Check Engine Light
A steady check engine light means the computer found an engine or emissions fault. A flashing light means an active misfire that can quickly damage the catalytic converter.
Can I drive it? Drive with care
Steady light: usually fine to drive short-term, get the code read soon. Flashing light: ease off the throttle and get the car checked right away.
Typical repair cost
Code reading is free at most auto-parts stores. A gas cap is $10-$25, an O2 sensor $150-$400, a catalytic converter $900-$2,500.
General US estimates, not quotes. Prices vary by region, vehicle and shop.
Symptoms to Look For
These signs indicate you might be experiencing this issue
- Orange engine icon illuminated on dashboard
- Possible rough running or stalling
- Reduced fuel economy
- Car may enter 'Limp Mode' (reduced power)
- Failed emissions test
Potential Causes
Most likely reasons for this problem, sorted by probability
Repair Solutions
Step-by-step instructions to diagnose and fix the problem
1Basic Troubleshooting
- 1
Check gas cap - tighten until clicks
- 2
Use OBD2 scanner to read trouble codes
- 3
Note codes (e.g., P0420, P0300, P0171)
- 4
Clear codes and see if they return
- 5
Check for loose vacuum hoses
2OBD2 Code Diagnosis
- 1
Plug scanner into OBD2 port under dashboard
- 2
Record all codes and freeze frame data
- 3
Research specific codes online or in service manual
- 4
Perform basic tests based on code (e.g., check sensor resistance)
- 5
Fix root cause before clearing codes
Need professional help?
Find a repair shop near you, or describe your exact symptoms to the AI mechanic
When to See a Mechanic
Do not wait if any of these apply
- The light is flashing
- The car runs rough, loses power or smells of fuel
- The light returns after the code was cleared
How to Prevent It
Simple habits that stop this problem coming back
- Tighten the gas cap until it clicks after every fill-up
- Follow the spark plug and air filter intervals in your manual
- Do not ignore a steady light: small faults become expensive ones
Frequently Asked Questions
Can I pass an emissions test with the light on?
No. In most US states a lit check engine light is an automatic fail.
Does disconnecting the battery clear it?
It resets the light but not the cause. The light and code return once the computer re-runs its tests.
Related Trouble Codes
Codes a scan tool may show with this problem
Related Issues
AI-generated and informational only. This is not a diagnosis of your specific vehicle and does not replace inspection by a qualified technician.