2012 Colorado with Factory 5.3 LH9. Truck running absolutely fine prior to below.

Took off part of exhaust and cat and disconnected downstream and upstream o2 sensors to weld a bung in for a wideband.

Bolted back up and screwed the two o2 sensors back in with the new bung capped off.

Truck immediately ran very rough and threw the p0300 code. Disconnected the battery for 20 min. and started back up….same thing.

Replaced both sensors and truck still running rough and wants to quit after slight acceleration and giving me a flashing check engine light.

Any suggestions....I don't get it.

 

Broken O2 sensor wires? They get brittle after sixteen years. Look at the OBD2 data and my guess is that at least one sensor will show zero response. No kidding AC Delco O2 sensors as the replacements or some cheesy, offshore pretenders? Denso or Bosch would be the only others I would consider.

Rick

 

Thanks. I used Denso as I've never had an issue with them in the past.

I haven't traced the wires back to the harness, but they all look good from what I can tell.

My cheap scanner only shows that one code. Truck doesnt see snow so need to find a better scanner or wait until spring.

 

P0300 code is for misfires... rear o2's wouldn't cause that...

Check coils, spark plugs, plug wires...

Make sure plugs fully installed...

Make sure no cracked ceramics on any plugs...

Make sure plug wires are fully snapped on to plugs & coils (have seen people before find that plug wires have slipped off, or even plugs themselves have loosened up and come out)...

Also, get a can of CRC Mass Airflow Sensor Cleaner and clean the MAF sensor, and make sure it's re-installed facing the correct direction...