98 379 oil and air buzzer staying on with key off

Discussion in 'Peterbilt Forum' started by project359, Mar 30, 2020.

  1. project359

    project359 Bobtail Member

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    Oct 21, 2019
    Spotswood,NJ
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    Whats up guys . Looking for some help with an issue my dad is having in his 98 379. He came out one morning to the low oil n air buzzers going off without the key in. He was able to turn the blower motor on for heat also without putting the key in or on acc and it sound like a static speaker but it did work. He recently changed the actual key switch so he changed it again with no luck. He open the R/S dash to change a couple air lines and with pushing some wires around it had stopped for a couple days then started back up. He changed the ignition relay then nothing worked on the dash at all but he was able to jump the relay at start the truck so he put the old one back in.With the old relay in and the buzzers going off if he taps the relay it goes off but slowly comes back on like it has a weak spring inside or its getting power from somewhere. Im going down to see him tomorrow and I will get a better idea of whats going on and some pics .

    Has anyone had anything like this before? Ive seen a few posts about the air psi on the floor , which was recently changed also, and a few other mentions of possible loose ground wires. Just thought I would post something up to see if I get an response before I get down there.

    Thanks in advance.
     
  2. Old Man

    Old Man Road Train Member

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    Oklahoma City, OK
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    It’s the big relay behind the left dash panel. There is a big one with a small on back to back. The small one closes the big one powered the dash , ac fan ,wipers. It is not opening completely when key is off.
    Replace both of them, not easy but I’ve done it twice, the skin will grow back on your hands.
    Usually when it fails truck won’t start.
     
  3. project359

    project359 Bobtail Member

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    Oct 21, 2019
    Spotswood,NJ
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    Thanks for the info ! ill check it out later today and let you know how it went.
     
  4. 062

    062 Road Train Member

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    Make sure you’re sitting down when you hear the price. They were about $100 two years ago.
     
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  5. project359

    project359 Bobtail Member

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    Oct 21, 2019
    Spotswood,NJ
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    $100 is still cheaper then a tow to a repair facility , which you know will happen on a holiday weekend...
     
  6. project359

    project359 Bobtail Member

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    Oct 21, 2019
    Spotswood,NJ
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    Heres a couple pics of the relay changed. The second box mentioned was changed last year.

    With the old relay in , when the truck is shut off with key out the warning buzzers stay on ,tap the relay and they shut off. Replace the relay and the truck starts fine but then there is no dash at all. No buzzers or gauges, backlights for the dash but if that new relay is jumped big post to big post all the dash comes back on and works fine.

    With the old relay in and check the power with a test light one side is constant hot , as should be, and the other side slowly gets brighter until full bright with the key off which then causes the buzzers to come on.
     

    Attached Files:

  7. Old Man

    Old Man Road Train Member

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    Oklahoma City, OK
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    Best tool is a stubby Phillips, one that you ban turn with a ratchet is best. if your going to spend the time to do , Change both relays. One of mine had water in it from a leaking windshield.
     
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  8. project359

    project359 Bobtail Member

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    Oct 21, 2019
    Spotswood,NJ
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    Changed both and it still does the same thing.
     
  9. mslashbar

    mslashbar Medium Load Member

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    Jul 22, 2009
    elizabeth,co
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    Sounds like it could be your ignition switch. Take a test light and see if it's shutting off power with the key off.
     
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  10. project359

    project359 Bobtail Member

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    Oct 21, 2019
    Spotswood,NJ
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    Soooo.....Figured out what was going on. After looking at the truck and seeing what was happening it didn't make sense. With the old relay in place everything worked fine with the dash . Turn the key off and pull it out and the buzzer(s) would stay on . Had power going everywhere it should as if the key was on. Put the new relay in , that my dad pick up directly from "Peterbilt parts dept" and the truck would start but dash would not come on unless you jump the 2 big posts on the relay. I found it odd as if the relay wasn't getting the signal to close. I looked at the old relay and noticed it has 2 posts on the closing side and the one the dealer had given him was only 1. He had given them the VIN and they swore up n down it was correct. Original p/n was Bosch 0 332 002 150 , New from the dealer we were given Bosch 0 332 002 156.

    Moral of the story , ensure the part numbers are correct even from the dealer. If its a superseded # find out why it was updated.Parts can physically look the same but internals completely different.

    Thanks for all the help .
     

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