Why both lights are on at the same time

When your check engine light and Trac Off light illuminate together, they are usually connected to the same underlying problem. Trac Off (traction control off) typically activates when your vehicle's computer detects a fault in the engine, emissions system, or wheel speed sensors — the same systems that trigger the check engine light. The two lights appearing together is a signal that your vehicle's onboard diagnostic system has found an issue serious enough to disable traction control as a safety measure.

This is not the same as intentionally turning off traction control with a button. When both lights come on, your vehicle is doing it automatically because the computer cannot trust the sensor data it needs to manage traction safely. Driving with both lights on is generally safe for short distances to a repair shop, but you should not ignore the problem.

Key Takeaways

  • Both lights together usually mean a single fault in the engine, emissions, or wheel speed sensors — not two separate problems.
  • You can drive to a repair shop, but the issue should be diagnosed within a few days to avoid potential damage to the catalytic converter or transmission.
  • A diagnostic scan will read the specific fault code stored in your vehicle's computer and tell you exactly what failed.
  • Common causes include a faulty oxygen sensor, mass airflow sensor, wheel speed sensor, or loose gas cap — some fixable in minutes, others requiring parts replacement.
  • Do not ignore the lights if they stay on; traction control disabling itself is a warning that something is wrong with core vehicle systems.

What the diagnostic scan will show you

When you take your vehicle to a repair shop or auto parts store, a technician will connect a diagnostic scanner to the onboard diagnostic port (usually under the steering wheel on the driver's side). This scanner reads the fault code — a specific number that identifies which sensor or system failed. The code will be something like P0135 (oxygen sensor circuit) or P0101 (mass airflow sensor range), and it tells you exactly what to fix.

Many auto parts stores offer free diagnostic scans, though the quality varies. A shop scan is more thorough and will often include a printout of the code, what it means, and common causes. The code alone does not always tell you the exact part that failed — a P0135 code could mean a bad oxygen sensor, a wiring problem, or a connector issue — but it narrows the search dramatically and gives a repair shop a starting point.

Common causes of both lights together

The most frequent culprit is a faulty oxygen sensor. Your vehicle has at least two oxygen sensors (one before and one after the catalytic converter), and when one fails, the engine cannot adjust the fuel mixture correctly. This triggers the check engine light and, because the computer is running in a degraded state, it disables traction control as a precaution. Oxygen sensor replacement typically costs between $150 and $400 depending on which sensor and your vehicle model.

A loose or missing gas cap is the second most common cause and the easiest to fix. The cap seals the fuel system, and a loose cap allows fuel vapors to escape, which the emissions system detects. Tighten or replace the cap and clear the codes (or drive for a few cycles and the light may clear on its own). A new cap costs $5 to $20.

The mass airflow sensor measures how much air enters the engine so the computer can adjust fuel injection. When it fails or gets dirty, the engine runs poorly and both lights come on. Cleaning or replacing this sensor costs $150 to $400. A wheel speed sensor failure will also trigger both lights because the traction control system relies on wheel speed data; replacement usually runs $150 to $300 per wheel.

What to do before you go to the shop

Check your gas cap first. Unscrew it, inspect the rubber seal for cracks or debris, and screw it back on firmly. If it is cracked or the seal is damaged, buy a replacement at any gas station or auto parts store. Drive for 50 to 100 miles with the cap secured; if the lights were caused only by the cap, they should turn off on their own after the vehicle completes a full diagnostic cycle.

Do not attempt to clear the codes yourself using a scanner unless you plan to take the vehicle to a shop anyway. Clearing the codes without fixing the underlying problem means the lights will return within a few days or weeks, and you will have lost the diagnostic information that helps a technician pinpoint the issue. If you do clear the codes and the lights return, write down how many miles passed before they came back on — that information helps narrow down intermittent sensor problems.

When to drive to the shop versus calling a tow truck

Driving with both lights on is safe for short distances (under 20 miles) to a repair shop. Your vehicle will run, steer, and brake normally. Traction control being off means you will have less grip in slippery conditions, so avoid heavy rain, snow, or aggressive cornering. If you live more than 20 miles from a shop or the lights came on while you were already driving and the engine is running rough, hesitating, or stalling, call a tow truck instead.

Do not delay getting the vehicle scanned. Driving for weeks with both lights on can damage the catalytic converter (which costs $800 to $2,000 to replace) if the underlying problem is an oxygen sensor or fuel mixture issue. A diagnostic scan takes 30 minutes to an hour and costs $50 to $150; that investment now prevents a much larger repair bill later.

What happens after the repair

Once the repair is complete, the technician will clear the fault codes from the computer. The check engine light and Trac Off light should turn off when ready. If either light returns within a few days, the repair did not fully address the problem — this sometimes happens with intermittent sensor faults or if a connector was not fully seated. Return to the shop and ask them to re-scan the vehicle; most shops warranty their work for 30 days.

If the lights stay off, your vehicle is back to normal operation. Traction control will function again automatically. You do not need to do anything else unless the lights come on again in the future.

Frequently Asked Questions

Is it safe to drive with both lights on?

Yes, for short distances to a repair shop. Your engine, brakes, and steering work normally. Traction control being off means less grip in wet or icy conditions, so avoid aggressive driving. Do not drive more than 20 miles or delay getting a diagnostic scan.

Can I turn traction control back on myself?

No. When both lights are on, your vehicle's computer has disabled traction control automatically because it detected a fault. Pressing the traction control button will not override this; the system will not re-enable until the underlying problem is fixed and the codes are cleared.

Will the check engine light turn off on its own?

Only if the problem is temporary or intermittent. A loose gas cap might clear after a few drive cycles. Most other causes (sensor failure, wiring problems) require repair. The light will not turn off permanently until the fault is fixed.

How much will this cost to fix?

That depends on the fault code. A gas cap is $5 to $20. An oxygen sensor is $150 to $400. A mass airflow sensor is $150 to $400. A wheel speed sensor is $150 to $300. A diagnostic scan costs $50 to $150 and tells you exactly what needs repair.

What if I ignore the lights?

Your vehicle will continue to run, but you risk damage to the catalytic converter if the problem is fuel-related. Ignoring the lights for weeks or months can turn a $200 repair into a $1,500 one. Get a diagnostic scan within a few days.