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Engine will not turn off; it stays on after pressing the stop the button?

Tiny
CANDLQR
  • MEMBER
  • 2017 CADILLAC ATS
  • 2.0L
  • AUTOMATIC
  • 40,000 MILES
Engine stays on after pressing the stop button. The only way to make the car stop is to removethe ECM fuse.
Sunday, July 31st, 2022 AT 12:50 PM

13 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,643 POSTS
It sounds like the start stop control capacitor is bad, but we should check the fuses first, here is a guide to help you and fuse locations # 5 BCM and the MSM above the left rear fender well. You might eb able to reset the system, here is how:

Reset Criteria
The stop/start capacitor control module calculates the state of health of the stop/start capacitor and sends it to the ECM. If a bad state of health is determined, the charging and discharging of the stop/start capacitor is disabled. If the stop/start capacitor or stop/start capacitor control module is replaced, the reset procedure will need to be completed.

Reset Procedure
Note: Ensure the following conditions are met before performing the reset procedure, or the reset procedure may fail.
No DTCs are present
Battery voltage is above 11 V.
No battery charger is installed while performing the reset procedure
Note: You can only perform 1 reset per ignition cycle. If you need to perform the reset procedure again, you must shut off the vehicle and wait 3 minutes.
Ignition ON, engine OFF
Command the Stop/Start Capacitor Control State Of Health Reset with a scan tool.
Wait 2 minutes for the state of health reset procedure to complete.

If these are okay let's do a CAN scan which is easy to do, you can get a CAN scanner from Amazon for about $30.00 here is a video to show you how.

https://youtu.be/u-4syLc-ifQ

here is a scanner link

https://amzn.to/3o41KcZ

Here is the location of the start/stop capacitor module and fuse locations in the diagrams below. Check out the diagrams (below). Please let us know what you find. We are interested to see what it is.
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Monday, August 1st, 2022 AT 10:11 AM
Tiny
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  • 7 POSTS
Man, this is the most thorough and concise answer that I have ever been able to get from anyone. I truly appreciate the insight. I was able to clear the codes with the scan tool that you included in the link, but it is not bi-directional, so I couldn't perform the reset. Do you have another scan tool recommendation for the reset of the capacitator module? I want to try that as you recommended, before buying one. Thanks again so much.
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Friday, August 5th, 2022 AT 7:11 AM
Tiny
KEN L
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Yes, this one does the job and doesn't cost to much $180.00

https://amzn.to/3AaON8l

Back in the day this tool would have cost more than 5g's. Got to love technology getting more affordable, please let me know what happens, it would be great to fix this problem.
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Friday, August 5th, 2022 AT 6:09 PM
Tiny
CANDLQR
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  • 7 POSTS
I will keep you posted Man. I didn't get your reply this before I bought a scanner. See what you think about this one: https://www.amazon.com/LAUNCH-Bidirectional-Diagnostic-Calibration-Registration/dp/B09XV8VR35/ref=sr_1_2_sspa?crid=1XG6O420UCH1N&keywords=launch+obd2+bidirectional+scanner+diagnostic+tool&qid=1659790761&s=automotive&sprefix=launch+obd2+bidirectional+scanner+diagnostic+tool%2Cautomotive%2C127&sr=1-2-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUEzS0lRMk5NWEJPT1A5JmVuY3J5cHRlZElkPUEwMTM1MDM3MzRGQ0JVTEYxUTdZSSZlbmNyeXB0ZWRBZElkPUEwMDQwOTc4M0lOSkVDVzRONk1LUiZ3aWRnZXROYW1lPXNwX2F0ZiZhY3Rpb249Y2xpY2tSZWRpcmVjdCZkb05vdExvZ0NsaWNrPXRydWU=
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Saturday, August 6th, 2022 AT 6:14 AM
Tiny
KEN L
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Yep, this one will work, let me know.
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Saturday, August 6th, 2022 AT 7:43 PM
Tiny
CANDLQR
  • MEMBER
  • 7 POSTS
Here is my current status: I commanded the Start / Stop Cap to discharge, and it did not. It was at +2v when I read the voltage on the scanner and it did not change. I tried the Reset function anyway and it established communication and then displayed the reset status. I started the car, and it still would not turn off. I removed the battery cable and pulled the unit so I could make a measurement with a multimeter. Sure, enough it read +2v on the meter as well. I used a set of jumper cables to drain the voltage off by jumping the hot on the unit to chassis and for about 1 minute. I took a reading and it read 0v. I connected everything back and connected the scanner. I now commanded the unit to discharge, and it was already on 0v. I commanded the Reset and it again established communication and then displayed the reset status. I started the car and let it run for a bit at which time I turned it off and the engine still kept running. I then used the scanner to display the voltage on the start/ stop cap and it still read 0v. The same as it had when I discharged it even though the car had been running for several minutes. So, does that mean the module is bad?
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Monday, August 8th, 2022 AT 7:16 AM
Tiny
KEN L
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It sure sounds like it because it is not responding to the commands.
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Monday, August 8th, 2022 AT 6:05 PM
Tiny
CANDLQR
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Hello Ken L, I changed the module and reset the health, but I still have the same problem. The car still will not turn off. I removed the Cue, it runs, I removed the switch, it runs, I removed the battery cable it runs. I am thoroughly at a loss!
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Saturday, August 13th, 2022 AT 3:51 PM
Tiny
KEN L
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II am sorry to hear that, did you ever do the CAN scan because the only other thing I can see that would cause the problem is a bad BCM. Here is the wiring diagrams so you can see how the system works. I have also included how to change out the BCM, I assmumded you check all of the fuses with the key on correct?
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Monday, August 15th, 2022 AT 11:41 AM
Tiny
CANDLQR
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Yes sir, I checked it with the scanner, and I have reset all codes, I have pulled out the main fuse box and checked all fuses and relays in all boxes. I do have another question though. What voltage should I read on the Start / Stop capacitor when reading it on the scanner after I start the car? I am reading 0 volts the entire time. Is that normal?
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Monday, August 15th, 2022 AT 12:42 PM
Tiny
KEN L
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I don't think so, it should have voltage before you start the car.
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Tuesday, August 16th, 2022 AT 6:11 PM
Tiny
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I'm going to look around and see if I can find out what that voltage is supposed to be. I would think there would be some voltage there as well, but no idea how much.
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Wednesday, August 17th, 2022 AT 6:45 AM
Tiny
KEN L
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Please do, I want to find out what's wrong, could be a PCM updated? I checked and there is no TSB for this problem.
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Wednesday, August 17th, 2022 AT 11:40 AM

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