ABS diagnosis & repair in a Gen II

So, following a little mishap, my Gen II which I've owned from new had amongst other things a new short side drive shaft. Following various repairs to get it back on the road, the VSC began to play up - activating when braking in a straight line on a good surface. Well, the subframe had been off & the nearside front brake line drained, so the braking system was bled up again throughout (no issues & no air bubbles found). The power steering was re-initialized (again) and the ABS was cleared down & re-initialized (again) - no progress, the behaviour remained exactly the same.

Now, we had code C0205, nearside front wheel speed sensor and poor VCS behaviour, so we went for a drive with the techstream connected, monitoring all 4 wheel speeds. This logged intermittant speed drops on the nearside front, showing that the speed sensor was upsetting the ABS - very interesting and semi regular. I don't know how the skid control ECU's counting strategy works, so I don't know how significant a missed pulse is, but I suspect the vehicle speed interacts with the counting strategy for one or more missing pulses to produce the semi - regular speed reductions we were seeing.

Now, I am in the fortunate position of owning two 2005 UK spec Gen IIs, so, as a code C0205 was being thrown & as it was the easiest place to start, the nearside front wheel speed sensors were swapped - and worked absolutely fine in the other car. In the unhappy car, the problem continued, so it wasn't that.

Next challenge was to swap the skid control ECUs - next easiest. I can confirm that it is possible to remove the skid control ECU from a UK spec Prius without dismantling the entire dash, but it is quite awkward. The skid control ECU has the knobbly heatsink facing outwards and is on the side of the car, by the drivers right leg. The kick plate & lower trim need to be removed from the drivers side, the a large connection & fuse box needs to be disconnected, unbolted & removed out of the way. This created enough access to get a hand up inside the dash to unbolt the skid control ECU, though it was very awkward! This was then plugged into the other car without removing anything, just turning the connectors back on themselves... where it worked fine.

Two components were left in this problem, the wiring loom (no evident damage and very awkward to swap) and the reluctor ring on the new half shaft. The ring was inspected through the wheel speed sensor hole, with no fault found.

The wheel speed sensor was replaced & a borrowed oscilloscope was hooked up to the wheel speed sensor & with the car on axle stands, the engine was allowed to rotate the hub. This showed one small pulse, in amongst all of the standard size pulses, indicating a defective reluctor. The reluctor ring was inspected again, via the ABS speed sensor hole, and it was just about apparant that one of the teeth appeared to be compressed. The knuckle was removed, making it far more obvious that one of the teeth was flatter than it should be, accounting for the small pulse. Very difficult to see looking down from the top. On reflection, I think it is a manufacturing defect.

An outer CV joint kit was bought from eBay as this includes the reluctor ring - at time of writing I have been completely unable to separate the outer CV joint. Having removed the half shaft from the car (a fight in itself) and hit it a lot on the bench, with heating & cooling, I can't see how it comes off without cutting & guess it must be pressed into place? Either way, I don't think it's coming apart without major damage, so I'll be replacing the half shaft again. This time, checking very carefully for any damaged teeth on the reluctor ring!

Thanks for reading

Matt

 

Hi Patrick,
The replacement half shaft was an aftermarket part. Given the price advantage, the second replacement will be aftermarket as well, but I will be checking the reluctor ring carefully before installation. The other teeth look okay & the oscilloscope is producing the right output for the rest of the ring, so I would expect a second half shaft to be okay... if not, it will be going back without being installed!

 

So, today it was time to fit the replacement half shaft. This one also had some very minor damage to the reluctor ring - it was inspected very closely & looked like it had been bashed in the post. I felt it was too minor to affect performance & decided to fit it & see what happened.

The new oil seal went in without any issues, remembering not to drive it all the way down the bore. Drive shaft in, knuckle & sub frame back on, steering re-assembled.

The ATF was re-used. It had been in for around 1000 miles, so no real issue. It was strained through a paper filter with very little debris caught for a high mileage transmission. You can see from the bowl just how much ATF is actually within the transmission.

Running the car on axle stands - no issues at all. With the near side front (the problem corner) spinning & the off side front blocked, the car measured speed no problem. Taking it for a test drive, the VSC now behaved properly and braking performance was back to normal.

All in, an interesting little job. Moral of the story - check eBay spares very carefully before fitting!

Thanks for reading

Matt

 

For a final update, a few people have tried removing outer CV joints. Today I decided to break down the outer CV joint to see what was inside... after all, I couldn't get it off of the end of the shaft, despite a lot of hammering.

The results... to remove, I had a cut away the outer ring with an angle grinder, snap off & remove with a club hammer. The inner part still wouldn't budge with a hammer, so it was carefully slit until just short of the splined shaft with an angle grinder and then cracked off with a hammer...

And inside, it was a splined shaft and a circlip - just not one which wants to come out!