What causes check engine light and traction control light on?

When both lights illuminate, it usually means the vehicle’s computer has detected a fault that could affect the engine, emissions, or stability systems. In many cases, a simple issue like a loose gas cap triggers the check engine light, while the traction control light signals a problem with wheel speed sensors, ABS, or stability control. A professional diagnostic using an OBD-II scanner is typically needed to pinpoint the exact cause.

What the lights indicate

The check engine light (CEL) signals a fault detected by the engine control unit related to emissions or engine operation. The traction control light (often labeled TC or ESC) indicates a problem with the traction/stability system or that the system is actively intervening to maintain grip. When both lights appear, there may be multiple faults or a shared cause such as a sensor or ABS module affecting more than one subsystem.

Common causes of the check engine light

Below are frequent reasons the CEL may illuminate, spanning inexpensive fixes to more serious mechanical or sensor problems.

• Loose or faulty gas cap


• Oxygen sensor failure or improper readings


• Mass air flow (MAF) sensor contamination or failure


• Faulty spark plugs or ignition coils


• Catalytic converter efficiency issues


• Vacuum leaks or intake manifold leaks


• EVAP system faults (fuel vapor system)


• Faulty fuel injector or fuel delivery issues


• Crankshaft or camshaft position sensor problems


• Wiring or connector problems in the engine bay

In many cases, addressing the simplest causes first (like tightening the gas cap) can clear the light, but persistent or complex faults require a diagnostic scan and repair.

Common causes of the traction control light

Below is a list of typical reasons the traction control or stability control light may come on, indicating issues with how the car manages wheel grip and braking.

• Faulty wheel speed sensor or damaged wiring


• ABS system fault or sensor problem


• Low brake fluid or worn brake components


• Faulty steering angle sensor or ESC/ESP fault


• Malfunctioning traction control module or software


• Electrical faults such as blown fuses or damaged grounds


• Intermittent faults from engine control or transmission control modules

Traction control failures can disable or limit stability assistance, so a persistent light should be checked promptly, especially in poor driving conditions.

What to do next

If either light stays on continually, start with a diagnostic check to read the stored trouble codes. The following steps help guide the process:

• Have the vehicle scanned with an OBD-II tool to identify the exact codes and their freeze-frame data.


• Check for simple fixes first, such as ensuring the gas cap is tight and inspecting for obvious vacuum leaks or damaged wiring.


• Inspect braking system components (brake fluid level, pads, rotors) if the traction control light relates to ABS or brakes.


• Address any codes related to misfires or sensor faults promptly to avoid further damage.


• Drive conservatively if a code suggests misfire or loss of power; if the CEL is flashing, pull over safely and seek immediate service.

Note: Some issues require professional diagnosis and repair, and attempting risky repairs yourself can worsen problems or affect emissions compliance and safety systems.

Summary

In short, the check engine light points to engine or emissions faults detectable by the ECU, while the traction control light points to issues with wheel speed sensing, braking, and stability systems. Common causes range from simple fixes like a loose gas cap to more complex sensor, wiring, or module faults. A diagnostic scan is the most reliable way to identify the exact cause, followed by appropriate repair or replacement. Addressing these lights promptly helps protect engine performance, fuel efficiency, and vehicle safety in varying driving conditions.

Why would my traction control and check engine light come on?

Traction control and check engine lights can be caused by a number of things, including low tire pressure, faulty sensors, or a problem with the truck's computer system. Have you checked the tire pressure and made sure all the sensors are working properly?

Why did my check engine light and trac off light come on at the same time?

The most likely reason the check engine light and trac off light illuminate at the same time is that a problem detected by the engine control system triggers the automatic shutdown of the traction control system. Common causes include faulty sensors, such as a wheel speed sensor or a mass air flow sensor, as well as issues like engine misfires or a loose gas cap. To find the exact cause, you need to have the diagnostic trouble codes (DTCs) read from the vehicle's computer using an OBD2 scanner.
 
