Servomotor from hell

Hey everybody — I’ve got three servomotor-related problems in under a year on a Prius prime and am not dumb enough to believe they are all unrelated (note: I totallu AM dumb enough to believe the first two were unrelated, but the service center is pushing its luck by going for the hat trick).

All three times the symptom’s been the same: the car abruptly starts blowing hot air only, all the time. The problem first appeared when the car was still under warranty, thus the service center.

On the first go, they inspected the servomotor circuit and then decided the problem was the auxiliary battery, which they replaced. AC then worked for six months.

On the second go, they pulled out the external condenser refrigerant temperature sensor circuit. It looked fine, so they reinstalled it — and again, it worked. It cost a couple hundred bucks.

the third time is currently happening. the diagnostic computer is apparently spitting out a different code than the other times, but it’s again servomotor related. I’ve included the two past write ups.

I’d love to conclusively get this conclusively fixed, but I would even more love to figure out if there’s a common cause. (If there is, I should be able to get the work done unded warranty due to the fact that they missed it in the first case.) otherwise this is going to cost several grand.

Any thoughts about what the culprit is here?

 

So I've had three A/C servo-motor related issues in under a year on a 2017 Prime and I would be very glad for some thoughts. In all instances, the symptom's the same: the A/C abruptly puts on hot air, full-blast. (The actual A/C unit is fine).

The first time I took the car in (still under warranty) they investigated servomotor stuff before replacing the auxiliary battery -- at which point the A/C started working again. So they called it a defective battery and replaced that (though there were no other indications of a bad battery).

The second time, they removed the external condenser refrigerant temperature sensor and tested it. It passed, and they put it back in, everything started working again. It cost me a couple hundred bucks.

The third time is going on now -- Exact same problem of abruptly turning on hot air at full blast. I've been told this is a totally different issue and also that it's going to cost quite a bit -- $1,700 just to get the dash unit out of the way.

Per the official service center, these incidents are all unrelated - and thus not covered under warranty after the first visit. I'm having a hard time believing I've had a hat trick of unrelated problems that all resulted in the exact same problem, but I am out my depth here.

Any thoughts from people who're smarter about this stuff than me? Does the initial determination of a bad aux battery make sense, given that the only thing that was failing was the servomotor? And is there some potential root cause of this stuff? It's been throwing off codes like B1441 and B1380, and I've included the notes from the service center.

 

(Also sorry for the duplicate post -- the first one didn't show up for a few hours and I couldn't find it under the "my content.")

 

I'll try. Thank you!

 

Okay. Got the codes from the service center - b1441 and B1448. (Though I'm kind of second guessing whether they read them to me right, as a B14B8 would also make more sense, unless there's some connection to the Wiper sensor going on here that I don't understand.

The best I'm coming up with googling is the below:

|What is B1441 TOYOTA code meaning?

The Air Mix Damper Servo sends pulse signals to indicate the damper position to the air conditioning amplifier. The Air Conditioning Amplifier activates the motor (normal or reverse) based on these signals to move the air mix damper (passenger seat) to the appropriate position. This adjusts the amount of air passing through the heater core after passing the evaporator and controls the temperature of the blown air.

B-14B8
This DTC is stored if the amount of refrigerant in the air conditioning system is insufficient. The air conditioning amplifier assembly receives the ambient temperature signal, refrigerant pressure signal, etc. from various sensors. Based on these signals, the air conditioning amplifier assembly detects the amount of refrigerant. The A/C switch indicator is turned off and the air conditioning system is stopped if the amount of refrigerant is insufficient.

Any sense of how this might fit into the pattery of abruptly blowing hot air?

 

I wish. It's a 2017 vehicle, and the first time the constant hot air problem began was just before the warranty expired last year. Then the problem came back twice over the next ten months.

 

Okay, now I've gone down a bit of a rabbit hole and found TSB MC-10176693-9999 that sounds a lot like what I've been dealing with and even has the same codes listed, including B1448. For those vehicles, it was a software issue. But.... the bulletin was specific to Land Cruisers. Sigh.

 

... and illustrating the point that you just made, that TSB I just looked up listed the code 1448, which is not the "generic" one pertaining to wiper sensors that I'd cited. It's the passenger side face servomotor circuit. At least in land cruisers!

So my two codes are B1448 (Passenger Side Face Servo Motor Circuit) and B1441 (the Air Mix Damper Control Servo Motor Circuit.)

I'm kind of bummed the problem isn't that my Prius is actually a Land Cruiser. Then I'd be all set.

On a more general front: I'm grateful that somebody like you's even taking the time to think this through. I've seen your other posts in my research and it seems possibly that you're the world's foremost public expert on Prius servomotor problems.

 

I am in awe of how thorough this analysis is. What a great thing to wake up to.

 

Update here (and further praise for Elektroingenieur).

I researched everything he wrote about so I could understand it well enough to discuss, then on Monday had a talk with the senior mechanic at the Toyota One dealership in Oakland. I walked the mechanic through the case that Elektroingenieur made of overlapping problems, based on both the recurrence of the code and the logic that the auxiliary battery was unlikely to affect servomotor performance in Ready state. He acknowledged the plausibility of the argument, and asked me to authorize the sub-assembly disassembly to figure out if that was in fact what was going wrong.

A day later he called to say both that the servomotor had in fact failed and that Elektroingenieur's description of the likely decision tree they went through on the first repair under warranty was spot-on. He then said he was going to need to talk to Toyota corporate. (I've found this dealership to be pretty stand-up).

Two days later, Toyota agreed to eat the full repair cost. There's no doubt in my mind that the advice I received on this thread likely saved me north of $5,000, partly because it guided the diagnostic work and partly because it was apparent he and I were both working off the same set of facts.

@Elektroingenieur, I would happily send you a consulting fee on this. I'm also happy to donate a few bucks to PriusChat's operating costs if there's a way to do that.