How to Replace the Inverter Coolant Pump

[Patrick Wong]

Nice work!

Another member changed the pump by leaving the old silver sheet metal bracket in place, and unbolting the old pump from the bracket. So that's a potentially easier alternative to consider for others who DIY.

[almostrice]

My 2005 shut down this past December with the red triangle. I had it towed to my wife's warehouse. It has been bitter cold for the past 3 weeks and today was my 1st chance to do the fix. Fuse AM2 kept blowing(2nd blue fuse from the top right on pic 9). I removed the battery and charged it for a week while I figured out what to do. I put the battery back in to diagnose the problem and the car started without a problem. I could move it, but I refrained from leaving the parking lot because I had smelled burnt plastic when the call first stopped on me.

Now, I had a car with that could run but I knew something like the pump must have died. I got the pump from Champions of Houston for $87 and change. I waited until today to start fixing it because it was the 1st day above 60 degrees in the past 2 weeks for us that I had time at home.

Originally Posted by Patrick Wong

Nice work!

Another member changed the pump by leaving the old silver sheet metal bracket in place, and unbolting the old pump from the bracket. So that's a potentially easier alternative to consider for others who DIY.

I agree, I would also add removing the headlight assembly would make life a whole lot easier. Going through the hood is too much trouble. You are more apt to do damage to yourself and the car.

Just removing the headlight would make this an easy job. This method will probably be my method when I need to fix the headlights too. I did the whole job in 1.5 hours. First hour was following the original instructions. I stopped when I could not get the hoses off the old pump. I would start by removing the bumper and then the headlight assembly. The 2nd picture shows how much room there is to work when you take this step. Now removing the electrical connector and 2 hoses is a snap.

3rd and 6th pic shows the damage done by the pump and the source of the burnt plastic smell. It was easier to remove the pump from the assembly than to remove the whole assembly from the car. This is shown in the 4th and 5th pictures. pictures 5,6, and 7 are a comparison of the damage and to new pump. Pictures 8,9,and 10 are the completed pics prior to putting the headlight assembly back on. This job should take less than an hour and you should only need a 10mm socket, channel lock/pliers and some extensions.


I am glad to learn on my 2005 since my wife has a 2008 and I will need to maintain it.

Here are my pics

[Patrick Wong]

Originally Posted by almostrice

... Fuse AM2 kept blowing(2nd blue fuse from the top right on pic 9)...

3rd and 6th pic shows the damage done by the pump and the source of the burnt plastic smell...I am glad to learn on my 2005 since my wife has a 2008 and I will need to maintain it.

This is great, thanks for your post and photos. I had not previously heard of an inverter coolant pump shorting out and causing AM2 to blow, so this is a very nice addition to group knowledge.

Its also nice that you can leverage your knowledge over two vehicles.

[almostrice]

Originally Posted by Patrick Wong

This is great, thanks for your post and photos. I had not previously heard of an inverter coolant pump shorting out and causing AM2 to blow, so this is a very nice addition to group knowledge.

The AM2 fuse blowing seemed to be caused by the overheating due to the failure of the Inverter pump. I prefer fuse blowing than the Inverter. The blowing of the fuse stopped after the removal, recharge and reinstallation of the 12V battery. Car ran fine after the battery was reinstalled. I just did not drive very far. Fuse did not blow after the the 12V battery service and prior to the replacement of the inverter. I just replaced the inverter today. The car sat for 3 weeks. 1 week for the battery and 2 weeks for good weather for to replace the pump. I could have driven it the past 2 weeks, but did not want to risk damage to the inverter and paying for a tow again. Total cost was $80 for the tow, $87 for the pump and $20 for coolant. I am glad I did it myself and am not too afraid of working on the Prius anymore.

I had planned to change the inverter pump, but it failed before I could get to it.

