Auto start/Stop Stopped working

[BMWR1200c]

2020 SEL with 33k miles purchased in July. Auto start/stop stopped working. Is 66% battery SOC probably the reason? No DTC found in FORScan. All switches set properly to on. BCM reset done with no change.

 

Edited September 12 by BMWR1200c

[Wubster100]

In the IPC, if you go to the fuel economy section it will tell you why auto start stop is off. I have a 2021 with 68k miles, and my auto start stop hasn’t worked for a while. I always get the message “engine on due to battery charging”. I will have to check my BAT_ST_CHRG % to see what mine says. After going on the highway for 8 hours, my auto start stop worked again for a few days, then it went back to not working. Technically you are only supposed to reset the BMS when the battery gets replaced. I reset my BMS anyway without replacing the battery and it didn’t seem to have an effect. I don’t think it will matter anyway because if the car is locked and it goes to sleep for a while, the BMS will relearn on its own.

[BMWR1200c]

I changed my fuel economy display on the IPC with FORScan when I first got the car to this, so I don't see the messages like you do.

 

 

 

[TourGuide]

A number of people have reported here that auto stop will quit working in that range but the vehicle starts and runs fine.  When mine reached ~390 CCA I replaced the battery and all the function returned - including the controversial auto/start-stop.

Edited September 12 by TourGuide

[Wubster100]

1 hour ago, BMWR1200c said:

I changed my fuel economy display on the IPC with FORScan when I first got the car to this, so I don't see the messages like you do.

You might need to scroll through the up and down arrows until you can find the auto start stop screen. If I remember correctly it will say “engine on normal operation” when driving. It will also include messages like auto start stop disabled due to steering maneuver.

[Haz]

From the 2020 Workshop Manual...

 

Placing your device cursor over underlined acronyms may yield popup full-words descriptions of the acronyms.

 

 

Auto-Start-Stop System

The Auto-start-stop system helps reduce fuel consumption by automatically shutting off the vehicle’s engine while the vehicle is at a complete stop and restarting the engine when the brake pedal is released. The system can be disabled through the auto-start-stop control switch on the instrument panel centerstack. The Auto-start-stop system is automatically enabled whenever the ignition is turned on.

 

The engine automatically restarts when:

• the brake pedal is released.
• the Auto-start-stop system is disabled through the auto-start-stop control switch on the instrument panel centerstack.
• the battery has a low state of charge.
• it is necessary to maintain interior comfort.
• the blower fan speed is increased or the climate control temperature is changed.
• an electrical accessory is turned on or plugged in.
• there is low brake vacuum.

The Auto-start-stop system may not turn the engine off under these conditions:

• the HVAC system is in A/C, heat or defrost modes.
• the rear defroster is on.
• the battery has a low state of charge.
• the battery temperature is below 5°C (41°F) or above 60°C (140°F).
• the engine temperature is below 46°C (115°F).
• the engine temperature is below 60°C (140°F) and the HVAC system is in heat mode.
• the gear selector is not in Drive or Sport Mode.
• the steering wheel is turned rapidly or is at a sharp angle.
• vehicle speed of greater than 4 km/h (2.5 mph) for more than 2 seconds has not occurred.
• the vehicle is on a steep road grade.
• elevation is approximately above 3,048 meters (10,000 feet).

 

Electrical Energy Management System

This vehicle is equipped with an Electrical Energy Management system which manages battery charging and monitors the battery state of charge. The Electrical Energy Management system also utilizes a load shed strategy to help control discharge of the battery and prevent, when possible, an excessively low battery state of charge. The BCM uses a battery monitoring sensor to monitor the battery state of charge.

 

To maintain correct operation of the load shed system, any electrical devices or equipment must be grounded to the chassis ground and not the negative battery terminal.

A connection to the negative battery terminal causes an inaccurate measurement of the battery state of charge and incorrect load shed system operation due to the current being used bypassing the battery monitoring sensor. Refer to the Battery Monitoring Sensor component description in this section.

 

Battery State of Charge

The Electrical Energy Management system monitors the battery current flow and voltage to determine the battery state of charge. During the drive cycle the Electrical Energy Management system software monitors the charge and discharge current and increases the state of charge during charging, and decreasing it during discharge.

