What Does P0420 Mean on Your 2022 GMC Terrain?
A P0420 code on your 2022 GMC Terrain means the engine control module has detected that the catalytic converter isn't meeting efficiency standards. The 2022 Terrain (D2 platform) is powered exclusively by the 1.5-liter turbocharged four-cylinder engine (L3A/LFV) producing 170 horsepower and 203 lb-ft of torque, paired with a 9-speed automatic transmission. FWD is standard with AWD available.
Since the Terrain has a four-cylinder engine with a single bank, P0420 refers to the only catalytic converter in the system. The ECM compares upstream and downstream O2 sensor data to monitor converter health continuously.
Symptoms You'll Notice
- Check engine light on
- Slight fuel economy decrease
- Sulfur smell from exhaust
- Emissions test failure
- Normal driving behavior
Common Causes on the 2022 Terrain
1. Catalytic Converter Degradation
The 2022 Terrain has been in service for a few years, and the 1.5T engine's turbocharger produces hot exhaust that passes directly through the close-coupled catalytic converter. City driving with frequent short trips can accelerate converter wear as the converter doesn't always reach optimal operating temperature.
2. Downstream O2 Sensor Failure
The post-catalyst oxygen sensor on the 1.5T engine can degrade with heat and time. A sensor reading inaccurately will trigger P0420 even with a functional converter.
3. Exhaust Leak
The turbo-to-downpipe connection and converter gaskets can develop leaks from thermal cycling. The Terrain's compact engine bay means exhaust components are tightly packaged.
4. Oil Consumption Contaminating Converter
Some GM 1.5T engines have been reported to consume oil at higher-than-expected rates. Oil entering the exhaust contaminates and degrades the catalytic converter's precious metal coating.
Diagnostic Steps
- Scan all codes with a GM-compatible scanner.
- Monitor O2 sensor data to assess converter efficiency.
- Check oil consumption rate between changes.
- Inspect exhaust for leaks.
- Check for GM TSBs related to the Terrain.
Repair Cost Breakdown
- Catalytic converter replacement: $600 – $1,500 OEM; $350 – $900 aftermarket.
- O2 sensor: $120 – $300.
- Exhaust leak repair: $80 – $280.
- Oil consumption diagnosis: $100 – $300.
Is It Safe to Drive?
Yes, P0420 is safe. Check warranty status — GMC's 5-year/60,000-mile powertrain warranty may still apply, and the federal emissions warranty covers converters for 8 years/80,000 miles.
Prevention Tips
- Use quality fuel
- Monitor oil levels between changes
- Take highway drives regularly
- Follow GMC's maintenance schedule
- Address engine issues promptly