Failing Utah's emissions test means your vehicle's exhaust exceeds the state's pollutant thresholds—and your registration can't be renewed until it passes. The most common causes are a worn catalytic converter (especially on vehicles over 100,000 miles), a failing oxygen sensor skewing the fuel mixture, or an engine misfire sending unburned fuel into the exhaust. The key to a successful repair is accurate root-cause diagnosis: replacing the catalytic converter on an engine that's running too rich or misfiring will result in the new converter failing prematurely. We find the underlying cause first, so the repair sticks and your vehicle passes on the retest.
Emissions failures require finding the root cause, not just replacing the component that's over the threshold. We scan for fault codes, evaluate oxygen sensor response times and signal quality, check catalytic converter efficiency codes in detail, and look for any underlying engine conditions—misfires, rich fuel trims—that would damage a new converter. Our goal is for your vehicle to pass the retest on the first attempt, not just get it close. Learn more about our Catalytic Converter Service service.
From diagnosis to repair, we keep you informed every step of the way.
Call or text us to describe what you're experiencing.
Bring your vehicle in for a thorough inspection.
We explain what we found and quote before any work begins.
Experienced technicians complete the repair with quality parts.
We test drive and verify the repair before returning your car.
The most common causes are a worn catalytic converter that can't reduce pollutants below Utah's threshold, a failing oxygen sensor skewing the fuel mixture, engine misfires sending raw fuel through the exhaust, or EVAP system leaks. Each has a specific diagnostic code that tells us what system is involved—but the code alone doesn't tell us why the component failed.
Costs vary widely depending on the actual cause. An oxygen sensor replacement runs $150–$300. An EVAP leak repair is $100–$400. A catalytic converter is $800–$2,500 depending on the vehicle. We diagnose the root cause first—replacing a converter on a misfiring engine will fail the new converter within months.
We diagnose the exact failure cause, make the repair, and verify readiness monitors are complete using our own testing equipment before returning the vehicle. Our goal is a first-attempt retest pass, not just getting close to the threshold.
These are the most common reasons drivers experience this symptom.
A converter past its service life can't reduce CO, HC, and NOx to Utah's passing thresholds.
A slow or dead O2 sensor causes incorrect fuel mixture, raising exhaust emission levels.
An upstream exhaust leak introduces outside air, causing false lean readings and incorrect fuel trim.
Misfires send raw unburned fuel into the exhaust, overwhelming the converter and failing the test.
Not sure if this is your issue? Browse other common problems we fix.
Contact Scott's Auto and Clutch today for honest service and expert repairs.
144 W Crystal Ave, South Salt Lake, UT 84115