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Keeps shutting down

Tiny
GELOSRAYADO
  • MEMBER
  • 2003 CADILLAC CTS
  • 3.2L
  • V6
  • 150,000 MILES
My car was working great, the key wouldn't come out of the ignition but I would just click the button on the steering wheel and it would come out without an issue. The problem I am having is that now it turns off, after like 5 -10 minutes the car's voltage goes down from 14 to 12 and it turns off, and after that I try to turn it on and it just does a clicking noise like if the battery it out. After a few cranks it comes back on. So I can't drive it that way. I can even just turn it on and leave it in park and after a few minutes it does the same thing. I have changed the crank shift sensor, the battery, the alternator. Can someone please help?
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Monday, January 13th, 2020 AT 10:54 AM

10 Replies

Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
We need to start with pulling codes. This sounds like a crankshaft sensor but since you replaced that we need to see if the computer is seeing the issue.

If there are no codes then I can only assume there is an issue with the PCM. The voltage regulator is in the alternator but the voltage is sent to the PCM and I am thinking the PCM is causing the voltage issue.

Let's start with codes and go from there. Thanks
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Tuesday, January 14th, 2020 AT 3:01 PM
Tiny
GELOSRAYADO
  • MEMBER
  • 6 POSTS
I had already checked it for codes and nothing comes back. Is the PCM? The ECU?
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Tuesday, January 14th, 2020 AT 3:52 PM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Yes. ECU or PCM or ECM are all the same thing. ECU is more general because it stands for electrical control unit so any control module can be an ECU. ECM is Engine control module and PCM is Powertrain control module.

The reason I suspect the ECM/PCM is this has the ability to shut the vehicle off and cause the issue you are seeing. It isn't supposed to shut the vehicle off but if it looses power or the crank signal it will think the engine just shut off and turn everything else off. It is supposed to perform what is called load management but this is not happening.

The only thing I am not confident about this is when you turn the key again it just clicks. This points to a wiring issue but if that is the case, with no codes, it is going to be very difficult to figure out without a little more to go on.

Do you have a scan tool that can monitor live data? If so we need to find out what the ECM is seeing on the input sensors.
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Tuesday, January 14th, 2020 AT 4:28 PM
Tiny
GELOSRAYADO
  • MEMBER
  • 6 POSTS
Sometimes it does the clicking, most of the times it turns right back on. When it does the clicking it will do it a few times then comes back on and starts like normal. When the car is on it works great but something happened and it just shuts off. When we got it scanned it didn't want to read any codes, nothing came back.
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Tuesday, January 14th, 2020 AT 5:28 PM
Tiny
GELOSRAYADO
  • MEMBER
  • 6 POSTS
During the time the car is on the voltage on the screen is at like 14.7 and I starts going down to like 13.8 and at a certain point it will drop to 12 and shuts the car off right away.
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Tuesday, January 14th, 2020 AT 5:36 PM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Okay. I am thinking this is one of two issues. First the easier of the two is the belt tensioner. I asked a GM dealer if they heard of this and they have. Apparently this issue is not that uncommon. They said that when the engine is under load coming to a stop and the tensioner is not holding proper tension on the belt that the voltage drops and once it reaches about 12.5 volts while running the PCM shuts the engine off.

Then other issue is the PCM itself. Unfortunately they didn't give any way to test this other than hooking a volt meter up to the battery when it is happening and monitoring the voltage the ECM is seeing. If it differs then the ECM is most likely the cause.
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Wednesday, January 15th, 2020 AT 5:34 PM
Tiny
GELOSRAYADO
  • MEMBER
  • 6 POSTS
I will have it checked tomorrow and give you an update.
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Wednesday, January 15th, 2020 AT 6:53 PM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Sounds great. Please let us know what you find. Thanks
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Thursday, January 16th, 2020 AT 6:47 PM
Tiny
GELOSRAYADO
  • MEMBER
  • 6 POSTS
Thank you so much Kenny, I changed the PCM and it worked, it's riding real good. I got the PCM delivered today and got the car up and running like 30 minutes ago. Thank you
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Friday, January 24th, 2020 AT 7:03 PM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
That is great news. Thanks for the update. Please come back to 2CarPros if you have issues in the future. Thanks
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Saturday, January 25th, 2020 AT 3:46 PM

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