Well this is fascinating to say the least!

I created a new thread so the solution wouldn’t just get lost in old posts. See earlier under ABS Blues and Snap on MT2500 OBDII connection cable.

I’ve been wrestling with the ABS light since October with little success. Bought a snap on scanner and corresponding manual, Jeep FSM, new multi meter, spend hours looking for a new HCU pump (which no one makes anymore), dealer pulled the DTC and said the valves were sticking, bought a junk yard one to overhaul, local garages can’t / won’t guarantee that their scanner will “communicate” or work to bleed ABS brakes, new scanners wont work on 96 year model, etc, . . . .

The snap on scanner still isn’t “communicating” with the Jeep, but (can I have a drum roll please?) the light has gone out! Apparently when I checked the fuses initially, I was just looking for continuity and voltage. Turns out the 30 amp fuse ( when measured for voltage on BOTH sides of the fuse) was showing 11.78 on one side but 7.49 on the other. Swapped it temporarily with another and presto, the light went out. A friends scanner said no DTC codes are stored.

The FSM says that the ABS processor conducts its own internal diagnosis whenever you start the motor and illuminates the light if the system isn’t functioning properly.

Phew, what a PITA!

 

Apparently I celebrated too soon!

So now the ABS light comes on when the engine is started, goes off for about 30 seconds, and then comes back on to stay. The windshield wipers have now also quit. I ran the flashy code onboard diagnostic system and it didn’t show any codes. The OBD II system and the Snap-on MT2500 are now communicating on a limited basis in the codes function, but still NOT for the ABS purge function. Still says "no communication".
My GUESS is that now that I have power, the ABS processor is running its diagnostic program and finding another fault(s) which were not apparent earlier. I’m thinking I need to go back back to the drawing board, look at the wiring diagrams, and start from the beginning AGAIN.

Also thinking of bleeding the brakes (AGAIN).

Heaven forbid this should be easy!Any magical spells, ethereal revelations, clairvoyant observations, mystical suggestions, voodoo incantations, or ??? will be greatly appreciated.

goodyoleboy

 

All ABS diagnostics will tell you is which sensor needs replacing (9 times out of 10) - & I've never known it be anything else. Rather than all the grief you seem to have had, I think I'd just have replaced all of them & had done with it.

 

Thank you so much for your suggestion. I also wanted to ask about it.


 

Well, . . . the first thing I did was to replace all the wheel speed sensors so , even though the tone rings looked undamaged after I cleaned them up with a wire wheel and brake clean, I'm also recalling that one sensor was mildly degraded ( from making contact with the tone ring ? ). So I'm going to start by reinspecting the tone rings and check the clearance (.39 - .57per FSM) between the tone ring and the sensor.

In the interim, the Snap-on MT2500 has decided to cooperate after switching cartridges. After I ran the ABS simulated stop and brake bleed functions (which cleared 7 HCU related hydraulic codes), "only" (oh yeah, right, just give it time ! ) two codes remain:



1: 43 Right Rear sensor speed comparison
2: 25 Main Power circuit failure.

I think I'll bleed the brakes again just to be sure.

Since the processor was able to transmit the deficiencies, I'm inclined to think that it's not the ABS processor.

I've already replaced both relays, so I'm back to checking fuses and voltage before and after the fuses in the PDC, cleaning contacts in the PDC with electronics spray and Q-tips, and continuity in the speed sensor(s) / connections / wiring .

Snap-on says they can't / won't help me with deciphering the code(s) since they no longer support the equipment. Sure would be nice to find a list or legend for all the codes and their meaning (like what does " comparison" above mean?) .

I'm wondering whether the ## text codes format (i.e. 43 RR speed sensor comparison) as opposed to the DTC P-1234 are a creation of Snap-on, Jeep, or generic ?

As always, any revelation, inspirations, epiphanies, magic spells or incantations will be greatly appreciated.

goodyoleboy

 

Singularly unimpressed with Snap-on's attitude. One reason for buying quality kit is that it lasts, which means there's always a lot of older stuff out there in regular use which a responsible manufacturer is reasonably expected to support.

Perhaps best to stick to their handtools & leave the diagnostics to the experts in that, rather different, field.

 

Me too!

They have yet to send me an electronic copy of the instruction manual as promised.

I tried to find a new scanner, but establishing connectivity is sketchy at best and many are not backward compatible to 96 despite the OBDII connector.

$300 plus later for cables, keys, connectors, adapters, pamphlets, etc (via e-bay) , the only source I've been able to find for hints so far is youtube. Other than that' it's just Columbus Method (discover and land upon) and learn by doing. Good luck with that!

More to come.

goodoleboy

 

The second one might just be from the power cycle? Probably not a brake bleeding issue if it's complaining about a sensor. Sounds like you need to inspect the right rear sensor and the wiring to it.

 

Details, details, they'll get you every time!

So I was looking at the FSM ( Brakes 5-38 &39 ) last night and guess what? It has two procedures for installing the sensors depending on whether you're installing new or reinstalling used ones.

It appears that once upon a time the sensors were manufactured with a sticky cardboard coating on the contact face (which I'm guessing is/was 057 thick) and installed to butt up to the tone ring. The tone ring would scrape away some minuscule amount during its initial use. Only reinstalling used ones requires setting the .036-.057 air gap. I don't recall any instructions to that effect coming with the replacement parts months ago, but I do remember setting that gap. So I'm GUESSING ( if the replacements came with the sticky cardboard coating, TBD) there MAY be twice the required gap ( .072 - .114 or ???).

So I'm hoping that my reinspecting the tone rings and checking / resetting the clearance between the tone ring and the sensor MAY solve the problem. If not, I'll move on / back to the wiring.

I don't expect enough time available to investigate before I am gone for two weeks, but I'll get back with the results when I can.

Wish me luck!


goodoleboy

 

Well, . . . I couldn't stand having it hanging over my head for the next two weeks so I pulled the rear wheels and sure enough the gap was WAAAAY over the .036 -.057 from the FSM. Reset them at .045, cleared the codes, and the first one (43 Right Rear sensor speed comparison) went away (YAAAY!), but the second (25 Main Power Relay circuit failure) is still there and the ABS light now stays on all the time. I already replaced both relays so not quite sure where to start. Pull the relay(s), check voltage on both sides, and / or ??? I guess I'm a bit afraid that whatever is causing this new(er) code will create other addl problems TBD.

lawsoncl (above) : Can you please elaborate on "The second one might just be from the power cycle?"

As always, any revelations, inspirations, epiphanies, magic spells or incantations will be greatly appreciated.

goodoleboy

 

Was thinking perhaps it was the ECM equivalent code of "power was lost" from unhooking the battery.

 

I ran the flashy code and just got the standard 12 & 55. I suppose I could get ANOTHER main relay (since I already replaced BOTH earlier in the episode), but I can't help but wonder what caused the replacement to fail and what's to prevent a new one from failing again?

I guess I'll take the FSM with me while away to cure insomnia.

As always, any revelations, inspirations, epiphanies, magic spells or voodoo incantations will be greatly appreciated.

goodoleboy