 

During rest periods (key off with no electrical loads) when the vehicle enters sleep mode, the battery voltage is sampled to calibrate the state of charge. The sensor automatically executes this calibration anytime the vehicle enters sleep mode and when the total vehicle current draw is below 300mA. It takes 4 to 6 hours in the sleep mode to calibrate the battery state of charge to high accuracy. If the system draw does not allow the battery state of charge calibration over the previous 7 to 10 days the state of charge quality factor changes to flag this and some Electrical Energy Management system functions, which rely on the accuracy of the battery state of charge, may be temporarily turned off until a calibration takes place.

 

NOTE: Any devices left attached to the power socket that draw in excess of 200mA (or less depending on other battery loads), prevents a battery monitoring sensor from calibrating the battery state of charge.

 

Battery Monitoring Sensor

NOTICE: Unless the battery is being replaced, DO NOT reset the battery monitoring system using the diagnostic scan tool. This reset is reserved for new battery installation only. This reset will clear the learned battery data, the battery time in service, and will affect the aging algorithm parameters, which have been learned since the installation of the battery.

 

The battery monitoring sensor is integrated with the negative battery terminal clamp and cable assembly, which provides a ground to the sensor. The battery monitoring sensor measures voltage, current, and temperature of the battery and uses these inputs to calculate the battery condition. The sensor transmits this information through the LIN circuit to the BCM . The battery monitoring sensor has a 2-pin connector providing battery voltage and LIN connections.

 

The battery monitoring sensor is an input to the Electrical Energy Management system software. If the sensor malfunctions due to wiring issues or failure, a DTC sets. In most cases the Electrical Energy Management system functions are turned off until the sensor operation is restored.

 

 

Attached below as PDF documents are Workshop Manual sections from which the above information was obtained, along with a section on Battery Load Shed strategies, which are based upon State of Charge (SOC) conditions.

 

Good luck!

 

Starting System - System Operation and Component Description - 2020 Edge Workshop Manual.pdf Charging System - 2.0L EcoBoost - System Operation and Component Description - 2020 Edge Workshop Manual.pdf Battery Load Shed - Operation and Description - 2020 Edge Workshop Manual.pdf

[BMWR1200c]

After driving all day, battery SOC is up to 70% and auto stop/start just started working again. Wasn't earlier at 66%. Guess 70% is the threshold.

[Cerberus]

3 hours ago, BMWR1200c said:

After driving all day, battery SOC is up to 70% and auto stop/start just started working again. Wasn't earlier at 66%. Guess 70% is the threshold.

if driving all day only gets the battery to 70%, i'd be checking alternator current output. and crank on every single power hungry accessory immediately after start up while watching the output, see if it hits a threshold below its actual spec.

 

otherwise its possible the battery is just tired.

[BMWR1200c]

I'm gonna let the dealer figure it out. That's what the extended warranty is for. But at least I have a diagnostic clue before they get their hands on it.

[Wubster100]

Good idea if you are still under warranty!

[BMWR1200c]

Dealer tested 4 year old battery that came with my used 2020 SEL which I purchased in July. Tech agreed battery was toast. No charge for diagnostic. No charge for new battery installation. Charged me $10 over list for a new battery with a 3 year warranty. Reset BMS. All is good.

Got home and disabled Auto start/stop with ForScan. Life moves on......

[garycrist]

Thank you @BMWR1200c for the problem and it's solution! It will help

others in the future..🙂

[Wubster100]

Thanks for sharing the solution @BMWR1200c. When you disable auto start stop with FORScan, doesn’t this also mean that the BMS is disabled, too? Could the BMS being disabled shorten the lifespan of the battery?

[BMWR1200c]

From what I've read, I'm not 100% sure the BMS is disabled but the risk was only the potential of over charging the battery when the BMS was disabled. I'll monitor the battery SOC over time and see if there's been any bad effects but I don't expect to have any problems. There is supposed to be a PCM module to turn off AS/S. I might look into that.

Edited Saturday at 03:01 PM by BMWR1200c

[BMWR1200c]

So better safe than sorry. Turned Auto S/S back on in ForScan and will manually shut it as needed. Probably better leaving BMS on so I don's screw anything else up.