Infinite Crank when Accelerator Pressed

[WalleyeMikeIII]

Had a scary experience at the car wash today. My Denali just cranked and cranked, no start; I let it crank for like 10s, no start. Tried about 5 times.

Hit OnStar, they ran remote diagnostic, no codes.

Disconnected negative battery terminal, let it off for 3 min. Reconnected…same symptom, crank, no start.

Looked down, the car wash tech installed the floor mat over the accelerator pedal. It was partially depressed. I fixed the floor mat; hit the start button…fired right up.

Net: don’t apply accelerator while starting!

Be nice if GM posted a message in the info cluster after this saying “Do not Apply Accelerator While Cranking”

 

[tom3]

Used to be the "clear flood" mode. Maybe it still is?

 

[WalleyeMikeIII]

Used to be the "clear flood" mode. Maybe it still is?

Probably, haven’t checked the owners manual yet. Throttle was not to the floor, just depressed slightly…

 

[Stbentoak]

Reason #32 why not to take your vehicle to an auto car wash…

 

[Joseph Garcia]

Be nice if the wash tech did his/her job correctly in the first place.

 

[Fless]

It wouldn't hurt to have a chat with the car wash manager to make him/her/it/they (don't want to assume anything related to preferred pronouns) aware of the safety issue that is caused by having the mat improperly reinstalled. The wash might have some liability, disclaimers or not.

 

[iamdub]

Had a scary experience at the car wash today. My Denali just cranked and cranked, no start; I let it crank for like 10s, no start. Tried about 5 times.

Hit OnStar, they ran remote diagnostic, no codes.

Disconnected negative battery terminal, let it off for 3 min. Reconnected…same symptom, crank, no start.

Looked down, the car wash tech installed the floor mat over the accelerator pedal. It was partially depressed. I fixed the floor mat; hit the start button…fired right up.

Net: don’t apply accelerator while starting!

As @tom3 said, it's the "Clear Flood" mode. With the older generations, the pedal needed to be pressed at least 80%. Maybe they reduced it for the newer generation.

Be nice if GM posted a message in the info cluster after this saying “Do not Apply Accelerator While Cranking”

It's an intended factory function, so they can't discourage it with such a message. Maybe a simple "ACCELERATOR APPLIED" or "CLEAR FLOOD MODE ACTIVE" message would do. It's such a rarely used function that there's no point. I've used it on mine plenty of times- not for clearing a flood, but to prime the oil system.

 

[WalleyeMikeIII]

As @tom3 said, it's the "Clear Flood" mode. With the older generations, the pedal needed to be pressed at least 80%. Maybe they reduced it for the newer generation.




It's an intended factory function, so they can't discourage it with such a message. Maybe a simple "ACCELERATOR APPLIED" or "CLEAR FLOOD MODE ACTIVE" message would do. It's such a rarely used function that there's no point. I've used it on mine plenty of times- not for clearing a flood, but to prime the oil system.

I actually don't think it was in "Clear Flood Mode" as it was not pressed all the way to the floor, but only partially. The infinite crank did not require me to continue to hold the start/stop button down, as referenced in the owners manual on pg 207, just a press and release, and cranking ensued until I hit the button again to stop the cranking.

This is a Throttle By Wire system, meaning that the accelerator pedal is simply a position sensor, which is read by the ECU, which then feeds electronic throttle inputs to the electronic throttle control.

I realize this ECU may be programmed differently, but I know first hand the implementation of Mercury Marine's ECU for their fly by wire outboards have issues if you start them and the throttle is not in the zero position, it throws off the calibration while driving.

I wonder if the GM design prevents actual engine start in this scenario of partially applied throttle input, to eliminate a mis-calibrated throttle...who knows, all I know is I hit the button and it cranked away w/ a no start, until I hit the button to stop it.

 

[iamdub]

I actually don't think it was in "Clear Flood Mode" as it was not pressed all the way to the floor, but only partially. The infinite crank did not require me to continue to hold the start/stop button down, as referenced in the owners manual on pg 207, just a press and release, and cranking ensued until I hit the button again to stop the cranking.
View attachment 370438

This is a Throttle By Wire system, meaning that the accelerator pedal is simply a position sensor, which is read by the ECU, which then feeds electronic throttle inputs to the electronic throttle control.

I realize this ECU may be programmed differently, but I know first hand the implementation of Mercury Marine's ECU for their fly by wire outboards have issues if you start them and the throttle is not in the zero position, it throws off the calibration while driving.

I wonder if the GM design prevents actual engine start in this scenario of partially applied throttle input, to eliminate a mis-calibrated throttle...who knows, all I know is I hit the button and it cranked away w/ a no start, until I hit the button to stop it.

Interesting. After reading that, I agree that it might not have been the Clear Flood Mode. That requires 80% or more throttle, but the book tells you to floor it since that's easier than trying to say "press to at least 80% throttle..." My old '08 is Throttle By Wire. It also starts by bumping the key rather than having to hold it, just like you pressing your button versus holding it. I can't say for sure if I've ever bumped the key with the pedal floored. I know it'll only allow a 10-second cranking interval before stopping even if the key is continuously held.

I'm thinking yours was more of a protection thing than a calibration thing. There's no reason to be on the throttle when starting. Imagine if someone were to immediately rev a really cold engine.

Now I'm prompted to go play with mine to see what happens at various pedal and key inputs...

 

[89Suburban]

Interesting. After reading that, I agree that it might not have been the Clear Flood Mode. That requires 80% or more throttle, but the book tells you to floor it since that's easier than trying to say "press to at least 80% throttle..." My old '08 is Throttle By Wire. It also starts by bumping the key rather than having to hold it, just like you pressing your button versus holding it. I can't say for sure if I've ever bumped the key with the pedal floored. I know it'll only allow a 10-second cranking interval before stopping even if the key is continuously held.

I'm thinking yours was more of a protection thing than a calibration thing. There's no reason to be on the throttle when starting. Imagine if someone were to immediately rev a really cold engine.

Now I'm prompted to go play with mine to see what happens at various pedal and key inputs...

Don't go tinkering leave it alone LOL!!!!