P0A78 + P0A90 DC Drive Issues

Drive Motor A Performance.

It may just be a blown Inverter or you lost the Inverter coolant pump. Open the hood and while the car is in READY open the Inverter coolant reservoir and with a flashlight peer down into the coolant tank. Should see pretty violent agitation for circulation. No agitation the pump is blown. It takes out a fuse too if it shorts out.

 

Don't do that. There's not much to see or do under there. Just alot of connections. And exposure to hi voltage if hi voltage safety is not observed. You have to disable the hybrid battery by pulling the orange interlock. Just check the pump for good flow.

Those codes you listed are rarely are thrown by themselves. I think your not seeing all the codes on board. I would purchase a mini vci that has Techstream and harvest all the codes which will point you to the real issue. Upon reflection most likely the trans.

You can do one test that may be revealing.
On top of the 12 volt battery is 2 wires into the positive assy on top of the pos post. One thick one smaller. Those wires are removable by unclicking there white plastic clips connector by squeezing the tab and pulling them out. Disconnect both of them and then reinstall them. That will reset the car and clear all codes. See how it drives after that and how long before the codes return.

 

Mini VCI costs ~$25. It will give you the same diagnostic power that a Toyota dealer tech has. So you need to decide whether that is useful to you or not.

The inverter or the transaxle most likely has failed. The three character info codes will potentially help to determine which is the failed component. It is possible that a wiring harness problem may be the root cause, and you can use the factory repair manual info at techinfo.toyota.com to obtain the troubleshooting tree.

If you prefer to blindly replace the inverter first, then the transaxle if the inverter is not the failed part, that is up to you.

 

Yes

 

That device is generic and intended to work with many manufacturers' automobiles. The three-digit info codes are unique to Toyota so it is not reasonable to expect a generic device to retrieve those.

 

This is not exactly true - the Mini VCI is useless until it is connected to a 32 bit, Windows XP or Windows 7 laptop which when new cost much more than $100.

 

It is now time for you to purchase access to the factory repair manual so that you can perform the troubleshooting tree on P0A78, info 279 and 287.

techinfo.toyota.com

Basically, the manual suggests you check the connections to the hybrid vehicle ECU and the inverter. If the connections are good, then the troubleshooting tree helps you to decide whether the problem is the HV ECU, transaxle or inverter based upon the EXCLUSIVE INFO 4 measurement.

 

That is a measurement available via Mini VCI.

 

I don't remember anyone having connection problems in that circuit with the exception of a salvage car that saw previous trauma from an accident. Is it a salvage car? Is it new to you?

I suppose major corrosion could be an issue also. Car has lots of miles. is it really corroded bad down under?

Whatever you do make sure you pull the orange safety interlock on the Hybrid Battery. Don't open the cover on the Inverter without doing that as you could get blasted.

There's another option to the mini vci and its simpler to get going:

New Vxdiag VCX Nano for Toyota Tis Techstream Diagnostic Tool V10 10 018 | eBay

I have both. The VXDIAG is plug and play. Both require XP.

Given the miles I think you will find the trans is blown. Inverter failures are pretty rare unless the Inverter was seriously overheated somewhere in its life from an earlier pump failure. Did that happen?
If Inverter fail they usually go out completely making the car unable to go Ready.

if it was me I would pull the trans fluid and see how it looks. Any metal in it and does it smell burnt and before you dump it is it at the full line.
Full line being open the fill plug and with the car fairly level put your finger in the hole and can you feel the fluid. if so its full. No fluid its low. Its easy and pretty fast and cheap.

Go to techinfo.toyota.com and make sure your printer has good ink and paper and buy the one day subscription.
Search code tree for you codes
trans fluid change
inverter R & R
power interconnect from trans to inverter R & R
print away

There's also alot of info on the site lusciousgarage.com
They are the Premier Prius repair center.

 

Drive motor performance is measured by pulse gen & freq gen off there respective sensors. PG & FG. At speed (rev) calculated it expects a certain amount of power and not seeing it. You may have a bad fg circuit which we have seen before. There's is a plug on the front bumper side of the trans that is a known rot/corrosion issue. I believe that is the trans fg sensor output. There's a you tube about it also if memory serves. Take that plug off and inspect is closely for corrosion.