Grounded +12V From PCM - Cascading Things Not Working

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muttleytm
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Joined: Thu Feb 04, 2016 1:59 pm

Grounded +12V From PCM - Cascading Things Not Working

Post by muttleytm »

I was putting a receiver in and out a few times on another issue. A number of wires for other things got disconnected. One of them was the +12V wire from the PCM that powered and turned on and signaled the receiver that the car was in reverse so it switched the screen to display the image from the camera. As I was putting things back together I saw the wire from the PCM and wasn't thinking and saw another short wire with a mating terminal and I attached it. When I started the car the receiver fired up. When I put the car into reverse the screen was simply black. I also noticed other things weren't working. The blower motor for the AC (it is pretty hot out), the windows, the dash display, the inside power door locks, the turn signals and probably the rear lights.

I looked around and it sounded like it might be the "tail" fuse in the inside fuse box or the dome fuse. I checked both and both are good.

It is hot and the inside fuse box is hard to see and get at. Besides the heat my back and knee are in need of repair at the moment. I'd like to try doing something other than testing all of them.

I can't find a fuse for the PCM mentioned anywhere.

Anyone have any ideas?
muttleytm
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Joined: Thu Feb 04, 2016 1:59 pm

Re: Grounded +12V From PCM - Cascading Things Not Working

Post by muttleytm »

A couple things, a detail and maybe a clue or simply a coincidence:

The car is a 2003 Vibe.

This evening I checked and I did have at least the top tail lights lit up when it was running and I turned on the headlights. I checked and I did have at least the top tail lights lit up. I noticed that when I touched the brake I'd hear a click from the console area, probably somewhere below the radio. I had the headlights on at the time and I would see they would dim when I pressed on the brake. I'm assuming the click is the brake light relay.

I went to a gas station and pulled into a spot in front of a big window. The headlights looked dim. I shut the car off and later thought to back in so I could check to see if the brake lights lit in the window as well. When I went to start it the started and the motor turned the engine a little, but not fast enough to get it to start.

Whether this has anything to do with the reverse wire getting grounded or not I'm not so sure. It has been hot. It is a new car to me, but used. I don't know anything about the battery other than it got the car started fine. I have found though that while cars sometimes have trouble cranking when it is very cold, when the batteries actually fail is usually when it is very hot.

I was about ready to post this, but decided to check where the brake light relay is and found this, so here are a few hints for me tomorrow or when I get the time to take a look. I have a Dr appointment and then if no solution will have to call tow truck to get the car home and out of the station.

In any event or for posterity here is what I just found:

Mike Humes Apr 07, 2019
I have no rear tail lights or brake lights or dome light no cruse control vibe 2003. I do have front parking lights and the dash board light dimmer works fine. All fuse's are fine. what do you suggest
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hooftey01
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Electrical problems can be very complicated you may want to take it to a shop that is equip to deal with these issues.

Posted on Apr 07, 2019

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montehammons
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Pontiac Master
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The tail lights work off the headlight switch, and there is a fuse for the tail lights. Make sure the fuse is good, first, a 15 amp (blue) fuse in the instrument panel fuse block. Then, you might have a bad headlight switch.
So you DO have dash lights, they just don't dim from the dimmer switch? In the wiring diagram, there is a green wire from a "tail light relay" (in the "Junction Block-Right Instrument Panel") that carries power to all the exterior lamps, as well as having a splice to the Instrument Panel Cluster (illum. bulbs), and to the lamp dimmer, and to the radio bulb.
To do any further testing, you would need a voltmeter or a test light, so you could chase down this power loss. Good luck.

Posted on Oct 17, 2016
muttleytm
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Re: Grounded +12V From PCM - Cascading Things Not Working

Post by muttleytm »

I guess I got it all figured out.

The battery going bad was just a coincidence. I measured the voltage and it was 11.8 which most likely means a bad cell. I replaced it and all is well.

I also used the suggestions I posted from elsewhere. The dome light did work as did the rear tail lights, the brake lights, the headlights and the front running lights. I checked the 10A Gauge fuse and it was blown. I replaced it and the windows, AC, etc all worked.

Initially I thought that the fuse that blew would be upstream of the PCM since that is where the +12V I grounded came from. I realized later that the PCM is just a microprocessor or two activating some relays, solid state relays or transistors. Usually the relays and such that are activated by microprocessors are optically isolated so I imagine that is the case with these. There are a lot of wires connected to the PCM. One of them would be coming from the Gauge fused circuit.

So I think all is well. Thought I'd just post if for the record. Maybe someone can get something from it.
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joatmon
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Re: Grounded +12V From PCM - Cascading Things Not Working

Post by joatmon »

Glad you got it figured out and that it was only a fuse.

Sorry to not have helped. I was remote and away from my reference material.

So. How does the new receiver sound?
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muttleytm
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Re: Grounded +12V From PCM - Cascading Things Not Working

Post by muttleytm »

The receiver works fine, but had less power than the stock radio. It would clip on certain songs with a lot of bass. ( could also hear some higher pitched ringing, but between allergies and ear wax I had ringing all the time. Got the ears cleaned. I was taking the radio in and out because I was installing an amp behind it. That's when the wires got pulled out and I reconnected them wrong.

I still haven't got the amp working or getting any sound out of them. At first there was a bad wiring harness for the amp and lots or issues getting with customer service/tech support. They did send a new harness. I can sort of hear a little sound from the closest speaker when I turn the car on or off when I'm in a really quiet area. The amp has some DIP switches. The supplied diagram doesn't really correspond with the way the switch is installed. I tried a few variations but haven't found the right ones. That is what I think the issue is.

I did finally get a hold of someone who shipped me the new harness. I sent a picture of the amp and asked if they could edit my picture of supply a new photo of one set properly for what I want to do: No filters, 4 channel and low lever pre-amp RCA input. That persons passed the thread to someone else in tech support. Still waiting to hear from them. It's inconvenient but OK too, I'm very busy with other things.
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