Keeps shutting down

2003 CADILLAC CTS
150,000 MILES • 3.2L • V6
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GELOSRAYADO
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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?
Jan 13, 2020 at 10:54 AM
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KASEKENNY
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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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Jan 14, 2020 at 3:01 PM
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GELOSRAYADO
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I had already checked it for codes and nothing comes back. is the PCM? the ECU?
Jan 14, 2020 at 3:52 PM
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KASEKENNY
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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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Jan 14, 2020 at 4:28 PM
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GELOSRAYADO
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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.
Jan 14, 2020 at 5:28 PM
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GELOSRAYADO
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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.
Jan 14, 2020 at 5:36 PM
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KASEKENNY
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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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Jan 15, 2020 at 5:34 PM
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GELOSRAYADO
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I will have it checked tomorrow and give you an update.
Jan 15, 2020 at 6:53 PM
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KASEKENNY
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Sounds great. Please let us know what you find. Thanks
Jan 16, 2020 at 6:47 PM
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GELOSRAYADO
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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
Jan 24, 2020 at 7:03 PM
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KASEKENNY
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That is great news. Thanks for the update. Please come back to 2CarPros if you have issues in the future. Thanks
Jan 25, 2020 at 3:46 PM