5 Causes Of An Airbag Light Coming On (and Minimum Deployment ...

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Seeing that airbag light illuminate in your dash can strike immediate fear to any driver. Will they fail do deploy when you need them most? Or will the airbags unexpectedly deploy while driving?

In many cases, a vehicle’s supplemental restraint system (SRS) light only signals a minor issue, even though we’ve been trained to equate any airbag problem with certain doom. Keep reading to learn the 5 most common reasons your airbag light comes on as well as the minimum speed needed for them to deploy.

Common Causes of the Airbag Light Coming On

1) Electrical Issues

The individual components of an airbag system are quite intricate. Problems with the airbag wiring harness, connections, couplers or power supply can disable airbags. Frayed, damaged, or loose wires create openings allowing shorts.

Intermittent warning lights point to wires or couplers vibrating free during driving. Check wire harnesses for damage. Bad grounds or voltage drops from aged car batteries also cause electrical trouble.

See Also: 5 Causes of the ‘Car With Lock Symbol” Light On

2) Seat Belt Issue

In some cases, not putting on your seat belt could cause the airbag light to come on. But there could be other seat belt issues that may cause this light to come on as well.

Perhaps your seat belt doesn’t snap securely into the buckle and stay in place. Maybe there is a problem with the sensors in the buckle and they don’t accurately tell the computer that you have fastened your seat belt.

Alternatively, there could be a problem with a seat belt pre-tensioner that may need to be repaired or replaced (especially if the vehicle’s been in a previous accident.

3) Damaged Sensors

It is possible to get into a small car accident (aka fender bender) that doesn’t deploy your airbags, but causes damage to at least one sensor. This typically occurs where the minimum speed for airbag deployment is not reached (see section below).

Crash sensors mounted in the front, side pillars, doors, and seats detect sudden deceleration signaling a collision. If damage or malfunctions occur, sensor trouble codes set off the warning light. Front sensor issues are most common, caused by hits to the bumper or wheel areas that jolt sensors.

4) Water Damage

If the internal components of your vehicle have water damage for whatever reason, then corrosion may form on the crash sensors of your airbag system.

This corrosion will distort their ability to function properly and it could result in the airbag light coming on.

5) Airbag System Not Reset

Once you’re in an accident which causes the airbags to deploy, simply replacing the airbag is not enough. Crash sensors, clock spring, seat belt pretensioners, and other SRS components must also be replaced. In addition, the airbag monitoring unit (the brains of the airbag system) will need to be reset or reprogrammed.

You will need to have a qualified mechanic or dealership reset/reprogram the SRS module so the airbag system can be used again. Alternatively, some companies allow you to ship them the airbag monitoring unit, they reset it for a fee, and then ship it back to you ready to install.

6) Blown Fuse

Each airbag component on the circuit gets power running through a specifically designated fuse. An overcurrent event from a short or spike in the system can blow this fuse cutting off power flow. Warning lights alert of lost power caused by a spent fuse needing replacement.

7) Defective SRS Module

As the brains of the airbag system, the SRS module constantly checks the status of components and sensors. If the module itself fails due to an internal error, water damage, or other cause, crash data inputs can fail to deploy airbags as needed.

In cases of a module malfunction, the airbag light may come on even when the rest of the system is completely functional.

See Also: Average Airbag Replacement Costs

Minimum Speed for Airbag Deployment

Airbags are designed for deployment when the front (or near front) of your vehicle collides with another vehicle or solid barrier. However, in order for the airbags to deploy, the minimum speed that you need to be driving during your collision is between 8 mph and 14 mph.

Most people are driving way above these speeds when they crash, usually between 35 mph and 60 mph. The faster you’re going during a collision, the more that you’ll need an airbag to save your life.

Diagnosing Airbag Issues

When the airbag warning light turns on, pinpointing the exact cause requires methodical diagnosis testing. Different options exist:

• OBDII Code Reader: The onboard diagnostics system stores trouble codes which point to certain components setting the light off, though codes do not always provide the full picture. Use an OBDII scan tool (with SRS capabilities) to access stored codes and then cross-reference with possible causes.
• Voltage Testing: An electrical system issue can disable airbags without setting codes. Test wiring harness, connectors, sensors and module voltage levels for drops showing breaks in power flow. This determines if replacement parts or wire repairs need addressing instead of just coded components.
• Visual Inspections: Damaged wiring harnesses, obviously disconnected sensors, corrosion in connectors can often be spotted through careful visual and physical checks before replacing correctly showing components. Look for points where electrical faults could occur like wear, crimps, or dirt buildup.

Without proper diagnostic testing, airbag repairs prove wasted if not addressing the root failure, exemplified by the light turning back on shortly after. Inspect stored codes but also follow through with thorough supplementary troubleshooting before assuming part replacements or resets.

Resetting the Airbag Light After Repairs

Once the underlying airbag system faults are successfully diagnosed and repaired/replaced, the airbag warning light needs to be reset to clear the trouble code memory and turn the light off.

Key Cycling

After completing repairs, turning the key into the “on” position for 30 seconds without cranking the engine allows the airbag diagnostic module to run through its self-check cycle. It resets status codes in the process.

Repeat this key on-off cycle procedure multiple times until the airbag warning light shuts off. Letting the vehicle sit for several minutes between cycles allows systems to power down completely each time.

Scan Tool Code Reset

The same OBD diagnostic scanners used to initially read stored trouble codes from airbag modules can also perform resets on most vehicles, turning the warning light off in the process.

This coded reset should only be done after correcting the flagged issues first or the trouble code(s) and subsequent airbag light will simply retrigger.

Manufacturer Specified Procedures

Some vehicle manufacturers designate their own specific steps for resetting airbag module warning lights separate from generic OBD scanners. Often part of an overall sensor or computer reset, this may entail intricate sequences of ignition or shift lever movements.

Always reference the exact make/model service manual for reset procedures before assuming only an OBD2 scan tool will work.

Verifying Light Stays Off

After performing resets using various methods, further road testing should follow. Drive the car through several full drive cycles allowing the airbag system’s self-diagnostics to run completely to check for fault code retriggers. Only if the dashboard warnings stay off continuously can the repair be verified as fully resolved.

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KevinKevin has been fascinated by anything automotive since his first go-kart as a kid to his time working as an auto tech for Dodge after obtaining his degree in automotive technology. When he's not working on cars or writing about them, you can find him and his E36 M3 at an event with the local chapter of the BMW CCA. Latest posts by Kevin (see all)

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