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2012 LML high idle not working

14K views 16 replies 5 participants last post by  smokinu454 
#1 ·
Hey guys. Haven't posted here in a very long time. Sold my LLY for a 2012 LML Sierra SLT. My question is what am I doing wrong? E brake set, 0 MPH, truck is in park, cruise on, I press set and the DIC says fast idle on but it continues to sit at 650RPMs. Am I missing something or is it messed up. No tpms or service engine/service anything lights by the way.
 
#2 ·
Sounds like what you're doing is correct, as long as you're also not pushing brake and not pushing throttle?


(If you're wanting to use it to warm coolant and transmission up when it is below 32F, the 'elevated idle' is more effective, and will start on it's own after a remote start.)
 
#3 ·
High idle & Elevated idle are 2 different things.

High idle isnt a standard feature. If you have this option you turn it On/Off by pressing the cruise control set button with the parking brake set. (This feature isnt really for faster warm ups but it does work.)

Elevated idle is standard. On/Off with the DIC. When its turned on the outside temp has to be 32F or below & Coolant temp 150F or below. (This feature is what youd want to use for faster warm ups when the temps apply.)
 
#4 ·
When I try to activate the high idle feature I am not pressing the brake or the accelerator and I do have the factory option rpo code uh3 I believe. I am pretty sure that the elevated idle is working. I cannot select it through the DIC for some strange reason but using the accelerator and brake pedal trick I can get the DIC to read elevated idle on. When I cranked the truck this morning it was about 25° outside and the engine was cold the truck idled at 950 but the RPMs would not drop when I hit the brake. I went inside and came back out and the truck was at 104 degrees and it was idling at 650. Sound right? I honestly thought elevated idol for cold-weather was at 1050 rpms
 
#5 · (Edited)
Sounds like elevated idle is not working (or maybe not on).

Elevated idle sometimes waits a little (few minutes, depending on how cold it is) before increasing idle to 1050rpm, but it should then stay active until coolant reaches 150F or ambient reaches 32F or brake applied or throttle applied or speed detected or transmission moved from P or N.

If you have DIC buttons, you should be able to enable or disable it with them. I've never heard a good reason to ever disable it (but there might be one).
 
#7 ·
Brake lights don't stay on and cruise control works fine without kicking off.
 
#8 ·
The only other thing I could think of would be something tuning, but since you're all stock, I'm stumped. Other than making sure you have the right rpo code.
 
#9 ·
I do have a flashpaq but the problem stays the same after the truck is set to stock or tuned.
 
#10 ·
Are there any fuses or relays that's could be causing a problem? Would unhooking the batteries for an hour or so and hooking them back up help anything reset maybe?
 
#11 ·
Not sure on that. Someone else will have to chime in, but it wouldn't hurt to try unhooking the batteries, and letting it sit.
 
#12 ·
Unhooked both batteries and let it set for a while. Still no luck
 
#14 ·
I Googled it to be sure. Turns out it is uf3. But yes I do have that one for sure.
 
#15 ·
Also for the hell of it I disable elevated idle and the truck is still idling at 900 until near 100 degrees
 
#16 ·
I just had the dealer add this option to mine...I had to have Kory redo my tunes with the updated files, then it worked. but I see your stock.....I know sometimes I have to hit the set button twice, and sometimes I have to hit the cruise off then back on and it works....assuming our reading the codes from the glove box to know you have that option, it may be something the dealer needs to reflash the ECM/ BCM...when they did mine it would register on the dash telling me that the high idle was active but the dcm wouldn't respond. It was because the BCM had the updated calibration but the ECM had the "stock" calibration because I had flashed korys tune in from before the option was added.....
 
#17 ·
Sounds like exactly what mine is doing. Next time I get a chance I will have the dealer reflash the ecm. I am planning to have the tcm reflashed anyways due to a service bulletin that I found that explains my harsh 6-5 downshift when under load.
 
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