Battery died and now my ASS is back

[airline tech]

Yeah, I don't see that this tech does a lot that's useful.



A wonderful step not mentioned in the manual. Thanks! I'll track down a what do.

It is in the manual

Connect the battery.
Refer to: Battery Disconnect and Connect (414-01 Battery, Mounting and Cables, General Procedures).

If installing a new battery, use the scan tool to carry out the Battery Monitoring System (BMS) reset after the battery is connected.
----------------------------------------------------------------------------------------
The easiest way is to do the reset via scan tool but there is an alternate method posted in various places on this forum - Brake Pedal (Method) this method is not in the service manual


I will try to clear up - what most likely happened as far as the ASS (Disabled and Enabled)
Yes - the Low Battery might have cleared the code for the BMS sensor reading (Unknown SOC) as it was most likely (Biased - Low) this alone would keep ASS disabled
When you charged the battery - How did you connect the (Negative) cable?
If you connected directly to the (Negative) Terminal, the BMS sensor would have never saw that you charged it - and the ASS would stay (Disabled)

If you (Charged) properly - Negative to Body Ground, then the BMS sensor saw the charge current being applied - however the sensor may have been biased so low that it did not register it as 100% even if the battery was at full charge

I think cycling the (Tow Haul Switch) triggered a Can Bus (Message) to disabled the ASS and when the (Tow-Haul) was deselected via the switch or next engine start and add in your recent battery charge - forced the BCM to (take another look at the current SOC) and it saw it was above the Threshold -and the ASS finally (Enabled)

The initial (Root) issue is the BMS Sensor (was biased Low) and out of range, which was enhanced by the (Short Trips + High IR in the Battery) and it appears you had some kind of (Can-Bus) message that was stuck in memory

You also mentioned - a possible tune, I do not know specifics about the Tunes, but I know there is a (Tow-Tune) - That may have something to do with it, and I am only using your experience as - It started working after you used (Tow Mode) via the Trucks Switch - Just a possible (Theory)

I think the whole issue is just a chain of events between the BMS System & Can Bus Communication & (Low Battery + High Battery IR)

Switch (Understanding) - The switches on the console are (Momentary Switches) they are not latched - when they are pressed, they send a (Pulsed) Can Bus Message

The switch is a 5-Volt Ref and every time you press the button - you send a pulse to grd
and when you do this - (Internal logic) of the modules see a Bit Logic Flip (0) to (1)
0= Normal Position - 1 = Non- Normal Position (Switch Deponent - Disable/Enable Feature)

Example - ASS Switch Press - Changes to (1) and ASS is disabled for the current key cycle
Example - Tow/Haul Press - Changes to (1) and the Tow Haul Mode is enabled for the current key cycle.
Press them again and they change to (0) - flipping the (Bit Logic)

The ASS Eliminator Modules - Installed in line with the switch, they remember the last switch position (when the truck was turned off) and when you start the truck, the aftermarket module pulses the switch to ground (if needed)

If you had the ASS (Disabled) Last drive - at next ignition cycle it pulses the switch to ground for you to satisfy the can bus logic.

If you had the ASS (Enabled) Last drive - then the module does not send a pulse to ground

Think of it as - The George Jetson - Button Presser

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[TruckBox]

I make a point to never leave the keys in the vehicle especially now that this one doesn't have they keypad... if the dumb thing will lock its doors when the battery dies.... no exceptions. lol

If the previous owner disconnected the BMS, you never would have had the ASS come on and it’s quite possible that no one would have noticed it was disconnected until your shop checked/charged your battery. The tech may have reconnected it and not noted it or said said anything to the service advisor.

Of course, it started working on its own, just as it should.

I did the charging and swap. Didn't reconnect any cables, but in swapping the new in did see what i'm pretty sure others have said to unplug to disable it. It is firmly seated.

It is in the manual

Connect the battery.
Refer to: Battery Disconnect and Connect (414-01 Battery, Mounting and Cables, General Procedures).

If installing a new battery, use the scan tool to carry out the Battery Monitoring System (BMS) reset after the battery is connected.
----------------------------------------------------------------------------------------
The easiest way is to do the reset via scan tool but there is an alternate method posted in various places on this forum - Brake Pedal (Method) this method is not in the service manual


I will try to clear up - what most likely happened as far as the ASS (Disabled and Enabled)
Yes - the Low Battery might have cleared the code for the BMS sensor reading (Unknown SOC) as it was most likely (Biased - Low) this alone would keep ASS disabled
When you charged the battery - How did you connect the (Negative) cable?
If you connected directly to the (Negative) Terminal, the BMS sensor would have never saw that you charged it - and the ASS would stay (Disabled)

If you (Charged) properly - Negative to Body Ground, then the BMS sensor saw the charge current being applied - however the sensor may have been biased so low that it did not register it as 100% even if the battery was at full charge

I think cycling the (Tow Haul Switch) triggered a Can Bus (Message) to disabled the ASS and when the (Tow-Haul) was deselected via the switch or next engine start and add in your recent battery charge - forced the BCM to (take another look at the current SOC) and it saw it was above the Threshold -and the ASS finally (Enabled)

The initial (Root) issue is the BMS Sensor (was biased Low) and out of range, which was enhanced by the (Short Trips + High IR in the Battery) and it appears you had some kind of (Can-Bus) message that was stuck in memory

You also mentioned - a possible tune, I do not know specifics about the Tunes, but I know there is a (Tow-Tune) - That may have something to do with it, and I am only using your experience as - It started working after you used (Tow Mode) via the Trucks Switch - Just a possible (Theory)

I think the whole issue is just a chain of events between the BMS System & Can Bus Communication & (Low Battery + High Battery IR)

Switch (Understanding) - The switches on the console are (Momentary Switches) they are not latched - when they are pressed, they send a (Pulsed) Can Bus Message

The switch is a 5-Volt Ref and every time you press the button - you send a pulse to grd
and when you do this - (Internal logic) of the modules see a Bit Logic Flip (0) to (1)
0= Normal Position - 1 = Non- Normal Position (Switch Deponent - Disable/Enable Feature)

Example - ASS Switch Press - Changes to (1) and ASS is disabled for the current key cycle
Example - Tow/Haul Press - Changes to (1) and the Tow Haul Mode is enabled for the current key cycle.
Press them again and they change to (0) - flipping the (Bit Logic)

The ASS Eliminator Modules - Installed in line with the switch, they remember the last switch position (when the truck was turned off) and when you start the truck, the aftermarket module pulses the switch to ground (if needed)

If you had the ASS (Disabled) Last drive - at next ignition cycle it pulses the switch to ground for you to satisfy the can bus logic.

If you had the ASS (Enabled) Last drive - then the module does not send a pulse to ground

Think of it as - The George Jetson - Button Presser

What manual are you referencing and do you have a link? It is not in the Owners Manual; at least not in the section regarding "changing the battery".

I'll have to assume your canbus/bms memory situation has to be it. Nothing strictly documented makes sense behavior-wise.

I did try pressing the off button in hopes that some previous owner installed an eliminator.