Peterbilt 379 Wabco ABS erratic codes

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.

 

I did. Positive was showing battery voltage and ground side was showing less than 0.05 ohms resistance to chassis ground.

 

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.

 

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.

 

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.