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Why do I have power to my ICM when the key is off and not when it is on?

Tiny
RVMAN350
  • MEMBER
  • 1998 PONTIAC GRAND PRIX
  • 3.8L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 150,000 MILES
Why does my car chime 5 or6 times every time I hook up the battery?
Monday, November 29th, 2021 AT 3:43 PM

9 Replies

Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Just trying to clarify what you are looking for. When you say the ICM has power with the key off and not on, are you referring to the ignition control module?

I attached the info below on this ICM. The ICM would have to have power when the key is on or the vehicle will not start. Is that the issue you are having?

If you are talking about something different, let me know.

Then are you asking a second question on why the car chimes when you hook the battery up?

If so, then when you are hooking the battery back up, there are modules that are going to come back on line so that may be causing the chimes, but can you get a recording of these chimes so that we can see what it is doing?

This may be related to the ICM having power when the key is off.

To address that we need to check the power on each of the terminals with the key on and off.

https://www.2carpros.com/articles/how-to-check-wiring

I attached the connector view below so let us know what the voltage is on these and we can go from there. Thanks
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Tuesday, November 30th, 2021 AT 9:23 AM
Tiny
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Hey KaseKenny1,

Let me give you some background that might help. Back on or about February 25, 2021, I asked a question on your website about ECU/PCM pin #48 I got a response from Asemaster6371. The problem I had was after hooking up the ECU/PCM I went to hook up the battery and the ins. On the red/black striped wire going to pin #48 started to melt off of the wire. I removed the ECU/PCM and the ICM and bench tested the coils on the ICM and tested the ECU/PCM they tested good. This is a project car, so I let it set. I just started to work on it again this is where I am at now. With the ECU/PCM still out of the car I checked the wire harness for the ICM. This is what I found key off pin k checked.00 ohms on cont. To the battery using pin k I checked all the wires found 11.7 volts on pin p no volts on any other pins. Using pink, I checked all the pins for cont. None found. With the key on using pink, I checked all of the pins for volts and cont. None found. As for the chiming sound I could not record it. I turned the key off and removed it the car chimed 5 times like the key was still in the ignition. Then it stopped. Hope this helps
Thanks for your help.
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Sunday, December 5th, 2021 AT 3:50 PM
Tiny
KASEKENNY
  • MECHANIC
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I just want to confirm that you did this testing with the ICM connector unplugged?

Most of these circuits are not going to produce voltage until the engine is turning.

These are called signal circuits so that means they send a signal when they are active.

So, if you have power and ground going to the ICM then we need to check these circuits when the engine is cranking, and I suspect you will get some voltage. However, you will need a labscope in order to determine if the signal is correct because the voltmeter will not be fast enough to show the proper voltage.

However, at least this will show that the ICM is getting the signals. Even if this is the case, I don't think that is the reason for the chime. If the chime happens when you hook the battery up and then stops then that is a module going through an initialization process and it completes when the chime stops.
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Sunday, December 5th, 2021 AT 6:03 PM
Tiny
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That is all good info. But my main problem is that I lose power to my ICM when the key is put in the run pos.
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Wednesday, December 8th, 2021 AT 10:06 PM
Tiny
KASEKENNY
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Okay, let me confirm what is happening when you say you are losing power because I think this means something different to me.

On pin P when you turn the key on, do you have voltage using a known good ground? Then do you have voltage in the on position on pin P when using K for a ground?

Pin P should have 12 volts when the key is in the on, start, or during the bulb test so let's start with this and then work from there.

I understand this may be duplicate info, but I am not sure I am understanding, and this is important or we are going to be going in the wrong direction. See the wiring diagram below that will help.

Thanks
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Thursday, December 9th, 2021 AT 10:51 AM
Tiny
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I have power on pin p when the key is off when I turn the key on, I lose power on pin p wtf it is completely backwards right? It is the same when I use pink, or I use battery ground.
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Thursday, December 9th, 2021 AT 12:33 PM
Tiny
KASEKENNY
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That is correct. It is completely backwards which means we most likely have the issue on the fuse block. More than likely, it is shorted or has some other issue.

Basically, I would take that wiring diagram that I attached above and remove the fuse and check the same thing there. You should have 12 volts on the battery side of the fuse only when the key is on. If you have it when it is off, then that fuse box has an issue on the circuit board.
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Thursday, December 9th, 2021 AT 3:38 PM
Tiny
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Okay, I have the under the hood fuse box on the bench. Do you have any information on how it comes apart?
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Sunday, December 12th, 2021 AT 3:22 PM
Tiny
KASEKENNY
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Unfortunately, these are considered non serviceable so that just means they don't publish any info on how to take them apart. It doesn't mean they can't be taken apart, but I just don't have any instructions on how to take it apart.

Normally there are screws or clips on the underside to get it to separate. Some of the Chrysler fuse boxes are snapped together but I am not sure of the GM.

I would suggest just doing some Google searches and see what turns up. I am sure there are some videos of similar fuse boxes being taken apart.
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Sunday, December 12th, 2021 AT 6:02 PM

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