P0420 on a Chevy Malibu or Equinox: What the Code Means and What to Check First
What the Code Means
P0420 is the catalyst system efficiency code for bank 1. On the 3.6L V6, P0430 covers bank 2. The ECU compares the sensor before the converter with the one after it. A code means the converter is not behaving like a healthy one. It does not tell you why.
Common Causes to Check First
- Oil consumption. Check the oil level between changes. On the 2.4L, oil reaching the exhaust can contaminate the converter, and repairing the engine comes before replacing parts.
- Exhaust leaks. A leak ahead of the rear sensor skews the readings. Check the manifold and flange joints.
- PCV and fuel trim. Look at fuel trims on a scan tool for signs of vacuum leaks.
- Misfires. Check plugs and coils, and look for stored misfire codes.
- Sensor age. Compare front and rear sensor live data.
Sensor Location and Thread
The 2.4L has one rear sensor, called sensor 2 on a scan tool. The 3.6L has one per bank. We have not confirmed the sensor thread across all Malibu and Equinox years, so check that your sensor is M18x1.5 before ordering anything that threads into the bung.
If the Catalyst Has Failed
If testing shows the converter has failed, the repair is a compliant replacement converter. Look up any extended coverage on your engine with a dealer first, then recheck the monitors after a full drive cycle.
The Part We Make
Our 90 degree O2 sensor spacer, M18x1.5, is made for the downstream sensor bung. Check your own sensor thread before you buy anything for it.
Two downstream sensors (V6 or V8): get the two pack
FAQ
Should I deal with oil use first?
Yes. If the engine is burning oil, a new converter can be damaged by the same cause.
Is the rear sensor the same on every year?
Not necessarily. Verify the thread and connector on your year.
Legal note: designed for modified/off-road use. Check local emissions laws.
Written by Brockett Built in central Illinois.