Peterbilt 379 Wabco ABS erratic codes

Discussion in 'Peterbilt Forum' started by rellis73, Jul 18, 2021.

  1. rellis73

    rellis73 Bobtail Member

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    Jul 18, 2021
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    2006 Peterbilt 379 with an (what I believe) E series Wabco ABS controller (Peterbilt in their infinite wisdom put a piece of masking tape right over the identification label on the controller and after so many years it is impossible to remove and see the entire label). ABS dash light came on just before the truck was going to the shop anyway (IVA problem with the C15 CAT, imagine that) so I had the mechanic read the codes for me while he was plugged in. Two codes were shown, one active - left rear wheel sensor, one logged - RIGHT front modulator valve open. I thanked him and left from his shop and purchased a wheel sensor and changed it out. Next day I'm driving and shortly after leaving our shop the ABS light comes on again.strange I think to myself and continue on my day. The next morning I crank the truck, no light. Start down the road and shortly after the light comes on again. Third day, same thing. I am traveling the same route every morning and this light is coming on at exactly the same time, within feet of where it came on the previous day. Knowing that I need to get this fixed I dive into it thinking that this is not something that I really want to take to a shop because I'm thinking its something simple. First thing I do is look for the elusive blink code switch so I can get the codes from the controller. Yea, after dismantling the dash that was a no go. So I wired a switch in and the first code that comes up (logged code) is the LEFT front modulator valve (code 2-1). Odd I think since the mechanics software showed the opposite side. No worries, I remove the wiring connector from the controller and test all four modulator valve solenoids and all read 7 Ohms on both the inlet and outlet side which is within spec according to Wabco data. (I figure since I'm reading the wire to the solenoid and the solenoid itself the reading is actually slightly higher than if I read at the solenoid.) After checking all the connections I plug the connector back in and turn the key on, immediately get a solid ABS light and I check the codes. Now I'm getting all wheel sensors and all modulator valves codes 2-1 thru 2-4 and codes 4-1 thru 4-4). I attribute this to unplugging the connector. I put everything back together and proceed to drive the truck on a test drive to maybe clear that up. I start the same route that I would drive on a normal morning and at the exact same spot as before the ABS light pops on. I stop immediately to check the code and now it shows the RIGHT front modulator valve (code 2-2). I can hear the solenoids clicking when first turning the key on and have done the chuff test and all sound good (and more importantly the same) except the LEFT front. It chuffs, but sounds slightly weaker than the rest (to me). Anyone else, have any experience with such an issue of a "bouncing" code? Is there a wiring problem or maybe a chance the controller is wonky? I'm not sure what else to try and I don't want to just throw parts at it until something sticks.
     
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  3. Nss

    Nss Bobtail Member

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    Check your wiring on truck side to the controller. Both ground and power wiring.
     
  4. Nss

    Nss Bobtail Member

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    Ohm the resistance on 'christmas tree' 3 wire per spec. Have had experience with older systems ohming in spec but on high end. Then parts can be replaced because of high end of spec and does not hold a load.
     
  5. FLHT

    FLHT Medium Load Member

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    ABS Reset button ?
     
  6. rellis73

    rellis73 Bobtail Member

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    Jul 18, 2021
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    I did. Positive was showing battery voltage and ground side was showing less than 0.05 ohms resistance to chassis ground.
     
  7. rellis73

    rellis73 Bobtail Member

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    Jul 18, 2021
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    Would this be different from testing those terminals at the Walcott controller? I did check the modulator solenoids and all homed to 7 ohms. Spec is 4-9 ohms.
     
  8. rellis73

    rellis73 Bobtail Member

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    Jul 18, 2021
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    Are you thinking it’s just a stored code? I thought the same but I am unsure of a “reset” button. I did undo battery ground for several minutes and then reconnect. Light then comes on with key but goes out until truck has traveled about 10 miles. That’s the odd part, to me anyway.
     
  9. FLHT

    FLHT Medium Load Member

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    Their should be a push button in the roof of the map pocket.
    (The cubby just under the ash tray.)
    With key on push it ABS light on dash will start blinking but will not go off until you go over 10 mph.
     
  10. flood

    flood Road Train Member

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    question is. You said it always goes off at the same spot when your driving..... is their any bump at that spot... any at all...???

    Reason I ask is I just went thru this with a Ghost Error for wheel sensor on the back of my truck... rear read drive left or right and front rear drive left.. never the same 1 but always 1 of the 3. I'd get it reset and a hour or 2 days later it would do it again... finally I changed the wiring harness from the sleeper back and it's been fine...

    Checked the wiring harness and everything checks good BUT for some reason changing it fixed it...... like I said GHOST ERROR
     
  11. rellis73

    rellis73 Bobtail Member

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    Jul 18, 2021
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    Nothing at that particular spot in the road that I notice. I totally get the GHOST ERROR reference and this is why I HATE trying to chase down intermittent problems. This thing has changed sides a couple times with the error but it has always been the front axle. There is always that possibility that there is a short in that harness (those wires for the front axle run the same loom until they split for left and right side) and this is what is causing the errors. I think I said it before but I just hate the thought of throwing parts at this problem until I find one that sticks but I'm just about to that point.
     
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