Inverter Coolant Pump

Master warning light (others too)?

A/C starts blowing warm?

Car shuts down after one or both of the above?

None of the above, but the car abruptly dies and shows little or no sign of life (mostly only headlights and dome lights) and won’t start (more on this towards the end)?

It’s probably your Inverter Coolant Pump, DTC P0A93.

One of the most common failures with the generation 2 Prius is the Inverter coolant pump. Unfortunately, the design is one of the few weak points. The pump runs full time all the time even if it’s not needed, and they just wear out. A Gen 2 will typically go through 2-3 pumps in their lifetime, and that’s AFTER the redesign and recall in 2007.

You can check for proper pump operation via the following video (read the video description for details):

If you don’t see the same vigorous flow as shown in the video, your pump has likely failed.

The car has no direct means of telling when the pump has failed. It only detects that the inverter is getting hotter than it should. It illuminates the warning lights and throws the code. Eventually, the safety systems disable various electrical systems as the Inverter heats up. First to go is typically the A/C (it’s all-electric and runs through the inverter) followed by the inverter shutting down altogether (car shuts off).

If the car sits overnight and cools off, things may be fine the next day… until the inverter heats up more than it should.

We don’t replace them anymore, but we recommend a shop in Tempe that does it for a VERY reasonable price, and they can generally get to you pretty quickly (they charge hundreds less than the dealer, and they only use genuine Toyota parts. Many shops will use Chinese knock-offs that cost half as much, and they pocket the difference).

Okay, so now we’re going to talk about the car being completely dead. If this doesn’t apply to you, then you can stop reading. Shorts seem to happen about 1 in 10 times. This occurs when the pump actually shorts out and blows the AM2 fuse that controls many critical systems. The AM2 fuse is 2nd down from the top right - blue 15A fuse. It is usually visibly bad, but it’s sometimes hard to tell. Check continuity to confirm.

You can also usually confirm this has occurred by placing your nose in the opening between the fuse box and the back of of the driver’s side headlamp. Sniff, and you will typically smell a “burnt electronics” smell. Here’s an image to assist:


AM2 fuse circled in green, and area circled in Red is where you would smell burnt electronics.

In this case, you have three options:

  1. Replace the fuse with a spare and hope the pump has gone open circuit. If the fuse blows again, you must unplug the pump to keep it from blowing the fuse every time.

  2. Unplug the inverter coolant pump - VERY hard to do unless you’ve done it before, but it can be done by hand. Replace the fuse, and you should be good to drive short distances.

  3. Tow it. They won’t be able to get it into neutral.

Driving without a functioning inverter coolant pump is NOT recommended except to drive to the shop. Do not use A/C or ANY other electrical devices. Best if it can be driven to the shop first thing in the morning after cooling overnight.

Good luck!

Leaking Batteries, P0AA6 and P3009

HV Leaks are the worst - first mentioned them here in the FAQ.  They are one of the few failures that can disable the car.  Fortunately, if you have a capable code reader to reset codes, or can disconnect the 12V, you can at least avoid a tow. You will be allowed to finish the drive during which the leak is detected, but the car will be disabled when you power it off.

We have recently experienced a dramatic rise in the number of leaking batteries, while it is still heavily favoring the 2008+ models, there has been a marked increase in 2006 and especially 2007 models.

As a result, we will be applying our 2008+ policy on leaking batteries to all years.

This business only works because we are able to recycle customer failed core batteries, recondition them and supply them to future customers.  We have made a decision to NOT put leaking packs back into circulation. As a result, if you have a leak code traceable to the battery, your pack will be disposed of, and you will be charged a $600 core fee. We will still collect your battery in order to take it out of circulation.

Simply put, if a customer core battery is not usable for future customers, we take a complete loss on the installation of a reconditioned pack.  This happens from time to time and is the nature of the business. While that can't be predicted, a leak can - it's a death sentence for a pack. We don't have a magical source for packs. If you've looked around, packs from salvage yards cost about $1000.  That's about what we pay for the packs we use as sources for modules we replace in the reconditioning process.

