Intermittent P0300 Code
Thread Starter
Racer
Joined: Dec 2022
Posts: 273
Likes: 142
From: North Central Ohio
Intermittent P0300 Code
I am getting a very intermittent P0300 code and only when engine is idling. Engine will run fine for multiple days, no codes present, and then throw the code, especially after shutting down after a drive and the starting again several hours later. This has happened on 3 separate occasions, days apart. Plugs are brand new, wires are less than 2 years old and well seated on the plugs and coil packs. While observing live data on my scan tool, saw multiple misfires on the entire right bank at idle, but when running the RPM's up to about 1500, misfires quit. The short term fuel trim on the right bank runs slightly below the left bank consistently. Fuel injectors are all brand new, (ordered from Summit, not ebay or amazon). Curiously, while I was idling the engine, the DIC showed a P0300 code as current, but then cleared itself, showing no codes present in the PCM. Any suggestions as to where to start looking now?
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,430
Likes: 3,981
From: Cape Coral, Florida
If it’s a bank specific misfire look at your Bank 2 O2 sensor…is it’s oscillating between 200-800 mv’s that perfect or is it “stuck” lean like say 100mv’s ??…if you see that the PCM will “over fuel” and the car will run rich…if it is “stuck” rich the PCM will “take away” fuel and the car will run lean…either way the car will run poorly and likely misfire.
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,430
Likes: 3,981
From: Cape Coral, Florida
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,430
Likes: 3,981
From: Cape Coral, Florida
Ok, so it looks like it’s “stuck” rich…remove the O2 connector and then pull the O2 heater fuse…now turn the key on and with your scan tool see if that O2 sensor shows 450mv’s…it it does the O2 sensor is bad…I preferred Denso sensors on the C5’s…you can get one at Autozone.
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Thread Starter
Racer
Joined: Dec 2022
Posts: 273
Likes: 142
From: North Central Ohio
I don't buy parts from either of those! My nearest autozone does not have the Denso, The bad one looks to be an almost new Bosch. Off to Summit to order the Denso! Good thing about being here in Ohio, I get stuff from them usually next day!