What Does P0420 Mean on Your 2024 GMC Acadia?
A P0420 code on your 2024 GMC Acadia means the engine control module has detected that the Bank 1 catalytic converter isn't meeting efficiency requirements. The completely redesigned 2024 Acadia rides on the new GM C1 platform and is powered by the 2.5-liter turbocharged four-cylinder engine producing 328 horsepower and 326 lb-ft of torque, paired with an 8-speed automatic transmission. AWD is available on most trims.
The ECM evaluates converter health by comparing upstream and downstream oxygen sensor data. When the downstream sensor starts producing voltage patterns similar to the upstream sensor's rapid switching, the system determines the converter has degraded.
Symptoms to Watch For
- Check engine light illuminated
- Slight fuel economy decrease
- Sulfur smell from exhaust
- Emissions test failure
- Normal driving performance
Common Causes on the 2024 Acadia
1. Catalytic Converter Manufacturing Defect
The 2024 Acadia is a completely redesigned vehicle with a new platform and engine. First-year production can have quality variations in the converter or exhaust system. The new 2.5L turbo engine produces significant heat through the close-coupled converter.
2. O2 Sensor Defect
A factory-defective downstream sensor is a leading cause on new vehicles. The new platform's sensor calibration may have initial variations.
3. Exhaust System Assembly Issue
First-production vehicles occasionally have assembly-related exhaust leaks at gasket or connection points. The new platform's exhaust routing may have areas prone to minor leaks.
4. ECM Software Calibration
The completely new platform and engine will receive software updates as GM refines the calibration. Catalyst monitoring thresholds may need adjustment.
Diagnostic Steps
- Take it to your GMC dealer — fully under warranty.
- Check for software updates — critical on a first-year redesign.
- Scan for all codes.
- Monitor O2 sensor data.
- Inspect exhaust connections.
Repair Cost Estimates
Under warranty, free. Reference costs:
- Catalytic converter: $800 – $2,000.
- O2 sensor: $140 – $360.
- Exhaust leak repair: $100 – $350.
- Software update: $100 – $200.
Is It Safe to Drive?
Yes, P0420 is safe. The 2024 Acadia is under GMC's 3-year/36,000-mile bumper-to-bumper warranty, 5-year/60,000-mile powertrain warranty, and the 8-year/80,000-mile federal emissions warranty. Take it to your dealer.
Prevention Tips
- Use quality fuel
- Follow GMC's maintenance schedule
- Keep all software updates current
- Address any warning lights promptly
- Accept all recall and TSB repairs