Common causes

• Faulty sensors: A bad wheel speed sensor is a very common cause because it provides data to both the traction control and anti-lock brake (ABS) systems. Other sensors like a mass air flow (MAF) or oxygen (O2) sensor can also cause this. 
• Engine misfires: If the engine is misfiring, it can cause enough instability that the system disables traction control, and it will also trigger the check engine light. 
• Loose or damaged gas cap: A loose or faulty gas cap can create an EVAP system leak, triggering the check engine light. Because of the system's interconnectedness, this can also turn on the traction control light. 
• Cooling system issues: A significant coolant leak can lead to engine overheating, which may activate both lights. 
• Other issues: Problems with the throttle body, alternator, or other engine components can also cause these lights to come on simultaneously. 

What to do

1. Check the gas cap: A simple first step is to ensure your gas cap is on tightly. 
2. Get the codes read: The most important step is to use an OBD2 scanner to read the diagnostic trouble codes (DTCs) from your car's computer. 
3. Inspect components: Once you have the codes, inspect the related components, such as wheel speed sensors or MAF sensors, for any visible damage or dirt. 
4. Address the root cause: The traction control light is often a symptom of the engine problem, so fixing the underlying issue will likely resolve both lights. 

Important note

• The "TRAC OFF" light means the traction control system is off. While you can still drive, you will not have the benefits of this system. 
• The "Check Engine" light can be solid or flashing. A flashing light indicates a more serious engine problem, such as a severe misfire, that requires immediate attention. 

How much does it cost to fix traction control?

Fixing traction control can cost anywhere from $100 to over $1,300, depending on the problem. A simple issue like a faulty wheel speed sensor might cost $100–$300, while a more complex replacement of a brake or ABS module could be $1,000 or more. The final price depends on the specific vehicle, the part needed, and the labor involved. 
Common repairs and their estimated costs

• Wheel speed sensor replacement: The most frequent cause is a faulty wheel speed sensor. 
  • Cost: ~$100–$300, including parts and labor. 
  • Factors: Price can vary based on vehicle, labor time, and part accessibility. 
• Brake module or ABS module replacement: A major component like the brake module or ABS module is a more expensive fix. 
  • Cost: ~$300 to over $1,300. 
  • Factors: The cost depends on the vehicle's make and model. 
• Software updates: In some cases, the issue can be resolved with a software update, which may be covered under warranty or warranty enhancements. 
• Alignment issues: Sometimes, an alignment problem can trigger the light. 
  • Cost: Varies, but an alignment itself is often in the range of $80–$200. 
  • Factors: If a part like a control arm is bent, the cost can increase significantly. 

How to get a more accurate estimate

• Get a diagnostic check: A professional mechanic can perform a diagnostic scan to pinpoint the exact cause of the problem. 
• Provide vehicle details: When asking for a quote, be sure to provide your vehicle's make, model, and year, as this can significantly affect the price. 

Is it safe to drive with the traction control and service engine light on?

It is not recommended to drive with both the engine light and traction control light on, especially if the engine light is flashing. You may be able to drive short distances if the engine light is steady and the car is not shaking, but you should get it inspected and repaired as soon as possible to prevent further damage and ensure safety. 
What to do if both lights are on

• Assess the severity:
  • Flashing engine light: This indicates a serious engine misfire and you should pull over immediately and have the vehicle towed. 
  • Steady engine light: If the light is steady and the car is not shaking or making strange noises, you can likely drive to a mechanic, but do so promptly. 
• Check for simple fixes:
  • Check your gas cap to ensure it's on tightly, as a loose cap can sometimes trigger the engine light. 
  • If your ABS light and brake warning light are also on, it could be a braking system issue, and driving may be unsafe. 
• Drive with caution:
  • If you must drive, do so carefully and be prepared to stop. The traction control system may not be working, which could affect your ability to maintain traction on slippery roads. 
• Seek professional help:
  • Get the trouble codes scanned by a mechanic to diagnose the specific problem. It's likely there's a shared issue, such as a faulty sensor, that is causing both lights to come on.