2004 Loses Power In Heat

I have a 2004 Prius, ~150k miles. At about 80k I replaced the inverter coolant pump as a preventative measure, per advice here on PriusChat.

Recently, the car has shown intermittent lack of power, and abnormally sluggish acceleration, which seems similar to what I've heard about the failsafe mode of an overheating inverter, except no warning lights appear. We have had some hot days this summer in SLC, Utah (100+ deg). It's a sporatic issue that seems much worse on hot days. The weather has been hot, but we've had hot days in past years and not had this problem.

Yesterday, the car showed the worst ever such behavior, and was nearly crippled for my wife (why do these things always happen when the wife is driving alone?). She was returning home from a ~ 1hr appointment, where the car was parked in the sun, ambient air temp was ~103 deg. Car was very sluggish and ICE was revving much higher than normal. The battery fan that vents next to the rear passenger-side door was running at higher speed than she's ever heard it before. I asked her at the time about the battery level, and the display showed two bars, even though she was going mostly downhill. A/C seemed to be working, but she turned it off. She was able to limp home. It did seem that when the battery charged a bit, performance improved somewhat.

After I got home a few hours later that evening, (temp ~90-95 deg), I took it for a spin and it seemed fine. I'm pretty sure I detected a slight hiccup in power one of the times I punched it, but nothing drastic. She drove it this morning (84 deg ambient, ~75 deg overnight low) and it seemed normal, except that she could hear the battery fan (we almost never hear it running), but it was much slower than yesterday.

If it engages a failsafe mode for a hot inverter, shouldn't warning lights come on? I haven't tried to have codes checked, but there is no check engine light, so I assume that no codes are logged.

I have a dealer appt 1st thing tomorrow, but I'm afraid with no codes logged, nothing will be found. I was planning to take the car on a ~200 mile trip tomorrow evening too. While at the dealer, I will have them replace the inverter coolant pump under the recall (a nice way to get another free pump and coolant change). Maybe the pump I put in is having problems?

Revving engine and low power makes me think that the electric side of the hybrid system is being overtaxed, presumably by heat. I don't know if it's related, but in the past year or so, I've occasionally noticed that the hybrid battery shows low charge (1 or two bars) after the car has been sitting overnight, without any strenuous driving the day before. I haven't been able to nail down conditions of that.

Thanks so much in advance for any advice/feedback.

 

Thanks very much for the advice. Major bummer if it's the hybrid battery. The battery fan in the back seat is indeed running much more than usual. Haven't noticed fast swings of battery level, but will look for that.

I've read somewhere someone suggesting looking at a wrecking yard for a hybrid battery, is that advisable? Is there enough access to the cells for me to check one with a DVM, and if so, what do I check for?

I'll check the inverter pump ASAP. I forgot about being able to check it by turbulence in the reservoir.

When it's at the dealer tomorrow, I'll make sure to get a report about the battery status. And they'll be replacing the inverter pump anyway, so that will solve that problem if it exists.

I replaced the 12V a couple years ago (after the transmission wouldn't shift out of park--took a while to make that connection), but I'll check it too. Interesting that a bad 12V battery would drain the hybrid battery. I would never have guessed that to be related. How does that happen?

 

By the way, what has been a typical life for the Gen2 hybrid battery?

 

I wondered about it needing a cleaning and lack of ventilation near the battery being the problem. Thanks for the tip, I'll check it tonight. We haven't had pets in the car or drive too much on dirt, but you never know.

The reason to replace a coolant pump that is (presumably) working is that it is covered under the recall, and it gets me a new pump and coolant change on toyota's dime.

 

Took it to the dealer and nothing untoward was found. They basically said that without codes they can't diagnose anything. I told them several times I wanted a health report on the hybrid battery but the service guy said he talked to two different techs and both said there wasn't a way to check it. Said the car did that itself and if it found any problems it would log a code. Is there a specific test you know of that I can request to check hybrid battery health?

They verified good health of 12V battery and replaced the inverter coolant pump under recall. I verified turbulence in the reservoir before that work was done, so that doesn't seem to have been the problem.

They did report that the MAF sensor looked kinda dirty, so I will clean it ASAP.

My wife has noticed some hesitation again, but it hasn't had major problems since that one incident. I have noticed very slight hiccups, but usually drive it only in the evening. We haven't had any more 100+ deg days.

I basically want to catch anything that is going bad before the car strands us, if possible. So is there a known test for the hybrid battery that I can request? There are other dealers in my area I could try.

Thanks again for the advice.

 

A voltmeter test of the (unloaded) 12V battery by me showed it was ok (12.37V as I recall), I will look into that more, test loaded, etc, but it seems ok. Any tests for the hybrid battery?