Intermittent P0121

elite0259 · October 16, 2014

Hey guys I have been having a problem where every couple of weeks my CEL will come on and spit out P0121 (07 NNBS CC 1500 5.3L). It has been happening for a few months where it'll pop on, I'll clear it, it'll go away for a few weeks and come back. Over the weekend it came on a few times, each time I cleared it and it stayed off but came back after a little while (timing and on/off cycles were inconsistent). Now I cleared it again sunday and it's stayed off for the week but does anybody know why it'd be intermittent? I'd hate to blow a lot of money to replace the TB assembly if I don't have to...

XYZ · October 17, 2014

Read this recent thread...http://www.gm-trucks.com/forums/topic/165385-2003-hd1500-reduced-power-mode-back-to-the-drawing-board/

Try probing /wiggling the wires going to the throttle body, if your problem is inconsistent, this is a good place to start, and it is a known issue.

elite0259 · October 20, 2014

I didn't get reduced power though, just the CEL... it's now been over a week since I've seen it, I'm just waiting for the day that reduced power pops up :/

cs300823 · October 22, 2014

I had the same problem happen to me on my 07 NBS VMax...I had the check engine light come on & off for several months before I even had it checked. I finally a few weeks ago took it to the dealer and they serviced the throttle body and with no avail the light has not come on since...from what the dealer told me it was common problem and supposedly it was to be serviced every 50k so I guess I got my money worth out of that issue lol !!!

elite0259 · October 23, 2014

do you know what they did to service it? came back on tonight... but went away when I reset the light... Might have something to do with the rain since it was wet out the weekend before I posted this too

GMCustomerService · October 23, 2014

Hey elite0259,

Sorry to hear you're having issues with your CEL. I see you're considering going to the dealer to get this checked out, and I'm glad to assist in that process if interested. Just send a private message with your full contact information, VIN, mileage, and preferred dealer to discuss things further. Looking forward to hearing from you.

Sincerely,

Eddie A.

GM Customer Care

cs300823 · October 23, 2014

do you know what they did to service it? came back on tonight... but went away when I reset the light... Might have something to do with the rain since it was wet out the weekend before I posted this too

All they do is remove the throttle body clean it and reprogram.... The thing has run great every since ;-)