'24 H.D. Duramax-Allison Cold Start Motion Surge in Park

Kerry Pulaski · December 17, 2023

This is a shocker. At 2500 miles new, around 20 to 25 degree ambient, cold start-up, Duramax goes into high idle right away. Still in Park, after a minute or so, I heard a Bang, looked over and saw the truck rock slightly. On level driveway, electric park brake was not set. Hearing that Bang and seeing any motion, scared the xxxx out of me.

So far this happened three times, when it sat cold below freezing for a day or two. I added the ScanGauge III, after the first "In Park Lurch", and found no Error codes to document.

Now at 4,500mi. on O.D., back to 3,500mi., it's been above freezing, and has not happened again.

I did not check yet, but does anyone know, if the H.D. column shift is a mechanical link to the Allison, or "By Wire" controlled ? Using the park brake ever since, even on the level just in case.

Next very cold start, will have cell video going to try & document.

ArrowsmithPML · December 17, 2023

2 hours ago, Kerry Pulaski said:

This is a shocker. At 2500 miles new, around 20 to 25 degree ambient, cold start-up, Duramax goes into high idle right away. Still in Park, after a minute or so, I heard a Bang, looked over and saw the truck rock slightly. On level driveway, electric park brake was not set. Hearing that Bang and seeing any motion, scared the xxxx out of me.

So far this happened three times, when it sat cold below freezing for a day or two. I added the ScanGauge III, after the first "In Park Lurch", and found no Error codes to document.

Now at 4,500mi. on O.D., back to 3,500mi., it's been above freezing, and has not happened again.

I did not check yet, but does anyone know, if the H.D. column shift is a mechanical link to the Allison, or "By Wire" controlled ? Using the park brake ever since, even on the level just in case.

Next very cold start, will have cell video going to try & document.

So at about -10 C and especially if I left I left the truck for a bit parked I would plug it in. Although not certain, my guess is that the transmission fluid and or oil sump and the associated circulation is cold and or not working.

Just my initial thoughts.

gemarsh · December 17, 2023

Yeah, it will do it within the first 2 seconds after ignition. When it's cold, I will reach in, left hand on brake pedal, right hand reaching in and hit start button.

Truck surged forward, what seemed like a foot when you're on the outside! It probably was only a rocking back and forth motion.

Truck must load up the transmission, like a power stall, to heat up fluid.

Does it every cold start that it idles up when cold.

A few minutes later it will unload the tranny and idle down a couple of rpm's.

64BAwagon · December 17, 2023

Even my gasser seems to load the trans up when cold started (not really that cold since its in the barn and the barn never gets below 45 degrees)

Kerry Pulaski · December 17, 2023

(@gemarsh)(@64BAwagon)(@AerosmithPML), Thanks all for the replies.

Starting to piece these events together, sounds like the programming on cold start gas or diesel, loads up the trans., for a friction and fluid circulation warm up ?

And no darn trans dipstick to also look at.

Will look tomorrow if the ScanGauge III, X-Gauge list has any readings for Trans Fluid Pressure, as it does for temp. That would be great to monitor cold and warm situations, and warm up events.

Ksilva211 · December 20, 2023

I’ve been questioning the startup on my 2024 as well. Definitely heats up fast and makes a lot of strange noises as well as a lot of condensation from the exhaust for the first three minutes when it’s cold. Not sure if anyone else’s is doing the same

Edited December 20, 2023 by Ksilva211

Kerry Pulaski · December 20, 2023

Reply from ScanGauge on the SC-III, X-Gauge Trans. Line Pressure Calculated PSI, Available Display........

See attached PDF. Has the X-Gauge Code to type in, to display the Trans. line Pressure......

I will give it a try today.

Replied to ScanGauge, if also a "MAX" Trans. Line Pressure Value Could Be Captured as well. This may help compare to the Normal Warm Line Pressure , when at Idle or in gear.

This am. at 30 degrees overnight. See if I get another cold start lurch during warmup.

Re 2024 GMC 2500HD SCANGAUGE III_TRANS FLUID PSI DISPLAY.pdf

Kerry Pulaski · December 20, 2023

Forgot to add @gemarsh and @64BAwagon, to their contributions on this subject. Thanks.

64BAwagon · December 20, 2023

I just added it to my SG3. I named it "TLINEPSI"

The truck was started and pulled out of the barn which was 46 degrees (29 outside ambient). By the time I entered the data and got the display up it was showing a value of "88" after the truck got to 175 deg and the trans to 90 deg it showed 84 at idle. I only pulled it to the end of the driveway, didnt drive it any distance.

Edited December 20, 2023 by 64BAwagon

Kerry Pulaski · December 21, 2023

Got this put in the SG-III this am. Call it "Trans PSI". Reads 80 PSI in Park at 650 RPM. Got up to 218 PSI at 1500 RPM in Park. This at 158/160 Deg. on Eng. Coolant, and 118 deg., Trans Temp.

Highway_80-85 PSI at 1500 RPM in 10th, gear at 70 MPH. Eng. Temp 180 Deg., Trans 120 Deg.

When warming up this am., at 30 Deg. Air, and Eng. Temp, went to 1000 RPM high Idle (Duramax 5LP).

After 1 min. Trans did a Lurch, for 1/2 Sec., then did another, about 30 sec. latter, tho not as harsh.

Then 2 min. latter High Idle off, to 650 RPM.

These Trans Lurch / Jerks happen so abrupt and short duration, for the sensor to catch it in real time.