2nd Generation Prius Issues - Water Pump

I had some issues with my 2nd Generation Prius that I wanted to share. On a hot day (115F), my wife started driving my car around town, and I got a call that the check engine light, and the big red triangle had come on. She pulled over and didn't know what do to. I came out and checked all of the fluids, and everything was good. I noticed that I could not keep my hand on the inverter for more then a half second, pretty hot. I know I had a recall on the electric water pump, but I was not sure if that was the cause of this issue. I was able to get the car home by driving slow.

I didn't want to blindly take my car to a dealer without knowing what code the car was throwing. I picked up a ScanGuageII from the local AutoZone. When I hooked it up and checked for codes, it only had one.

P0A93

The car cooled down in the garage. I cleared the code and wanted to see if the code would come up again. I drove my car around and everything seemed fine. I found the following values, and programmed them into my ScanGuageII:

Inverter Temperature – MG1 07E221C3 032300000000 4808 00090005FFC6 IT1 F

Inverter Temperature – MG2 07E221C3 032400000000 1808 00090005FFC6 IT2 F

While driving around town that evening, I measured a temp on MG1 peaking around 170F. I was not sure if this was high or average, but based on the fact that the car seemed ok in the cooler evening hours, it must be the pump during the hot parts of the day.

The next day, it was hot again, and here is what I observed. The temperature got really high on MG1 & MG2, and eventually I saw a drop in voltage from 13+ to around 12 volts. No alarms were generated though. This appeared to be the DC-DC Charging circuit for the battery being shutdown. Strange, because the fans for the vents inside the car run off that battery. I also a noticable change in the RPM of those fans when that circuit was turned on and off. The AC Conpressor was not running, and producing cold either.

Eventually, the voltage I was monitoring fell to around 11 Volts, at which time the car threw the same error code (P0A93). It appears that when the inverter gets to hot, the Prius starts turning off some systems, to include the DC-DC Charging Circuit for the battery in the back of the car. This continued to point to the recalled Electric Water Pump that cools the inverter.

I let the car cool back down for a while, and was again able to make it back home. I scheduled a visit with the local dealer for the recall repair.

After the water pump was replaced, I have not seen a temperature on MG1 or MG2 get above 130F for more than a few seconds. This recall appears to have resolved the weird issues that occurred with my Prius. I hope this information helps somebody out.

According to Toyota:
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Approximately 350,000 of these same Prius vehicles are also being recalled to replace the electric water pump for the hybrid system.

In the hybrid system, there is an electrically driven water pump that circulates coolant through the hybrid components to provide cooling. There is a possibility that the electric motor installed in the water pump may stop functioning, leading to illumination of various warning lights in the instrument panel. In limited instances, the electric power supply circuit fuse may open, causing the hybrid system to stop while the vehicle is being driven.

Toyota dealers will replace the electric water pump for the hybrid system. The repair will take approximately two hours depending on the dealer’s work schedule.

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Ref: http://pressroom.toyota.com/safety-recall/toyota+safety+recall+2004+2009+prius+nov14.htm?siteid=DMG_rss_201211_RLA_explan_toynew_Toyota+Announces+Voluntary+Safety+Recalls+of+Certain+2004+to+2009+Model+Year+Prius+Vehicles