wanted to ask if anyone has had this issue? Have a 04 PT Cruiser (turbo) I bought not running that had a ton of parts replaced, sensors, cat converter, turbo. reflashed PCM, timing belt. ect. Spent a lot of time going thru the engine, pulled the head, reseated the valves, new lifters and OEM O2 sensors, ended up replacing the PCM and injectors to finally getting it running great. over the last couple months I have been getting the PO420 code but when I check it the sensor checks good so I just reset it. 3 or 4 weeks later it will happen again. I run regular gas and don't drive a lot anymore and wondering if I should go mid-grade on the gas or start being picky about the brand? I use BP or speedway since they are the closest to me. Any suggestions form anyone. Thanks, Rich

 

YouTube search P0420 fix.
Spark plug extensions work well, never failed me and virtually undetectable at inspection.

 

Not a spark plug extension but extender for downstream O2 sensor. The O2 extender pulls the sensor out of the exhaust stream to slow down its reaction. A p0420 is set when there is not enough difference between the upstream O2 readings and the downstream O2 sensor reading. The upstream sensor will fluctuate a lot adjusting the air/fuel mix. After the cat has cleaned up the exhaust the downstream sensor will be relatively steady.

 

thanks for your response, I thought of that but just changing the sensor is difficult because there is no clearance between the cat and shielding its real tight so the extender wont fit. this year cruiser uses the same sensor in both positions as per Chrysler. because we are using what they term "summer blend" now I am thinking its the gas. never had this until then.
thanks again
Rich

 

summer winter blend is just the addition of more oxygen into the fuel mixture that's all .