Never probe an airbag circuit with a multimeter.

Is the passenger airbag off light an MOT failure?

No. A lamp lit only to show that the passenger airbag has been switched off, or has automatically disarmed, is not a defect and testers are told not to fail it. What fails is the malfunction indicator reporting a genuine system fault, which is a different lamp with a different meaning.

How much does it cost to fix an airbag warning light?

Diagnosis is £50 to £90 and is the necessary first spend, because the fault code determines everything else. A chafed loom under a front seat, which is the most common cause, is £120 to £250 repaired or replaced, and a clockspring £80 to £200. A replacement airbag or control module is the expensive end, at original-equipment prices and coded to the vehicle.

Cars this happens to most

Of every model with at least 2,000 tests in the DVSA data, these record airbag warning lamp on, or airbag missing on the largest share of their MOTs. Across all of them the typical rate is 0.6% of tests.

1. Hyundai Matrix4.1%

   115 times in 2,809 tests

2. Ssangyong Rodius3.4%

   89 times in 2,620 tests

3. Nissan Almera3.3%

   375 times in 11,249 tests

4. Rover 753.2%

   198 times in 6,210 tests

5. BMW Z32.9%

   320 times in 11,194 tests

6. Nissan Primera2.7%

   66 times in 2,490 tests

7. Isuzu Rodeo2.4%

   100 times in 4,178 tests

8. MG GS2.4%

   68 times in 2,849 tests

A high rate here is a property of the fleet as much as the car: these models skew old, and almost everything fails more with age. It is a reason to check the item on a used example, not proof the model is badly built. Models with fewer than 2,000 tests are left out because a rate drawn from a few hundred cars moves too much to rank.

Pass rates for every make and model →

Warning lights behind this

This defect is what a tester writes down. What you see from the driver’s seat is a symbol, and it is worth checking which one, because manufacturers reuse the same shape for more than one system.

• Airbag warning lightWhat it means and whether you can keep driving
• Passenger airbag off lightWhat it means and whether you can keep driving

Fault codes behind this failure

A failure certificate records that the lamp was lit, not what lit it. If this is what your certificate says, one of these codes is usually stored behind it, and reading it is the difference between a diagnosis and a guess.

• B0001 Driver's airbag circuit fault
• B0010 Passenger's airbag circuit fault
• B0020 Left side airbag circuit fault
• B0081 Front passenger seat belt buckle switch fault
• B0092 Front left side impact sensor fault
• U0001 The car's main communication network has failed
• U0126 No communication with the steering angle sensor
• U0155 No communication with the instrument cluster

Other common defects

• Direction indicator not working
• Stop lamp not working
• Lamp of the wrong colour, position or intensity
• Brake pipe corroded
• See all defects →