How to Replace the Inverter Coolant Pump

Fascinating! I took another look at the older pump (and an extra bolt and it basically bottoms out on the metal piece....leaving it fairly loose....

pretty cool design!

 

Btw...i always assumed the inverter fluid was in a sealed system. But whenever there was overflow, the excess would go out of a tube that is completely open (2008 prius). So is this a sealed system or is it completely open to the elements?

 

Some might go out that tube if it overheats enough for the pressure to exceed what's marked on that cap label. Other than that, it's sealed.

 

In my case....when i was pouring fluid in...it would go right out the overflow tube when it reached the high point. Did not seem sealed at all....

 

What are you calling the high point? The H mark on the bottle is well below the overflow tube.

 

When i was pouring in the coolant, once it reached the top of the cap (above the high mark), the excess would pour out of the drain tube...

 

Ah. Like in the Henny Youngman joke, don't do that.

 

How do you know if the inverter coolant pump is working or not? If the inverter coolant pump fails what codes does it show or what are the symptoms?

 

If the pump fails and it is a hot day the car will throw a code. Various things may go wrong first, like it turning off the A/C without being instructed to do so. This is usually how people find out that their inverter pump has failed.

If the car is in READY and the pump is working, if the cap on its reservoir (next to the inverter, NOT the radiator cap!) is off you will see motion in the fluid. Sometimes that motion can be hard to see - I vaguely recall somebody saying that if the fluid level was too low it wouldn't be visible.

If the pump is loose it can be bench tested by running a water filled tube from the top into a bucket of water, apply 12V, and it will pump. It is not self priming, in that if there is an air filled tube going to a bucket of water it will just spin and never move any water. Do not run one of these pumps dry, it will trash it in short order.

 

ok thanks, im a newb to the hybrids so i was not really sure what i was doing. I had the radiator and the inverter coolant reservoir disconnected and off the car then i turned the ignition key to the on position not start position to check the battery condition with the scan tool. I heard a humming noise and was like what is that noise. After a few minutes i figured out it was coming from the electric coolant pump and was like oh no thats not good so i turned the key off. I replaced the radiator and inverter coolant reservoir and filled with fluid. Now i just want to make sure i did not damage the electric coolant pump. When i turn the key on i hear a little hum but i do not see any coolant movement in the inverter reservoir at all. I did fill the reservoir over full and to the top so i am not sure if thats why i cant see any movement or not. I have drove the car about 60 miles now since then and i dont get any codes about the inverter coolant temp but it is 30 degrees outside temp. I would just replace the pump but they are expensive so i am just trying to make sure mine works correctly. Sounds like the best way to make sure its working is bench test it?

 

Kind of a lot of work to take it out again. There is a bleed valve for this loop (look in this forum, there is a long thread on replacing this pump which has pictures and instructions). Put a piece of clear tube on it and route the other end to the top of the reservoir. Put the car in READY. If the pump is receiving 12V and no fluid comes out either the valve isn't open or the pump is broken. If everything is working you will probably also see some bubbles going through the tube.

 

i will get clear hosing and try to bleed both of the hoses. If fluid moves i will know the pump is working and leave it alone. If no fluid moves out the bleeder valves i will replace the inverter pump. thanks much for the info

 

I don't understand what you mean by "bleed both of the hoses". The cooling loop is what is bled, not each hose individually, and it also gets the air out of the non-hose parts of the loop, for instance, the inside of the inverter.

Note that it is critical that the bleed hose end above the fluid in the reservoir. If it is placed lower than that fluid will (or at least should) come out of it just from the fluid pressure in the system, even if the pump is not moving at all.

 

on the front of the inverter box there is two 10mm nut valves that you can hook a clear hose up to and turn the nut to allow coolant to flow through the bleeder. Sorry i have a gen 1 so maybe a little different, im not sure. I think we are talking about the same bleeder though.

 

There is only one bleeder valve on the 2nd Generation. I guess if a gen 1 has two bleeder valves then probably it is because it needs to be bled from both. That said, my previous comments about placement of the end of the bleed tube still apply.

 

Gen 1 is different because of the two bleed valves, and requires extra thought because one of those two goes to a hose feeding the suction side of the pump, and if you're not careful it sucks air in and defeats your intention of bleeding air out.

