Auto start stop troubleshooting.

repairman54 · April 26, 2023

Auto stop may not work for a few cold startup cycles after opening the hood.

I found this out on my old '15 Malibu. I bought it used so I was opening the hood a lot checking things like oil and coolant and looking for potential issues.

redwngr · April 26, 2023

And there is also the reasons listed in the OM.

To maintain vehicle performance, other conditions may cause the engine to automatically restart before the brake pedal is released.

Auto Stops may not occur and/or Auto Starts may occur because:

. The climate control settings require the engine to be running to cool or heat the vehicle interior.
. The vehicle battery needs to charge.
. The vehicle battery has recently been disconnected.
. Minimum vehicle speed has not been reached since the last Auto Stop.
. The accelerator pedal is pressed.
. The engine or transmission is not at the required operating temperature.
. The outside temperature is not in the required operating range.
. The vehicle is shifted out of D (Drive) to any gear other than P (Park).
. Certain driver modes have been selected. -- See Driver Mode Control pg 242 and Four-Wheel Drive pg 233.
. The vehicle is on a steep hill or grade.
. The driver door has been opened or the driver seat belt has been unbuckled.
. The hood has been opened.
. The Auto Stop has reached the maximum allowed time.

AT4 owner · November 16, 2023

I have a 2019 GMC Sierra, original battery still (also in Southeast TX). Probably about time for me to change that. It's interesting you mentioned the trans fluid. I would have never guessed that, but recently with the cooler weather my auto stop/start stopped engaging.

MadMatt3883 · November 18, 2023

On 11/16/2023 at 11:55 AM, AT4 owner said:

I have a 2019 GMC Sierra, original battery still (also in Southeast TX). Probably about time for me to change that. It's interesting you mentioned the trans fluid. I would have never guessed that, but recently with the cooler weather my auto stop/start stopped engaging.

Well I’m going to have to correct myself on that now. I ended up replacing the trans cooler thermostat and installing a superior transmissions STL0101. The cooler flow is now always open and the transmission fluid usually doesn’t go above 120ish unless I’m in rush hour traffic. The start stop works all the time now, even when the truck isn’t at operating temperature. I’m not sure what the original issue was. The start stop got annoying real fast and I just disable it now.