2019 Silverado LD 5.3 throttle hangs open at cruise

[Pete D]

My 3 month old 2019 Silverado 5.3  6sp auto throttle does funny stuff on the freeway and descending hills. 

 

When I lift off the gas pedal in traffic at speed, the RPMs don't drop for at least an eighth mile. Cruise control on or off, makes no difference.  When descending hills, the truck picks up speed rapidly when you lift off the gas due to the "open" throttle.. Even downshifting descending a hill the truck picks up speed rapidly.  I find myself on the brakes constantly and unexpectedly to avoid slowing traffic ahead.

 

To confirm I wasn't losing my mind, I data logged the throttle position sensor while driving extensively.  It normally reads 14% absolute at idle and cruise with no pedal pressure.  Lifting off the gas on the freeway in high gear the TPS drops down to  21% for  about 10 seconds then goes down slowly to 14%.  The 14% feels fine, don't notice additional throttle.   Each time you touch and release the throttle it does the slow  return to idle thing. 

 

It's that 10 seconds or so of 21% unintended part throttle that's  driving me crazy.

 

Any ideas?

 

Thanks,        Pete 

 

[lucas287]

Definitely not normal. I'd be going to the dealer promptly as that sounds like a safety hazard. 

[M1ck3y]

Well, it doesn't sound mechanical because it function's fine otherwise? very weird

 

Maybe your pedal is sticking?

Edited October 15, 2020 by M1ck3y

[lucas287]

Just a quick note : There is a distinction between Accelerator Pedal Position and Throttle Position (your actual blade on the throttle body). Your pedal position influences throttle position (pressing the gas pedal to accelerate) and while they're mostly linear, the ECM can override the desired pedal position and tell the throttle to do whatever it wants, usually reducing throttle position as a function of torque management. 

 

But that's not your problem specifically. I just wanted to illustrate the difference. 

 

The dealer should be able to diagnose it pretty quickly. 

[Pete D]

Thanks Lucas287.  I've been thinking it's a programmed emissions reduction strategy.  I just noticed the scanner does have gas pedal position also  (ACC POS D+E).  Interesting.

 

Thanks for the feedback. It will go to the dealer.

 

Pete

 

 

[M1ck3y]

Lol, in other words and far less words; drive by wire. I have 20 bucks on a sticky pedal/sensor assembly.

[Pete D]

2 hours ago, M1ck3y said:

Lol, in other words and far less words; drive by wire. I have 20 bucks on a sticky pedal/sensor assembly.

You may be a winner. Note scanner read out above while idling at 625 rpm. The two accelerator position  sensors don't match.   ACC POS #D is 18.8 %.  ACC POS #E is 9.4 %.  GM TSB 07-06-04-019F  calls them APP sensors. This TSB  addresses accel pedal position sensors (1 and 2) being out of synch.  The TSB doesn't apply to 2019  (yet).

https://static.nhtsa.gov/odi/tsbs/2017/MC-10139090-9999.pdf

 

And to think I bought a new truck so I wouldn't have to work on it.. dream on.

[lucas287]

12 hours ago, Pete D said:

You may be a winner. Note scanner read out above while idling at 625 rpm. The two accelerator position  sensors don't match.   ACC POS #D is 18.8 %.  ACC POS #E is 9.4 %.  GM TSB 07-06-04-019F  calls them APP sensors. This TSB  addresses accel pedal position sensors (1 and 2) being out of synch.  The TSB doesn't apply to 2019  (yet).

https://static.nhtsa.gov/odi/tsbs/2017/MC-10139090-9999.pdf

 

And to think I bought a new truck so I wouldn't have to work on it.. dream on.

I wouldn't fret too much. An anomaly for sure! 

[Pete D]

Dealer reports " no codes, no problem. "   I don't want to tow anything with this throttle hanging open.  A few seconds of  rev hang I get it. 10 seconds or so is too long.

Edited November 27, 2020 by Pete D

[M1ck3y]

Did they test drive it?

[Pete D]

Customer states RPM stays higher than normal during shifting. Scan for codes.

 ROAD TESTED DURING/COLD OPERATING TEMPS & COULD NOT DUPLICATE CONCERN. SCANNED VEHICLE & NO DTC SET CURRENT/ HISTORY.

 

To the SA's credit he suggested bringing truck back if issue persists.  Not sure why they didn't use the word "Throttle" in the  service request but I can guess. 

[M1ck3y]

I've found emailing the lead service advisor or even the service manager is the best way to have a problem addressed. I've had service advisors completely distort what the actual problem is so that when the tech looks at it he's basically just wasting his time. It'd better if we could just skip the advisor all together. 

 

One time an  advisor tried and tell me my warranty was expired. She wouldn't stop talking about how GM Warranty works, so I just nodded my head. The whole time thinking, just get my truck in there and fixed. There's gotta be someone else down the line that will recognize my truck IS under warranty.