Prius 100,000 mile maintenance

  Part 1: Overview;   tires/brakes
  Part 2: Underhood
  Part 3: Headlights: the Big Schnoz
  Part 4: Inverter pump
  Part 5: Coolant testing
  Part 5b: Engine coolant
==>   Part 6: Transaxle / driveline, references

Transaxle and driveline

It's also about time to change the transaxle fluid again, which after doing it in mine and some friends' cars has become fairly routine. [And *not* by uprooting the whole inverter like the first time at 50K -- that, as with anyone's first time for many other things, was just for exploratory and instructional value!] Toyota's listed maintenance interval says 100K on this, but the collective owner community with help from some of the used-oil analysis places agree that the original factory load doesn't really hold up nearly that long. Remember that our transaxle fluid is *in contact* with high-voltage motor windings, an environment in which suspended wear-metal particles are not particularly helpful.

But while we're messing around in the area of the transaxle, there are a couple of other things worth looking at in the process.

Just about any opportunity to dive underneath the front of the car should be used to check up on the four CV joint boots and the stainless bands holding them at each end, as continued dust-boot integrity is fairly critical to a trouble-free driveline. Any cracks/rips or leakage will lead to rapid joint degradation from dirt and loss of their lifetime load of grease inside.

Pulling any of the under-engine covers isn't necessary just to change the fluid, as it's easy to access the fill/level-check plug from underneath and get the long fill-funnel hose in there securely. But with the left fender-liner already out of the way it's easy enough to pull the cover under the transaxle side.

These three bolts in the long slot get wet a lot, and may be slightly icky to remove. Let's go slowly and try not to shear them off...

Again, watch for falling road-dirt while removing the panels. In most cars there may be an additional piece or two of plastic over this slot; the design of this area changed slightly over different model years. The bits that bridge the valley were lost on mine some time back on a little dirt-road adventure. Good thing it's all just flexible plastic.

The three bolts into the radiator-bracket *were* treated the last time they were out, and have rusted up again. So in general it's worth pulling them for another shot of anti-seize every so often anynow.

Three important connectors go into the transaxle, besides the big orange motor leads themselves. They carry the position resolver wiring for MG1 and MG2, and the thermal probes that monitor each of their stators. One of them is called "M5" in the diagrams and feeds the MG1 resolver inside, and is the leftmost one seen here.

M5 was one subject of the infamous "stalling" recall from Toyota. Back in 2005 there was a bit of a hue and cry from owners whose cars simply ceased running in the middle of traffic, primarily due to an ECU programming error. Toyota issued a reflash for the firmware to allow a little more grace time for engine starting before deciding that the engine was out to lunch and lighting up all the dashboard warning lights like a Christmas tree. It was around this time that "christmas tree" and "triangle of death" became mainstream as popular synonyms for just about any Prius failure that lit up error lights.

I never bothered taking this car in for the reflash, having never had the stalling issue. Either I already have updated ECU code [although it's beyond me how it could, as this is a mid-year '04] or my driving style so rarely puts the system into borderline timing states that the bug has never kicked in.

While the main treatment was reflashing the ECUs, some cars were also to receive another funny little fix, to open up the connections behind M5 and, as the SSC-50P memo puts it,   "...a special dielectric grease will be applied to a connector for the transaxle to prevent water intrusion."  

But to only one out of the three, which seemed really odd.

Now, all the small-signal connectors in question are on the front of the transaxle and they *all* get splashed in wet driving. However, apparently that wasn't the source of the problematic water. M5 points downward out of the transaxle, while the other two point straight forward or up, and a read through the SSC document shows the grease being applied to the *back side* of M5 which is tilted upward as it sits inside the transaxle. Thus, the water in question must fall from the inside down into the pins in the back side of the inner resolver connector.

It's hard to envision how significant water could get inside the transaxle in the first place, let alone fly around and land inside random internal parts which are all soaking in transmission fluid anyway. That has always remained one of the great unanswered Prius questions. Maybe it could come from some runoff path of internal condensation? On the other hand, it *is* right under the cover plate with the one-way air inlet valve. Who knows. Toyota evidently thinks they do, but they're not tellin'.

Anyway, having recently helped a friend debug what turned out to be a corroded connector into his truck transmission, I figured it was time to take a closer look at all this and maybe finally do the equivalent part of 50P myself if there was any hint of a problem.

The external connectors all look nice and clean as do the sockets and pins they fit to, so no problem there despite New England's best efforts to liberally salt them up for me.

