Testing of the caliper was inconclusive so I ordered a new caliper and hose. They should be here in time for me to install them this weekend. Then we'll see if that solves the problem.

 

The new caliper and hose arrived today and I installed them this evening. The clock starts now to see if that solves the Three Amigos problem. As before, I'll drive the truck more often for a month or so and report back if it passes the test; sooner if it does not.

 

Okay boys and girls, this is now even more confusing. Buckle your sea belts; this is a long post.

After replacing the RR brake hose and caliper all was good for the first 1½, ~30 mile roundtrips from home. But on the way home on the second trip the Three Amigos chimed in again. This time, however, the codes were again not helpful. In a series of cycles since then the codes have been individually and in various combinations 048, 068 and 088, each of which says Unknown Fault Code. Again, not helpful.

Looking back at posts 20 and 21 of this thread when I initially encountered 068: Unknown Fault Code, the problem turned out to be that my needle-nose pliers “crimp” of one of the new, waterproof connectors I installed had failed. I believed my re-do of that connector was sound, but to try to eliminate my installation of the connectors as the problem I bought the proper crimping tool and installed two new connectors. Same problem. Unknown Fault Code.

In the earlier case before re-doing the connector, the fault appeared immediately during the system self test at start up. Now, the Three Amigos and the unknown fault codes pop up after the truck is rolling only 100-200 ft. I tested resistance and the sensor reads 978 ohms from pins 3 and 4 of connector C0392 in the engine compartment under the coolant reservoir (spec is 950-1100 ohms). What gives?

The fact that the Amigos don’t appear immediately when the truck is started indicates the SLABS is sensing the correct resistance during the self test. The fact that they come on in the first 100-200 feet suggests to me that the SLABS is not getting the signal(s) it’s looking for when the truck is rolling.

With that in mind I decided to check the sensor itself. I pulled the wheel and the brakes to inspect the sensor. It was fully seated, as expected, but when I removed it from the hub I found what appeared to be marks on the magnet end that looked like it’s been making contact with the reluctor ring. You can see it in the picture; it’s the one on the bottom, the old sensor is the one above it.

I next tried to compare the length of the two sensors. Sure enough, the new sensor was slightly longer than the old one. I remembered seeing a thread here where someone else had that problem and shimmed the sensor. (EDIT - Turns out it was Offroad France in post #3 of this thread.) I went looking in my shop and found one, just one, very thin nylon washer that I was able to ream out to fit well on the sensor. The thickness of the washer was very, very close to the amount by which the new sensor was longer than the old one. Worth a shot, right? Well, the short answer is that I again got the same 088: Unknown Fault Code within the first 200 feet.

As I wrote above, the fact that the system passes the self test at start up but a fault is triggered so quickly after starting to drive seems like a clue. Maybe it’s time to throw in the towel and replace the hub, but as I wrote several weeks ago there was no sign of movement when I tested the hub.

Do these new facts trigger any new ideas from any of you? Thanks.

 

I've always read that wheel sensors should be replaced as part of whatever unit they're seated in -- in this case, the rear hub. I would guess that's because they're finicky little creatures and factory assembly is more reliable than trying to do it yourself. I did a front hub on my old truck because I had a persistent "rough road sensor implausible" error even though, like you, I couldn't detect any stray movement in the hub. Took about an hour and the hub cost less than $50, and all issues related to that error went away immediately.
I just replaced a rear hub on my new truck. Again, about an hour and about $50. It really does seem to be the easiest, simplest way to take care of wheel sensor problems.

On a slightly related note, I also just replaced all four sets of pads and rotors on my '03. Now, I've done brakes on a lot of different cars, trucks, and bikes, and I've never seen anything as miserably rusted and mistreated as these things. The previous owner must have been grinding away without any friction material on the pads for at least a thousand miles. There were split boots and air in the lines and the fluid was black and full of sediment. But every one of the calipers and pistons moved smoothly and easily. I have never experienced anything like it.

 

You need to find someone with a diagnostic tool that can monitor wheel sensers in real time. Actually, we have WABCO (Westinghouse Air Brake Company...for those that were wondering what WABCO stood for, acually, they were the ones that invented air brake systems for the railroad industry...no more turning the big freak'n wheel to get them to stop...lol) software at work...and l've never thought of seeing if it works on rover systems...or not.

If you have no diagnostic tools available...your only choice is to keep replacing parts.

​​​​​​​ Brian.

 

Here'’s what I think is the wrap-up to my year-long RR wheel speed sensor saga.

In the end it appears the original problem was with the sensor connector mounted on the frame next to the RR wheel, followed by a problem with the new sensor I bought.

To recap, I was getting an “87 - Rear Right sensor, Signal erratic, Intermittent” code. Thinking the simplest thing to do was to buy a new sensor and plug it in to replace the old one that’s what I did. But … the Amigos returned. Thinking that indicated a problem with the connector I cut out and replaced both the harness-side connector and the sensor-side connector. The Amigos returned. That’s when, after further inspection, I found that the new sensor was longer than the original sensor and seemed to be rubbing on the reluctor ring inside the hub. I tried shimming the new sensor to restore the air gap to the appropriate distance but that didn’t work either.

My last-ditch effort before replacing the hub and sensor together was to splice the original sensor back into the new(er) wiring and connectors setup. I did that three days ago, and since then I’ve driven the truck 100+ miles and ~20 drive cycles without the Amigos returning. I’m declaring victory.

 

 

This thread has been so helpful! How do you know the correct depth of the sensor once installed? Mine came with a stack of shims. I have low voltage thinking this is a possible cause, would love know how to measure and add shims as needed.

 

I don't have any specs to offer. All I can suggest is to perhaps try to measure the depth of the hole from the surface where the sensor mounts to the surface of the reluctor ring, and then back off a millimeter or so. I don't know whether or not the correct gap is specified in the RAVE.