Should you choose to purchase a NEW battery, there will be no core charge as it's going straight to Toyota as a core.

We apologize for this inconvenience.

Crooked dealers

I recently received a call from a gentlemen from Yuma. Upon arriving in Phoenix, his car completely shut down.  It was towed to a local dealership in Mesa.

He was informed that he needed a new 12V and new Hybrid battery for $3500.  He made an appointment for a reconditioned battery. I personally saw the dealer output sheet and estimate.

Due to circumstances, he needed to get a rental, tow the car to our place and head back to Yuma.

We were able to take a quick look at it when it was dropped off.  To make a long story short...

He needed gas and a 12V jump start.

The dealer wanted $3500 to replace his battery.

The gentleman was from Spain with a heavy accent.  I can't help but think the dealership saw a "sucker".

He was able to return his rental car and drive home to Yuma the same day.

After gas and the 12V jump, I ran the battery through a series of charge and discharge tests. It did not show any signs of pending failure.

The root case was the failure of the combination meter - the device that displays speed, fuel level and controls ALL dash lights.  His had failed, he couldn't see how much gas he had, and he ran out of gas.  The car continued to drive on the hybrid battery until it and the 12V were depleted.

Please check our Services page for Combination Meter replacement options

Beat the Heat!

Holy Moly! It's hot out there!

Anything you can do to keep the interior temperature down in your car, the happier you and your batteries will be (HV and 12V).  The obvious include:

  1. Park in a garage.
  2. Park under shade
  3. Use a Sun Shade on your front windshield AND park facing West, so it will block the hottest sun of the day.
  4. Crack at least two of your windows 1/4"
  5. If you have the sliding cargo cover, USE IT!  Protect your cargo from prying eyes AND create a dead airspace that helps insulate the battery from the heat of the sun.

The less obvious are:

  1. Don't spare it one bit.  You're not putting a strain on the battery, you're saving it!
  2. When starting out with a hot interior, roll all 4 windows down 4" for the first 30 seconds or so - this will flush the hottest air from the interior. When it's 110°F outside, it's going to be 130-140°F inside.
  3. Treat it like you do the thermostat in your home - you don't run around adjusting all the registers indoors to blow in different directions - you just change the thermostat. The Prius is really no different.  Aim all 4 vents up and over the shoulders of the front seat occupants.  You'll get a nice breeze on both sides of their heads, and you'll circulate air nicely in the car to get the whole interior cooled - so your battery can be cooled with the cool interior air.
  4. The car will manage the climate way better than you can.  Leave it on AUTO, recirculate, and as mentioned before, just change the thermostat up and down as needed.  I leave mine on 75°F, and almost never touch it  With a little patience, you will find that you barely have to touch the A/C, and you will be as cool and comfortable as the circumstances allow.
  • Drive a little more conservatively.  Prius drivers aren't generally heavy-footed, but some of my test drives have revealed there are NASCAR wannabees in our midst.  Gentle acceleration (don't be the jackrabbit at the light, but pull away fast enough to not be a road block) along with more engine braking and less foot brake helps keep the demand low on the battery and to minimize heat.

Heat is the enemy.  It's what leads to premature failure.

AZ HOV Plates

For those that don't already know it , if you have a Hybrid HOV plate, it dies when your car dies/sells/changes owners. No exceptions.

Previously, one could transfer their plate to another vehicle. That is no longer the case.  You MUST transfer it by purchasing a qualifying vehicle, basically a plug-in hybrid.  Pure EV qualifies for alternative fuel plate and can get unlimited HOV lane access.