[Patrick Wong]

Thanks for your clarification. I think that your inverter coolant pump motor failed in such a way so that it drew excessive current, thus scorching the mounting bracket and blowing the AM2 fuse. After you replaced the fuse a few times, the short circuit in the motor had sufficient heating so that it became an open circuit and the fuse could stay intact.

This is unusual, as usually the pump will fail quietly without popping the fuse and the owner has no idea a problem exists until the car is driven in hot weather so that the inverter overheats and causes 12V bus voltage to sag, which causes the various brake and VSC warning lights to come on.

Thanks also for providing the link in your post #46 below, where a similar problem apparently occurred. Good detective work on your part, glad the car is back to normal now.

[almostrice]

Originally Posted by Patrick Wong

OK, so you had to replace the inverter as well as the inverter pump? What symptoms were related to the inverter failure?

Normally the inverter would be covered by the 8 year/100K mile hybrid system warranty - is your car past that point, or is it a salvage vehicle?

Are you saying that AM2 blew due to the inverter overheating, and not due to the pump failure? Your post is the first that I've seen where the pump bottom scorched the aluminum mounting bracket.

Inverter did not fail.

214K miles. Way out of warranty

AM2 fuse do not blow due to Inverter failure. It blew because of overheating after the failure.




AM2 fuse blew after Inverter pump failure. I replaced the fuse and the fuse blew evertime after the 1st day. 3 days later, after the tow, I removed the 12v battery and recharged it. 7 days later I put the battery back and replaced the AM2 fuse. The 2005 started and moved like nothing had happened. The bad inverter pump is still in the car for 2 more weeks.

I knew something was still wrong so I looked into the inverter pump replacement where I found this tread.
priuschat.com/forums/gen-ii-prius-care-maintenance-troubleshooting/47846-no-start-after-smoke-burning-smell-front.html
(I can not add links until 5 posts)
I tried testing the pump and saw no flow in the coolant and the proximity I could smell the plastic smell that occurred that night.
This is when I decided the inverter pump is the root cause of the problems my 2005 was having.

[famtruss]

This sounds like a carbon copy of the problems we were having with our 2004 in the 700 miles from home, help! thread and the dealer didn't mention anything about the coolant pump. Should I have them take another look at it, or should I poke around in there to see if I can see anything?

[Patrick Wong]

Originally Posted by famtruss

... Should I have them take another look at it, or should I poke around in there to see if I can see anything?

By now I would have thought you'd have given up on that dealer. Suggest you look at the pump yourself. Here's how to do that:

Make the car IG-ON (not READY. You want all the dashboard warning lights to be on. Need to press the POWER button twice from IG-OFF, without depressing the brake pedal.)

Open the hood and find the inverter coolant pump behind the driver's side headlamp. This string provides lots of photos of that area. Listen to the pump. It should sound like an aquarium pump and you should not hear air bubbles.

Look at the inverter coolant reservoir. You should see turbulence in the fluid. Open the reservoir cap if necessary to look inside.

If you hear the pump running, don't hear air bubbles, and see turbulence, then the pump is good and there's no air in the system that would impede coolant flow.

If the pump is nice & shiny, then the dealer probably replaced it. If the pump is covered in dirt, consider replacing it soon for your parents, as a preventive maintenance measure. Good luck.

[almostrice]

I tried to see if there was any codes, but my reader showed nothing and it is just a general OBD2 reader. I suspected the pump because on IG-on but not Ready there was not sound from the pump. When I changed pumps, I tested immediately and felt water move under the hoses. That was when I knew I had gotten it. I used this thread and the one above to solve my problems. If there is no sound and no water flow on the hose when you turn the car into IG-on like Patrick said, then it has probably stopped working.

If a dealer had looked at it, they would probably had sent me on my way after the battery was removed and reinstalled. This is a simple procedure and cost is not too bad. These pumps probably can only go 100k at the most and should be a put on preventative maintenance list.

It is a lot easier than doing a timing belt. It is just a tad harder than changing radiator hoses. If you can turn a 10mm socket, you can probably do it yourself.