Top 5 Reasons Trucks Fail Clean Truck Check (And How to Avoid Them)
Blog Post 2: Top 5 Reasons Trucks Fail Clean Truck Check (And How to Avoid Them)
Prevent Costly Failures with These Pro Tips Call 916-890-4427
After conducting hundreds of Clean Truck Check inspections across Northern California, we've identified the most common failure points. Here's what causes trucks to fail and how you can avoid these expensive problems.
1. Ignored Check Engine Lights (40% of failures)
That amber warning light isn't just a suggestion. Any active emission-related fault codes will cause an automatic failure. Many operators ignore intermittent lights, hoping they'll go away.
Prevention: Address check engine lights immediately. Even if the truck seems to run fine, emission faults can worsen quickly. A simple sensor replacement today could save you from a major SCR system repair tomorrow.
2. Deferred DEF System Maintenance (25% of failures)
Diesel Exhaust Fluid (DEF) systems are notorious for problems when neglected. Crystallized DEF, faulty sensors, and clogged injectors are common issues we see.
Prevention:
Use only high-quality DEF from sealed containers
Replace DEF filters per manufacturer specifications
Don't let DEF tanks run empty
Address DEF warning messages immediately
3. Modified or Tampered Emission Equipment (20% of failures)
Any modifications to emission control systems result in automatic failure. This includes:
Deleted or bypassed DPF systems
EGR deletes or blocks
Modified ECU programming
Aftermarket exhaust modifications
Prevention: Keep all emission equipment stock and properly maintained. The short-term performance gains aren't worth the legal liability and compliance issues.
4. DPF Regeneration Issues (10% of failures)
Diesel Particulate Filters need regular regeneration cycles to function properly. Short trips and idle time prevent proper regeneration, leading to clogged filters.
Prevention:
Allow trucks to complete regeneration cycles
Schedule periodic forced regenerations
Consider manual cleaning every 100,000-150,000 miles
Monitor backpressure readings
5. Outdated or Incompatible Software (5% of failures)
Manufacturer software updates often address emission control issues. Running outdated ECU software can trigger fault codes that cause test failures.
Prevention: Stay current with manufacturer service bulletins and software updates. Many emission-related updates are covered under warranty.
Pro Tips for Test Day Success:
Pre-test your truck: We offer preliminary scans that identify issues before official testing
Clear historical codes: After repairs, ensure codes are properly cleared
Warm up the engine: Cold engines may not test properly
Check your paperwork: Ensure registration and insurance are current
The Mobile Advantage
When you schedule with NorCal CARB Mobile, we can perform a preliminary scan before the official test. If we identify issues, you'll know exactly what needs fixing—no surprises, no failed test on your record.
Remember: A failed Clean Truck Check doesn't just mean inconvenience; it means lost revenue, potential citations, and rushed repairs. Preventive maintenance is always cheaper than emergency fixes.