If you have a Gen 1, you can look at this post.

You can follow the way Toyota says in the manual, but that involves turning the pump off every time you're going to open the valves, and closing the valves every time you're going to turn the pump on (so you never have the valves open and the pump on and air being sucked in), and if you're clean-shaven when you start you look like Methuselah by the time you're done doing it that way.

 

Does the coolant loop for Gen 1 have two high points, one for each valve? What would happen if you ran the inlet side tube to near the bottom of the reservoir and the outlet side tube to just above the fluid in the reservoir? Seems like it should eventually fill the inlet side to the top of that valve, but the short circuit might be so much that it wouldn't get the bubbles out of the loop that isn't in the section with the pump, between those two valves.

 

Good thread. The pump went out yesterday at 190k miles. First time for me, but I think a previous owner had had it replaced once already, at the dealership, at around 100k.

I believe the hybrid system has multiple stages of warnings and self-protection from overheating. I was driving on the interstate in 90 degree weather when the pump failed. Upon the first sign of a problem (red triangle, check engine and ECB ((!)) lights) the A/C stopped blowing cold. The blower would still run at all its speeds, and I think it was cooling slightly, but there was an obvious reduction of performance. I kept the A/C off after that, so I'm not sure if the A/C comes back when the inverter cools down. The throttle response seemed to change while overheating: normal driving power was available, but required more pedal (it's possible I imagined this). Pushing the car too hard resulted in more obvious problems: the DC-DC converter started to behave erratically, resulting in noticeable flickering of dashboard lights and the 12v bus voltage jumping all over the place (as measured by the MFD in its diagnostic mode. This may be what sets off the ECB light, not sure.), available power was definitely reduced, and the combination meter buzzer sounded continuously for several seconds (forgive me for not exploring this condition very much ).

I also found that the top cover of the inverter was much too hot to touch during this exercise, whereas I seem to remember that, normally, it only gets mildly to unpleasantly warm while driving (I'll have to check this, now that the pump is replaced...)

I babied the car the rest of the way to my destination, about 200 miles. After sunset, it seemed ok with going 50-55 mph. Obviously this isn't the best idea--I await a latent inverter or MG failure--but, also, maybe it's fine! If trying to get somewhere with the pump out, I'm not sure it makes sense to stop and wait for the system to cool any more than you have to. Without airflow through the engine bay it seems to stay hot for a long time.

A local shop wanted $1800 to replace the pump along with the coolant control valve, which they insisted was also important for cooling (it's not). I won't be going back there. I picked up a new pump and SLLC from the dealer.

Like some others in this thread, I opted to remove the driver-side headlight housing for easier access to the pump. This really does make the pump much easier to get to; I would definitely recommend doing it this way the first time, or if you have big hands.

As part of the pump replacement I drained and refilled the coolant rather than trying to keep it in. That seems like common sense after the system has been overheated, plus, I think I would have made a mess otherwise, and the coolant was past due to be changed. (On that note, remind me to do the engine coolant--not to mention ATF--soon. As soon as I recover from that shop's $200 diagnostic charge.)

The one detail missing from the OP is the location of the bleed screw, which took me a few minutes to find.

In order to run the pump intermittently for bleeding, I loosened the harness connector S27/S28 just behind the fuse box. This is the same connector you can use to isolate the pump (making the car driveable) when it fails short and blows AM2 repeatedly (mine did not fail short). It also gives a convenient way to turn a working pump on and off from the engine bay, so you can just leave the car in IG-ON while you do the bleeding.

These pumps clearly have a limited life. As suggested earlier in the thread, it wouldn't be a bad idea to start carrying a spare with you after 50k-70k miles or so. I'm also thinking about mods to run the pump slower, or turn it off, when the hybrid system isn't working hard. I remember reading that this pump is variable-speed in gen3.

 

It would suck fluid in through that tube, instead of bleeding air out there.

When the pump is running, there's a suction at that point of about −10 inches of water.

So if you run a tube from that bleed valve down toward a jug on the ground (more than a 10 inch drop), and make sure that tube is full of coolant when you start, then you can open that bleeder with the pump running and still get an outward flow there that removes the air. That approach is described in this post.

You do have to keep an eye on the reservoir level and keep it from getting too low, since the flow out this tube will be going to the jug on the ground instead of back to the reservoir.