Firestorm500

2006 Grand Cherokee Laredo, 3.7 V6, 4 X 4 recently bought for my daughter.

Check engine light keeps coming on with several codes. I just had all 4 O2 sensors replaced last week. Light stayed off for a while, but when I moved her Jeep on Sunday I saw that it was back on again.

Took it back to the mechanic's shop. They scanned it and said that code P0420 is showing, which is catalytic converter efficiency below threshold.

I chase this code all of the time on my wife's Cadillac Northstar. I have replaced the converter twice on her car, but the code still comes back from time to time.

Has anyone replaced both cats on a 2005-2010 Grand, and did the computer no longer throw this code?

bones99xj

How many miles are on the GC. If it's with in 8 years 80k, federal emission warranty will replace.

Firestorm500

148,200.

My mechanic's opinion is that the failed O2 sensors, both on bank one, probably got the catalytic converter when the previous owner failed to correct the problem in a timely manner.

Firestorm500

OK here's an update.

Over a 4-week period, I ended up replacing all four O2 sensors and both catalytic converters with high-efficiency ones.

The front O2s were replaced twice because the first set was defective. They were NTKs, so that was surprising.

Took 4 trips to the exhaust shop, and at least 5 to the mechanic to reset the light.

After 700 miles since all this, the light is staying off. Finally.