Intermittent Hybrid System Problems

[bingmel1]

I have a 2005 Toyota Prius that suddenly began displaying several error messages after the air conditioning system had been repaired and the Coolant Heat Storage Water Pump System (R & R Water Pump Assembly w/Motor & Bracket) had been replaced. The car operated with no problems prior to these repairs, and I hope that someone on this Forum can tell me what may be causing these issues.

While driving the Prius for about 15 minutes with the air conditioning running at maximum, the Multi-Information Display suddenly illuminated the Hybrid System Warning Light (red car with exclamation point in the middle). The Instrument Cluster immediately lit the Master Warning LightMalfunction Indicator Lamp (yellow engine check light). A few minutes later, the Brake System Warning Light (yellow bracketed circle with exclamation point in the center) began to glow which led the air conditioning system to suddenly not blow cold air. I did notice that the air conditioner did not consistently blow cool air prior to all these warning lights coming on (sometimes, this air would be ambient temperature or a bit warm). Obviously, I took the car back to the Toyota Dealership for further diagnosis. They cleared the errors, but the lights reappeared as mentioned above. After a few days of trial, the Dealership is still investigating.

Has anyone even come close to seeing these issues on their car? My Prius only has 26K, and has been well cared for. I'm hoping this could only be a loose connection caused by the above repairs. Anyway, thanks in advance for your feedback on this post.

[Patrick Wong]

What repairs were performed on the air conditioning system?

Lacking a list of the DTC logged by your vehicle, my guess is that the inverter coolant pump failed, which caused the inverter to overheat. After it overheated, the DC to DC converter does not maintain the proper voltage on the 12VDC bus, causing the brake system warning light to come on. Further, after the inverter overheated, the inverter circuitry powering the air conditioning compressor shut down.

[galaxee]

not really too much to go on here... if they replaced the water pump the engine coolant loop might not have been bled properly. it's tricky to do.

[bingmel1]

Thanks for the information thus far. To further elaborate on what had been repaired on the Prius, the body shop removed the radiator to further align the metal sidings as well as replace the AC Compressor. The Inverter Coolant Pump also had a slow leak, which prompted them to replace that as well. The error messages began appearing a few minutes after I drove away from the body shop.

It seems that (based on my research thus far) air pockets within the Inverter Coolant System may be causing the Inverter to overheat and issue the error codes before shutting down. I visited the Dealership first thing Monday morning to discuss my investigations and look at the car. When we viewed the Inverter Coolant Reservoir, the fluid definitely was lower than the low limit line. The electric pump also failed to start when required. We left the reservoir cap off the reservoir in preparation for the tech to fill the bottle, but when I came back about an hour later the reservoir was empty and pink coolant could be seen underneath the car.

Needless to say, there is an obvious leak in the Inverter Coolant System. I wonder if they tightened every hose connection? Interesting turn of events, and I definitely will keep everyone informed.

[galaxee]

that air bleeding procedure is tough to get right, as i mentioned above. this is true for both coolant loops. if there's a leak, then that's a big problem.

what exactly did they do to the radiator?

[bingmel1]

I gave the Dealership the repair order from the body shop to help them with their investigations, but I believe the only thing the body shop did was remove the radiator to further straighten its side supports due to a previous mishap. The air conditioning system also needed repair since it did not consistently blow cold air into the cabin (I live in Texas). Had I known I would have these problems AFTER a repair, I would have left the car the way it was since I had no trouble with the Prius up to that point. Nevertheless, the Dealership and I now have to determine what could be causing the leak of the Inverter Coolant System.

I admit I'm astonished as to why the Dealership would take so long to find a leak, since a leaky connection visually stands out like a dripping faucet. I would guess this leak may be located around the hoses connecting the radiator (which the body shop removed) and / or the Inverter Pump (which the Dealership replaced). Anyway, I'll post more information as I obtain it.

As for error codes, the only thing I can muster from the paper the Dealership gave me is Code 200 (which had been circled). I have not asked them a complete code listing since I want to keep the Dealership on my good side (it seems they won't charge me for their investigations, but we shall see).

[hc167]

I do not know what is going on but it is very possible that the dealer forgot to reconnect some of the sensors. of course I am only guessing.

[bingmel1]

Here's an update as of 23Jul2008. I've taken the car to two Toyota Dealerships and two independent shops thus far, had the Inverter Pump replaced and its coolant system filled and purged of air, but the above error lights appear again!!! It seems to be a heat-related issue since the codes show up after driving the car on surface roads for about 10 minutes (the car runs well on the freeway). In the morning, the car starts with no error lights whatsoever but eventually turn on after the engine compartment warms up with the hood closed.

I'm going to visually check around the engine compartment tomorrow to determine if there is a stray sensor or any kinked hoses. If all seems well, I'll have to take the Prius back to the dealership for further diagnosis. I'll also continue my online investigations on how the Prius Inverter operates. Can anyone tell me how the Inverter System senses an overheated condition? Where are the sensors located? What about radiator / condenser temperature sensors? What is the overtemp setpoint of the Inverter System? Any other information would certainly be appreciated.

[Patrick Wong]

The inverter has temperature sensors within the physical assembly.

In your post #6 you mentioned that the Prius suffered a previous mishap - I assume that this was accident damage?

One possible reason for overheating is if the radiator fans are inoperative. When the car is hot enough for warning lights to come on, are the fans operating? They should also be running whenever the air conditioning compressor is on.

Assuming that the fans are working: when you get the car hot enough so that the radiator fans are blowing, please note whether the fans are sucking air from the front of the car, or blowing air towards the front. If the latter, then the fan blades are incorrectly assembled.

Another poster recently pointed out that the two fan motors rotate in opposite directions; hence it is important that the correct blade assembly is mounted to the correct motor. His Prius had the blades reversed, so this caused overheating problems. A further symptom of this was that the outside temp displayed on the MFD was much higher than ambient temps, when the fans were operating. This is because hot air from the engine compartment was being blown towards the outside air temp sensor mounted in front of the radiator.

[bingmel1]

Interesting information! I also read a post where the radiator fan had been installed reversed and caused overheating. The radiator fan operates on my Prius, but I'll have to check in the morning which way the air flows.

Can you elaborate on the two fan motors of the radiator, their orientation, and the minimum air flow required through each fan? Is there a way to adjust the position of the fan assembly on the radiator housing for better air flow? I didn't realize the Prius has a two-fan radiator design, but then again I have not completely remove the front engine molding to notice a second fan (I only saw one through the molding crevices).