B1940 — Air Bag Crash Sensor #2 Ground Circuit Open

OBD2 code B1940 flags a problem with the airbag / restraint system (SRS) (B1940 — air bag crash sensor #2 ground circuit open: causes, symptoms & fix). Short, gentle driving to a shop is usually possible. Common culprits: failed clockspring (driver airbag circuit), damaged wiring under seats or in the steering column, SRS control module fault or stored crash data.

vehicle

Is it safe to drive?

Drive with caution The car drives normally, but with the SRS light on the airbags may not deploy in a crash. Treat it as a safety-critical repair: fine to drive to the shop, not fine to ignore for months.

How to diagnose with an OBD scanner

Read the code and freeze frame Connect an OBD2 scanner, confirm B1940 is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
Check for companion codes and TSBs Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many B0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
Inspect wiring and connectors Visually inspect the wiring harness and connectors related to the airbag / restraint system (SRS) for damage, corrosion, chafing or poor contact.
Subsystem check Read the SRS module with a scanner that supports airbag systems — generic OBD2 readers cannot see these codes.
Subsystem check Inspect under-seat connectors — they are often disturbed by seat movement or cleaning.
Verify the repair Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm B1940 does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for B1940 (parts and labor, USD, independent shop rates): Reconnect or repair SRS wiring/connectors: $80–$250; Replace a sensor or clockspring: $150–$500; SRS module reset or replacement: $300–$1,000. Overall, fixing B1940 usually costs between $80 and $1,000. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Common questions

What is the most common cause of B1940?

The most common causes are: failed clockspring (driver airbag circuit), damaged wiring under seats or in the steering column, SRS control module fault or stored crash data.

Is it safe to drive with B1940?

The car drives normally, but with the SRS light on the airbags may not deploy in a crash. Treat it as a safety-critical repair: fine to drive to the shop, not fine to ignore for months.

What are the symptoms of B1940?

Drivers most often notice: airbag (SRS) warning light on, no other driving symptoms, airbag system disabled message.

What does OBD2 code B1940 mean?

Will B1940 clear itself?

Sometimes B1940 clears after a few drive cycles if the fault was intermittent — for example a loose connector or a tank of bad fuel. The underlying cause usually remains, so the code tends to return. Clear it once; if it comes back, diagnose rather than erase it repeatedly.

B1940 — B1940 — Air Bag Crash Sensor #2 Ground Circuit Open: Causes, Symptoms & Fix

When a scan tool pulls code B1940, the vehicle's computer is reporting a specific electrical problem in the supplemental restraint system. B1940 indicates that the ground circuit for the second crash sensor in the airbag system has been interrupted — essentially, the sensor can no longer complete its ground connection. This falls within the B-series codes that cover body and chassis electrical systems, and it directly affects the safety equipment meant to protect occupants during a collision.

The SRS control module constantly watches the entire airbag circuit while the engine is running. It sends tiny test signals down each wire and expects specific responses back. When that ground path for crash sensor number two becomes open — broken or disconnected — the module detects the missing signal and logs B1940 once the fault persists long enough to clear any temporary electrical noise. At that moment, the module also captures freeze frame data, recording engine speed, load, temperature, and vehicle speed. That snapshot tells you exactly what conditions existed when the system lost contact with the sensor.

Most drivers notice only one thing: the airbag warning light glowing on the dash. Beyond that, the car feels and drives exactly as it should. That apparent normality is actually the concerning part — the system appears fine until it is needed. The module may also display a message indicating the airbag system is disabled, depending on the vehicle.

The reasons B1940 appears vary in frequency. Wiring problems sit at the top of the list — connectors under the seats or along the steering column suffer from constant flexing, cleaning, or simple wear. A failing clockspring in the steering column also ranks high, since it carries the driver's airbag circuit through the rotating column. Low system voltage or a depleted backup battery can mimic an open ground by starving the sensor of proper power. The SRS module itself may have failed or still hold crash data from a previous impact that was never cleared. A faulty impact or occupancy sensor, while less common, still triggers this code.

Symptoms

The airbag or SRS warning lamp stays illuminated after startup
No changes to steering, braking, acceleration, or any other driving function
A dashboard message stating the airbag system is disabled or inactive
In some vehicles, the seat belt pretensioners may also be deactivated
Occasionally, intermittent operation where the light flickers or goes out temporarily

Causes

Damaged, corroded, or loose wiring and connectors in the SRS harness, especially under the seats
Failed clockspring unit compromising the driver's airbag circuit
Depleted backup battery or chronically low system voltage affecting sensor operation
SRS control module fault or unrecovered crash data stored in module memory
Defective crash sensor number two or related impact/occupancy sensor
Poor ground connection at the sensor mounting point

How to Diagnose B1940

Start by connecting a scanner capable of reading SRS codes — a basic OBD2 reader will not access these modules. Confirm B1940 is stored, then save the freeze frame data before anything else. That recorded information reveals the engine conditions when the fault first appeared and guides your next steps.

Next, pull any related codes. Often B1940 arrives alongside other crash sensor or airbag circuit codes that point directly to the failed component. Check manufacturer TSB databases for your specific make and model; many B-series code patterns have documented factory fixes or software updates that a dealer can apply.

Visually inspect the SRS wiring harness. Focus on the areas most prone to movement: under both front seats, inside the steering column covers, and at each sensor connector. Look for broken insulation, bent pins, moisture intrusion, or loose plugs that work free over time.

If the harness looks intact, test the specific crash sensor referenced by B1940. Measure its ground circuit resistance with a multimeter and compare against manufacturer specifications. A reading above specification or infinite ohms confirms an open ground path.

Clear the code after any repairs, then complete a full drive cycle — especially under conditions similar to those captured in the freeze frame — to verify the light does not return.

Repair Options and Costs

Not every B1940 repair requires a expensive parts swap. Technicians work through the system from simplest to most involved:

Repair or reconnect loose, damaged, or corroded SRS wiring and connectors: $80–$250
Replace a failed clockspring or crash sensor: $150–$500
SRS control module reset or full replacement with reprogramming: $300–$1,000

Labor rates at independent shops typically run $80–$120 per hour. Wiring repairs and connector cleaning usually fall on the lower end of that range. Clockspring replacement requires steering column disassembly, pushing costs toward the middle. Module replacement involves parts, programming, and sometimes manufacturer-specific tools.

Total Cost Summary

Expect to spend between $80 and $1,000 to resolve B1940, depending entirely on which component actually failed. The most common repairs — wiring and connectors — land at the bottom of that range. Diagnosing the fault correctly before purchasing parts is the single best way to keep costs down. Never assume the module is the culprit; spend an hour checking the harness first.

Can You Drive with B1940?

The vehicle handles, stops, and steers normally. However, the airbag system will not deploy in a collision while the warning light is on. That means you lose a critical layer of protection for both the driver and passengers. It is safe to drive directly to a repair facility, but leaving B1940 unresolved for weeks or months is not advisable. Treat it as a safety-critical issue and schedule service promptly.