There is a lot of motivation to keep an HOV tagged Prius running, and there are lots of maintenance options outside the dealership!  If I were lucky enough to have one (late to the game in that regard), I'd swap engines to keep it! :)

AZ MVD page concerning Energy Efficient Plate Program:

Resetting your 12V battery

There is basically one battery code that can prevent you from starting the car.  It's a P0AA6, and I see it quite a bit more than I like.  I'm confident it has to do with the extreme heat in AZ.  I collaborate with others doing similar work in other regions, and P0AA6 codes occur 5-10X as much here in Phoenix.

A P0AA6 is a high voltage leak.  Basically, somewhere in the car, the computers are sensing a high voltage path to the body ground where it shouldn't be.  This can occur in the HV Battery (most common), in the A/C compressor (next most common), the transaxle (you pray it's not this one), the inverter (again, a little prayer is in order, but at least a salvage replacement won't completely break the bank) or the harness (shoot me please).

Once P0AA6 occurs, you are allowed to drive once more until you turn the car off.  Then you are dead in the water. This disabling is a safety feature.

In an emergency, you can disconnect your 12V battery, reconnect and wipe the code.  You will then be able to drive one more time.

The following video shows you how to access the 12V, remove the maroon cover at 1:04 and disconnect the first plug only at 1:09:

We are not affiliated with this youtuber.

Leave it disconnected for two minutes. This removes power from the dozen+ computers in the car and will clear most codes. Reconnect, and you should be able to make one more drive.

NOTE: After a 12V disconnect, the power button must be pressed two times to get it to show read. Depress the brake pedal, hit the power button, wait 2-3 seconds and hit it again. It should go into ready mode.  This is discussed in your owner's manual.  For the 2004, it's on page 231 in the NOTICE block.

You can access your owner's manual online here:

Once the car is in ready mode, it should drive normally until the HV leak is detected again. Proceed to your final destination driving conservatively.  If you go to an auto parts store to get your codes checked, make sure you leave the car in ready mode!  Don't turn it off!

If the P0AA6 is traceable to the HV battery, we can certainly help!


I really try to take the high road... BUT...

I really prefer the high road, but as I interact with customers or potential customers, I find what's going on out there appalling. I can identify two major "hybrid shops" in the Phoenix area. I haven't heard anything good about either.

One has two strikes against it... A customer had his THIRD failure of a Dorman battery under warranty... the only thing the shop would do is quote a new battery. On another occasion, the shop just punted and without troubleshooting, they suggested a replacement for nearly $5K (Not a Prius). I assessed that battery, and while it was significantly deteriorated, there were MUCH better options available for far less. Furthermore, the codes had nothing to do with the battery but a safety related system.

The other shop has only one strike against it. However, it's very concerning. The customer informed me he had taken it to the shop earlier this year for reconditioning. Right there on the case, it's marked: "7130mAh 2/1/16." I evaluated this pack, and it's capacity is less than 3,000mAh. One of two possibilities exists: 1) The shop is lying, or 2) the shop is using testing procedures and categorizations that are woefully inadequate for the task at hand. This isn't a situation where one or two cells were weak. This entire pack has deteriorated nearly uniformly across all cells. I question if ANY work was even done.

This is all I do. I don't try to be a one-stop shop. I have a specialized skill, and I'm passionate about it. There is plenty about the Prius that I don't know, but when it comes to the hybrid system and the battery in particular, I'm confident I'm among the best informed. I hope this doesn't sound like bragging/boasting. I have put in the darn time. Close to 1000 hours over the last two years, testing, tweaking and refining my process while collaborating with other organizations to further optimize it.

When you call, you're going to talk to me. When it's time to install, you'll see me. When there's a problem, yep, me again. If warranty service is required, it's going to be me replacing your battery completely free of charge, apologizing and struggling to wait to get back to the shop to find out what could possibly have happened, so I can make sure it never happens again.

I treat you as I want to be treated, and I take this VERY personally. I have 3 children. I also have a lot of adopted "kids" running around in my customer's cars. They don't mean as much to me as my actual children (I'm not totally nuts), but they are definitely a source of pride.

Thanks for reading,