What Does Check Engine Light Mean?
Reviewed by automotive technicians · Last updated August 22, 2026
Quick Answer
Check Engine Light = The ECM has detected a fault affecting emissions, fuel economy, or engine operation. On Audi models, common causes include the secondary air injection system, oxygen sensor failure, or turbocharger boost pressure issues.
Severity: Warning · System: Audi A4 (2017-2025)
DRIVE WITH CAUTION — Repair Soon
The ECM has detected a fault affecting emissions, fuel economy, or engine operation. On Audi models, common causes include the secondary air injection system, oxygen sensor failure, or turbocharger boost pressure issues.
What you see: A yellow/orange engine-shaped icon on the instrument cluster. May be solid or flashing.
What to Do Right Now
Check if the light is solid or flashing. If solid and the car drives normally, schedule a diagnostic scan within a few days. If flashing, pull over immediately — this indicates an active misfire that can destroy the catalytic converter. Audi's direct injection engines are particularly sensitive to carbon buildup, which can trigger misfire codes.
Repair Cost Estimate
| Option | Est. Cost | Notes |
|---|---|---|
| Do It Yourself | $20-80 (OBD-II scanner to read code) | If you have basic tools and mechanical knowledge |
| Mechanic / Dealer | $150-400 (diagnostic + common fix); $1,500-3,500 (if catalytic converter replacement needed) | Includes diagnostic labor + parts |
About This Data
Dashboard warning light information compiled from Audi owner's manuals, OEM service documentation, SAE J2402 standards, and NHTSA guidance. This is an independent reference — not affiliated with or endorsed by Audi. All brand names, model names, and dashboard symbols are trademarks of their respective vehicle manufacturers.
Published: 2026-08-22 · Repair costs are national averages and vary by location. Always get multiple quotes before authorizing repairs.
⚠️ Red dashboard lights demand immediate action — continued driving may cause engine damage or brake failure. When in doubt, pull over and consult a certified mechanic.
By Patricia N. Simmons — Automotive Electronics Specialist
Patricia has spent 12 years researching instrument cluster diagnostics and dashboard warning light systems across 20+ automotive brands. She has analyzed over 500 OEM owner's manuals and SAE standards to compile this reference. Her experience includes field diagnostics with certified technicians, cross-referencing NHTSA technical service bulletins, and building practical decision guides that help drivers understand exactly what each warning light means — and whether they should keep driving or pull over immediately.
About Patricia · Published: 2026-08-22 · Updated: August 22, 2026
Related Warning Lights
Similar warning lights from the same make or related systems:
Frequently Asked Questions
Can I drive my Audi A4 with the Check Engine Light on?
If the light is solid, you can drive to a shop for diagnosis. If the light is flashing, pull over immediately — continuing to drive may cause severe engine damage or brake failure.
How much does it cost to fix the Check Engine Light on an Audi A4?
DIY cost estimate: $20-80 (OBD-II scanner to read code). Mechanic/dealer estimate: $150-400 (diagnostic + common fix); $1,500-3,500 (if catalytic converter replacement needed). Costs vary by location, shop rate, and whether additional components are found to be damaged during diagnosis. Always get 2-3 quotes before authorizing repairs.
What causes the Check Engine Light to come on in an Audi A4?
The most common causes include secondary air injection system failure, oxygen sensor malfunction, turbocharger boost pressure issues, EVAP system leaks, and ignition coil failure. The most common causes vary by model year and driving conditions. See the troubleshooting section above for model-specific diagnostic guidance.