P0300 o2 sensor? LH9
Thread Starter
Teching In
Joined: Jun 2025
Posts: 2
Likes: 1
P0300 o2 sensor? LH9 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.
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.
TECH Fanatic
Joined: Dec 2017
Posts: 1,467
Likes: 265
From: Bossier City, Louisiana
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
Rick
Thread Starter
Teching In
Joined: Jun 2025
Posts: 2
Likes: 1
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.
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.
LS1Tech Sponsor
Joined: Dec 2005
Posts: 2,932
Likes: 12
From: CT
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...
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...
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2014 Camaro 2SS/RS - LS3, 6-speed manual, short-throw performance shifter, NPP dual-mode performance exhaust, 1LE front splitter, ZL1 rockers, Z28 Rear Spoiler, all paint-matched Red Rock Metallic, BMR strut tower brace, Cold Air Inductions cold air intake, Apex Motorsports, Inc. catch-can, Custom DiabLew Tune
www.diablewtune.com -- www.diablocustomtune.com -- www.diablocustomtunegm.com
06MonteSS / DiabLew Tune
2014 Camaro 2SS/RS - LS3, 6-speed manual, short-throw performance shifter, NPP dual-mode performance exhaust, 1LE front splitter, ZL1 rockers, Z28 Rear Spoiler, all paint-matched Red Rock Metallic, BMR strut tower brace, Cold Air Inductions cold air intake, Apex Motorsports, Inc. catch-can, Custom DiabLew Tune
www.diablewtune.com -- www.diablocustomtune.com -- www.diablocustomtunegm.com
