Discover how to fix check engine and traction light on with simple diagnostic steps and practical solutions. This guide walks you through identifying causes, using an OBD2 scanner, and safely resetting warning lights—no mechanic required.
Key Takeaways
- Check engine and traction lights often share the same root cause: a problem with the vehicle’s engine or emissions system can trigger both warnings.
- Use an OBD2 scanner to read diagnostic trouble codes (DTCs): this is the fastest way to pinpoint what’s causing the lights to come on.
- Common culprits include faulty oxygen sensors, loose gas caps, or wheel speed sensor issues: these are often easy and inexpensive to fix.
- Never ignore both lights coming on together: this could indicate a serious drivetrain or stability control issue that affects safety.
- Reset the lights only after fixing the underlying problem: clearing codes without repairs will cause the lights to return.
- Regular maintenance prevents future warning lights: keep up with oil changes, tire pressure, and sensor inspections.
- If unsure, consult a professional mechanic: some issues require specialized tools or expertise to resolve safely.
How to Fix Check Engine and Traction Light On
Seeing both the check engine light and traction control light illuminate on your dashboard can be alarming. You might wonder: Is my car safe to drive? What’s wrong? Do I need to tow it to a shop right away? The good news is that in many cases, these warning lights can be diagnosed and fixed at home with the right tools and a bit of know-how.
In this comprehensive guide, you’ll learn exactly how to fix check engine and traction light on—step by step. We’ll cover what these lights mean when they appear together, how to use an OBD2 scanner to read error codes, common causes, DIY fixes, and when it’s time to call a professional. By the end, you’ll have the confidence to tackle this issue safely and save money on unnecessary repairs.
Understanding the Check Engine and Traction Control Lights
Before diving into fixes, it’s important to understand what each light represents and why they might come on simultaneously.
Visual guide about How to Fix Check Engine and Traction Light On
Image source: i.redd.it
What Does the Check Engine Light Mean?
The check engine light—also known as the malfunction indicator lamp (MIL)—is part of your vehicle’s onboard diagnostics system (OBD2). It lights up when the engine control unit (ECU) detects a problem with the engine, emissions system, or related components. This could range from something minor like a loose gas cap to more serious issues like a failing catalytic converter.
What Does the Traction Control Light Mean?
The traction control system (TCS) helps prevent wheel spin during acceleration, especially on slippery roads. The traction control light usually flashes when the system is actively working. But if it stays on solid, it means the system has been disabled or there’s a fault. This often happens when the vehicle detects inconsistent wheel speed data—usually from a faulty wheel speed sensor or ABS issue.
Why Do Both Lights Come On Together?
When both the check engine and traction control lights are on, it’s often because they’re connected through the vehicle’s computer systems. For example:
- A faulty oxygen sensor can trigger the check engine light and also affect engine performance, which in turn disables traction control.
- A problem with the ABS module or wheel speed sensors can disable traction control and also send error codes that trigger the check engine light.
- Low engine power or misfires can cause the ECU to shut down non-essential systems like traction control for safety.
In short, these systems are interlinked. Fixing the root cause of one often resolves the other.
Step 1: Stay Calm and Assess the Situation
First things first—don’t panic. While warning lights should never be ignored, they don’t always mean your car is about to break down. Here’s what to do right away:
Check for Immediate Danger
Ask yourself:
- Is the car running roughly or stalling?
- Is there a burning smell, smoke, or unusual noise?
- Is the vehicle pulling to one side or feeling unstable?
If you answer “yes” to any of these, pull over safely and turn off the engine. Call a tow truck if needed. Driving with serious mechanical issues can cause more damage or become a safety hazard.
Note the Behavior of the Lights
Observe whether the lights are:
- Solid: Usually indicates a less urgent issue.
- Flashing: Often means a severe problem like a misfire that could damage the catalytic converter. Stop driving immediately.
If both lights are solid and the car is running smoothly, you likely have time to diagnose the issue at home.
Step 2: Use an OBD2 Scanner to Read the Codes
The most effective way to fix check engine and traction light on is to find out exactly what’s wrong. That’s where an OBD2 scanner comes in.
