P0420 on Your 2024 Acura MDX: What to Know
A P0420 trouble code on your 2024 Acura MDX means the ECM has detected reduced catalytic converter efficiency on Bank 1. The 2024 MDX continues with the 3.5L V6 engine producing 290 horsepower in standard trims and the 3.0L turbocharged V6 producing 355 horsepower in the Type S. Getting this code on a nearly new luxury SUV is unexpected, but the good news is comprehensive warranty coverage.
Let's look at what's likely causing the code and what your next steps should be.
Symptoms
- Check engine light on — The main indicator
- Normal driving feel — The MDX should perform as expected
- Slight MPG change — Barely noticeable
- Possible exhaust odor — Faint sulfur smell
- Emissions failure — In testing states
Likely Causes
1. ECM Software Issue
Honda and Acura regularly release software updates for their emissions monitoring systems. The 2024 MDX may have catalyst monitoring thresholds that need refinement. A software reflash is often the quickest and simplest fix for a new vehicle P0420.
2. Faulty O2 Sensor
A factory-defective downstream oxygen sensor on Bank 1 can cause false P0420 readings. The sensor may have a manufacturing defect or could have been contaminated during production. This is a straightforward warranty replacement.
3. Catalytic Converter Manufacturing Issue
Although Acura's quality control is excellent, the occasional converter with insufficient catalyst coating or internal defects can make it through. On a 2024 model, this is clearly a warranty repair.
4. Exhaust Connection Issue
A gasket or connection that wasn't properly sealed during assembly — whether at the exhaust manifold, converter inlet, or any other junction — can create a small leak affecting sensor readings.
What to Do
- Visit your Acura dealer — This is a warranty repair. No out-of-pocket cost expected.
- Request a TSB check — Ask about any Technical Service Bulletins for the 2024 MDX.
- Keep service records — Document all visits and repairs.
- Continue driving normally — No changes needed to your routine.
Cost Estimates (If Out of Warranty)
- ECM software update: $0 under warranty ($100 – $150 otherwise)
- O2 sensor: $0 under warranty ($140 – $340 otherwise)
- Catalytic converter: $0 under warranty ($1,400 – $2,700 otherwise)
- Exhaust leak fix: $0 under warranty ($100 – $400 otherwise)
Safe to Drive?
Completely safe. Your 2024 MDX's safety systems, SH-AWD system, and driving dynamics are unaffected by a P0420 code. Schedule a convenient dealer appointment and continue enjoying your SUV.
Prevention
- Use Top Tier fuel — Quality gasoline keeps the engine running clean
- Follow the maintenance minder system — Acura's maintenance alerts guide proper service timing
- Address all warning lights — Prompt attention prevents secondary damage
- Use the recommended engine oil — Proper oil viscosity and quality matters