Back when SSC-50P came out I had taken connector M5 out for a look, decided that it was fine, and put it back. Now, upon trying to extract it again, something feels like it's resisting removal, pulling from the other side. I *know* there's sufficient wire length inside ... finally, it comes free with a big splorchy sucking sound as the O-ring clears the housing. This tells me that the transaxle "vacuum" is still in effect, meaning all the seals at the axles and engine-shaft are still good and the little one-way air valve is doing what it's supposed to! I must have done the previous removal soon enough after opening up some other part of the transaxle, and the inside pressure hadn't yet pumped itself sufficiently negative via thermal cycling, because I don't remember any particular difficulty with it before. Some other transaxles I've opened don't retain pressure differences like that anymore, not even close.

The inner connector easily disconnects from the interface connector. No water evident anywhere around this, which would likely be mixed up with the tranny fluid as visible blobs if it was in there. I still have my doubts about this supposed problem.

Nonetheless, it can't hurt to smear a little something into the connections as they go back together. In my perfect world grease and other contaminants *never* get into electrical connections, but I see enough other places around vehicles and electrical installations where dielectric grease is used that I'll trust it to not interfere with good sliding-pin contact in this case. Besides, what could grease do that the tranny-fluid all over everything wouldn't?

The local auto-emporium only had dielectric grease in 5-pound tubs which I certainly don't need, but since I was in there also buying lamps that day they pointed out all the little envelopes of this stuff above the lamps shelf and that I was entitled to grab at least two of them. So a modest wad of this now gets stuffed into the connector and everything reassembled.

Recall how the first-gen Prius [and now the third-gen too, ironically enough] has a genuine "muffler bearing", one of those terms used to confuse garage customers or rookie parts-counter guys? Well, this makes it clear that blinker fluid exists in real life, too.

As long as we're reminded about obscure car parts, we should also peek in and check the flux capacitor, making sure that the driveline pressure changes haven't altered its harmonic balance. No servicing needed here -- positronic vector flow is nice and stable, and the power connections look good. And we're up over 18 megazoobs today!

Hymotion, eat your heart out.

Finally the transmission fluid itself is changed, which has become such a routine procedure for many DIYers that doesn't need to be explained all over again. There are a couple of related pages in the reference section below. This, the car's second fill, doesn't look too bad with 57 K or so on it.

The only new hack added to my procedure this time is looking into the fill-hole with a mirror and flashlight and being able to actually see the level inside after pouring the first three quarts, giving a better guide as to how much more to add but avoid overflowing. Note -- if the car is up on ramps at the front and the level brought right up to the fill-hole edge, the transaxle may wind up slightly *overfilled* once the car is back down to level.


In addition to the external links embedded in the text, these are also worth reading for supporting material.

Brake fluid
FASCAR and Brake Fluid Chemistry
NIST corrosion investigation in ABS
More brake references hosted by Phoenix Systems
Car Bibles: all about brakes which touches briefly on fluids

Inverter pump
Pump takes a dive, a fairly long-running Priuschat thread
How to replace, Patrick Wong's rundown on replacing his pump
Carolyn at Luscious Garage has replaced her share of them
Pump failed today, another recent story

Acustrip 1550 type 2-way test strips
Coolant glossary from "Cool Profits" magazine
Coolants and Corrosion -- San Carlos Radiator, with pictures of "spent" coolants and corroded parts
Electrolysis explained -- San Carlos Radiator
Another coolant glossary from Suncoast
Extended life coolants esp. for trucks
Antifreeze Additive Packages by WEBA Corp
Coolant FAQ aka a couple of article copies at "unofficial BMW"
Correcting Coolant Confusion -- Underhood Service
Overall cooling system service from Larry Carley
Cool Head on Coolants from ASAshop
More on corrosion inhibitors from Google Answers

Fuel system cleaners
Bad gas and deposits, Larry Carley on gas quality and additives
Bad Gas Update: more from Larry Carley
Texaco FAQs about Techron and related topics

PCV valves
Positive Crankcase Ventilation from aa1car, good description/diagrams
PCV teardown [for Hondas, but they're all mostly the same]
PCV replacement how-to from Galaxee and her DH over at Priuschat

Transaxle fluid changes
Jesse's Classic while it was still alive
Longish Priuschat discussion on various strategies/tricks to aid transaxle fluid changes
Art's 30K Prius service includes the early ATF-WS changeout [but *way* jumps the gun on coolants]

Suspension and struts
DIY strut-replacement guide from Patrick Wong on Priuschat
Spring upgrade VFAQ on lowering the car

Flux capacitors
Back to the Future of angular aesthetics: K-cars

_H* 091009