What Is an OBD2 Scanner?
An OBD2 (On-Board Diagnostics II) scanner is a handheld device that plugs into your car’s diagnostic port and reads error codes stored in the ECU. These codes—called Diagnostic Trouble Codes (DTCs)—tell you which system or component is malfunctioning.
Where Is the OBD2 Port?
The OBD2 port is usually located under the dashboard on the driver’s side. Look for a 16-pin connector near the steering column, often behind a small panel or cover. In most cars, it’s within arm’s reach when you’re sitting in the driver’s seat.
How to Use the Scanner
- Turn off the engine.
- Plug the scanner into the OBD2 port.
- Turn the ignition to the “ON” position (but don’t start the engine).
- Follow the scanner’s instructions to read codes. Most scanners have a “Scan” or “Read” button.
- Write down all the codes displayed. They usually look like P0xxx (e.g., P0420, P0171).
Interpreting the Codes
Once you have the codes, use the scanner’s built-in database or search online to understand what they mean. For example:
- P0420: Catalyst system efficiency below threshold (often a bad catalytic converter or oxygen sensor).
- P0171: System too lean (bank 1)—could be a vacuum leak or faulty MAF sensor.
- C0035: Right front wheel speed sensor circuit malfunction—common cause of traction light.
Some scanners also provide plain-English descriptions, making it easier for beginners.
Pro Tip: Use a Free App with a Bluetooth Scanner
If you don’t want to buy a standalone scanner, consider a Bluetooth OBD2 adapter (like the popular ELM327) paired with a free app such as Torque Pro (Android) or OBD Fusion (iOS). These let you read codes and monitor live data right on your phone.
Step 3: Address Common Causes
Now that you have the codes, it’s time to fix the problem. Below are the most common causes of both check engine and traction lights coming on—and how to resolve them.
1. Loose or Faulty Gas Cap
Symptoms: Check engine light on, possibly with code P0455 (large EVAP leak) or P0457 (loose cap).
Why it matters: The gas cap seals the fuel system. If it’s loose, cracked, or missing, fuel vapors can escape, triggering the check engine light. In some vehicles, this can also affect engine performance and indirectly disable traction control.
How to fix:
- Turn off the engine.
- Remove the gas cap and inspect it for cracks or wear.
- Reinstall it firmly—you should hear it click 3–5 times.
- Drive for 50–100 miles. The light may turn off on its own.
- If not, use the scanner to clear the code.
Cost: $10–$20 for a new cap if needed.
2. Faulty Oxygen (O2) Sensor
Symptoms: Check engine light with codes like P0135, P0141, or P0420. Poor fuel economy, rough idle.
Why it matters: O2 sensors monitor exhaust gases and help the ECU adjust the air-fuel mixture. A bad sensor can cause the engine to run rich or lean, triggering the check engine light and reducing power—which may disable traction control.
How to fix:
- Locate the faulty sensor using the code (e.g., Bank 1 Sensor 1 = front sensor on cylinder 1 side).
- Use an O2 sensor socket and wrench to remove it.
- Install a new sensor (available at auto parts stores).
- Clear the code with the scanner.
Cost: $20–$100 per sensor, depending on the vehicle.
3. Wheel Speed Sensor or ABS Issue
Symptoms: Traction control light on, possibly with ABS light. Codes like C0035, C0040, or U0121.
Why it matters: Wheel speed sensors tell the ABS and traction control systems how fast each wheel is spinning. If one fails, the system can’t detect wheel slip, so traction control shuts off. This can also trigger a check engine light in some vehicles.
How to fix:
- Identify the faulty sensor from the code (e.g., right front).
- Locate the sensor near the wheel hub.
- Disconnect the electrical connector.
- Remove the sensor (may require removing the wheel or brake components).
- Install the new sensor and reconnect the wiring.
- Clear codes and test drive.
Cost: $30–$80 per sensor.
4. Mass Airflow (MAF) Sensor Problems
Symptoms: Check engine light with codes P0101, P0102, or P0171. Hesitation, poor acceleration.
