Chronic error code, P0335 + others

baskervi · May 17, 2018

Last spring the Yukon was throwing the P0420 error code for poor catalyst efficiency, so we replaced the catalytic converter last summer. I'll note that the plugs on the driver's side were light grey and looked good, but all plugs on the passenger side were very dark and sooty. I don't believe they were oily, but I did replace the plugs.

- A couple months later, we started experiencing chronic error codes on our 2007 Yukon XL 1500 5.3L. Initially, we were getting (among other codes) P0335 for the crankshaft position sensor and P0340 for the camshaft position sensor - these were always showing up, but there were usually one or two other codes that were with these. I replaced these sensors August of last year with genuine O'Reilly sensors and quickly replace them with genuine GM sensors from the dealer, but both error codes continued to come up frequently, and of course the Stabilitrak lamp would occasionally (sometimes frequently) come on and the truck would go into reduced power mode. We'd have to pull the battery terminal off just to get home. After repeatedly checking continuity of the wires, plus wiggling the wires while checking continuity, I couldn't find any problems in the connections. I rotated the crankshaft and made sure the proper signals were being generated at the sensors. Out of frustration, we ended up taking the truck to the dealership, and they said it was a bad motor mount and claimed they fixed a break in the wiring harness. I looked for a repair job to the wiring but couldn't find anything. I know those wires inside and out by now. The truck's been working fine until April.

Beginning last month, we started getting the P0335 error code regularly again, but we've also had a couple other ones pop up: P0420 for the reduced catalyst efficiency and P2119 for the throttle body.Yesterday, the stabilitrak came on 3x with the reduced power mode. Battery terminal came off each time, because my wife was across town, and fortunately she can use a wrench. I decided to take it right into the shop, because we're leaving town shortly and I don't have time to spend on this. The dealership wants to 1) replace the catalytic convert, 2) replace the CKP sensor, and of course 3) replace the throttle body.The dealership was not aware that the catalytic converter was replaced a year ago (with one that has a life time warranty, minus labor), but I know there is deeper problem that is being missed. We'd like to keep the truck, but I'm running out of ideas as to how what I can even try, and obviously the dealership isn't sure.

Does anyone have an idea of what might be going on? I presume there is a serious problem with the engine with the catalytic converter being fouled in a year, so is this correct? Besides the typical button logos coming off, the cracked dash, and super cheap plastic throughout, it's still in pretty good shape. And it's paid off. Thanks

txab · May 17, 2018

Did you think to check the downstream O2 sensor? Was a crank relearn ever performed?

baskervi · May 17, 2018

Thanks for the quick response. I forgot to mention we replaced front and rear O2 sensors on the passenger side only just before the catalytic converter was replaced.

txab · May 17, 2018

Mileage on vehicle? Mileage between cat change and now? Just curious. What were these "other" codes?

baskervi · May 17, 2018

218,000 miles on the truck currently. Sorry, but I don't recall the other codes - I just saw the CMP and CKP so often. Since you asked the question, I do believe the error code for the throttle body occasionally popped up. Mileage between cat change in now would be around 16-18,000 miles.

baskervi · May 19, 2018

Maybe some more information that may be useful. I've noticed on occasion that the battery charging meter will show the system is discharging. We got the P0335 CKP sensor message with Stabilitrak (borrowed a reader for a couple days to keep a log), but I happened to notice the battery gauge was reading about 15-20 degrees on the discharging side. I reconnected the negative terminal and made sure we had a good connection, and for 5 minutes everything read OK, and then the needle started dropping. I can't do anything to bring it back up. It's not throwing an error at the moment, though.