Multi-code OBD2 diagnosis
Enter all the codes your scanner showed, not just the first one. We give you the overall severity, whether you can keep driving, the order in which to check them and how they relate to each other.
Summary
- Overall severity
- Medium
- Can I keep driving?
- Yes, but with caution
- Estimated cost
- $100 to $1,500
- Codes analyzed
- 1 of 1
The order below is the recommended one: first the codes that can cause the others. After each repair, clear the codes and check which ones come back.
Order of inspection
P0421 Warm Up Catalyst Efficiency Below Threshold (Bank 1) Medium
The P0421 code means the catalytic converter closest to the engine, the one that starts working first, is not converting exhaust gases the way it should. Before you replace it, rule out exhaust leaks, worn O2 sensors and whatever may have damaged it, because the replacement is one of the most expensive parts on the vehicle.