Why it matters: The MAF sensor measures how much air enters the engine. If it’s dirty or faulty, the ECU can’t calculate the correct fuel mixture, leading to performance issues that may affect traction control.
How to fix:
- Locate the MAF sensor (usually between the air filter and throttle body).
- Unplug the electrical connector.
- Remove the sensor.
- Clean it with MAF sensor cleaner (do not use compressed air or regular cleaners).
- Reinstall and clear codes.
- If cleaning doesn’t work, replace the sensor.
Cost: $10 for cleaner; $50–$200 for a new sensor.
5. Catalytic Converter Failure
Symptoms: Check engine light with code P0420 or P0430. Reduced power, sulfur smell, rattling noise.
Why it matters: A failing catalytic converter can restrict exhaust flow, reducing engine performance and triggering the check engine light. In some cases, this can also disable traction control due to low engine power.
How to fix:
- This is a more complex repair. First, rule out other causes (like O2 sensors).
- Use a backpressure test or infrared thermometer to check converter efficiency.
- If confirmed faulty, replacement is required—usually by a mechanic.
Cost: $500–$2,000, depending on the vehicle.
Step 4: Clear the Codes and Test Drive
After fixing the issue, it’s time to reset the warning lights.
How to Clear the Codes
- Plug the OBD2 scanner back in.
- Turn the ignition to “ON.”
- Select “Clear Codes” or “Erase DTCs” on the scanner.
- Confirm the action.
- Turn off the ignition and unplug the scanner.
Test Drive the Vehicle
Drive the car for 20–30 minutes, including highway speeds if possible. This allows the ECU to relearn and monitor systems. If the lights stay off, the problem is likely resolved.
Note: Some codes may take a few drive cycles to clear completely. Don’t worry if the light doesn’t turn off immediately—just keep driving normally.
Step 5: Prevent Future Warning Lights
Now that you’ve fixed check engine and traction light on, take steps to avoid recurrence.
Regular Maintenance
- Change the oil and filter every 5,000–7,500 miles.
- Replace air and fuel filters as recommended.
- Inspect spark plugs and ignition coils.
- Check tire pressure monthly.
Inspect Sensors and Wiring
Periodically check O2 sensors, MAF sensor, and wheel speed sensors for dirt, damage, or loose connections. Clean or tighten as needed.
Use Quality Fuel and Parts
Cheap fuel or low-quality replacement parts can cause sensor errors and performance issues. Stick to reputable brands.
Monitor Your Dashboard
Pay attention to new warning lights or changes in driving behavior. Early detection saves money and prevents breakdowns.
Troubleshooting: What If the Lights Come Back On?
Sometimes, the lights return after clearing. Here’s what to do:
Recheck the Codes
Use the scanner again. The same code? The fix may not have been complete. A different code? You may have multiple issues.
Inspect Your Work
Did you install the part correctly? Is the wiring secure? A loose connection can cause intermittent faults.
Consider Professional Help
If you’ve tried everything and the lights keep coming back, it’s time to visit a trusted mechanic. Some problems—like internal engine damage or complex electrical faults—require advanced diagnostics.
When to Call a Mechanic
While many issues can be fixed at home, some situations require professional help:
- The check engine light is flashing.
- You smell burning, see smoke, or hear loud noises.
- The car is stalling or losing power.
- You’re unsure about the repair or lack the tools.
- The same code keeps returning after replacement.
A certified mechanic has access to advanced tools and can perform tests like smoke testing for vacuum leaks or oscilloscope analysis for sensor signals.
Conclusion
Fixing check engine and traction light on doesn’t have to be scary or expensive. With the right approach—starting with an OBD2 scan—you can identify the root cause, apply a targeted fix, and get back on the road safely. Remember: these lights are your car’s way of saying, “Hey, something’s not right.” Listen to it, but don’t panic.
By following this guide, you’ve learned how to diagnose common issues, perform DIY repairs, and know when to seek help. Keep your scanner handy, stay on top of maintenance, and you’ll minimize the chances of seeing those dreaded dashboard lights again.
Now go enjoy the drive—confidently.