2002 (Gen 1) Prius with no heat

The cab heating system runs off the engine coolant system not the inverter pump. Find the hoses that go through the firewall to the cab, with the car completely warmed up, both hoses should be warm, if not, the heater core may be clogged up--have you been using tap water instead of coolant? Or green coolant instead of red (green has silicates, red doesn't, they don't mix well.) You likely need to have the system flushed, and the coolant replaced with distilled water and silicate free (dexxcool or Toyota) coolant. You may need a new heater core.

Good luck. BTW, the first year Pri's were imported was 2001.

 

Siphonaptera, your avatar says you have a 1999 Prius... in Illinois...
so if correct, you have a Japan-only model here in the USA, and a VERY early build.
Please check your vehicle type. NHW11 is the designation for the Gen I Prius.

A failed thermostat (failed closed) would not allow warm engine coolant into the cabin heater.
It is also possible that the water pump has failed, not moving heated water through the heat exchanger to the cabin.

Yah, an aftermarket stereo is a tricky process in the Prius, as the radio ties into the display, and is NOT straightforward to correctly bypass...

I hear it sometimes gets cold in Illinois, too...

 

I would not usually suspect the engine thermostat—its function is usually not to block flow to the heater core, but only to the radiator at the front of the car, until warmed up, so you get heat in the cabin faster.

Tessa's built-in HVAC diagnostics work by blinking a code out on the A/C light. You mentioned the light has "gone out". Does that mean you can't get it to light under any circumstances, like by turning the A/C on when the car's running?

Have you tried to request the codes? If I remember right (haven't had my Gen 1 for a while now), it was something like, key ON with mode turned off, press A/C three times, then turn mode to AUTO. I think all the HVAC control button lights flash together four times slowly, then the A/C light blinks out any diagnostics. At the very least, you'd see whether all those lights are out, or just the one in the A/C button.

Those 'lights' in the buttons are LEDs; they have crazy long lifetimes, so it is not likely they just burned out. If they are not lighting, and especially if none of them blink for check mode, your problem might actually be right in the electrical connections to the controls. You'd probably do well to re-check your steps reassembling the dash after your radio attempt; pay special attention to the white ribbon cable going to the HVAC board.

-Chap

 

You don't seem to have said what they were.

-Chap

 

That's what I like to hear! (I mean, not that you don't want to come to PriusChat again, but that you do want to know where to find the info yourself. ) You'll find all that in the Repair Manual for your model and year at techinfo.toyota.com.

Those are two-digit codes, it turns out. As they don't seem to be in order above, I'm wondering if you might have wrapped one around, so the actual sequence was 21, 23, 41, and 43.

Of those, 21 is usually a red herring. It means a low reading from the solar sensor, so you will always have that code if you weren't in bright light when you pulled codes.

23 refers to the refrigerant pressure switch; either it is actually sensing a pressure too low or too high, or the switch or wiring to it is faulty. Edit: by the way, at the likely temperatures in Illinois today, I wouldn't be surprised if the refrigerant pressure is too low to close the switch, purely because of Boyle's law. I wouldn't worry about that unless you still have the code in warmer weather and want A/C.

41 refers to the air mix damper servomotor. The air mix damper is what controls the temperature of the air blowing out by moving to change how much of the air goes through the heater core and how much goes around it. Code 41 says the position sensing signal does not change for some reason, even when the ECU commands the servo to move.

43 is the same thing but referring to the air outlet damper servomotor. That's the one that selects which outlets the air goes to (feet, face, or defrost).

I'm getting these from a 2001 manual (the dead-tree version), on pages DI-884 through DI-901. When you check at techinfo for your own model year, the pagination might not be exactly the same, but the details probably haven't changed much.

Both of those servomotors are very easily accessible on the driver side of the heater; you can just stick your head down there and look at them. The one that's hard to get to is the air inlet damper servo, but lucky you, the codes aren't showing any problem with that.

I attached a small video to this thread where you can kind of see those two servos in their native habitat. I was focusing on the air mix servo, but you can kind of see the outlet servo and linkage in there too.

-Chap

 

I love the info. I pick up here, this time about the difficulty of installing after market stereo. My CD player in my 2007 does not work correctly, and I was considering having one installed, but apparently need to be careful about this.

 

Hmm, I'd start with the techinfo subscription ... for the number of steps in their online signup, you'd think it was set up for a $15000 purchase, not $15. Then make sure you've figured out how to find the A/C section in your repair manual. Notice that, where it describes how to pull the codes you just pulled, it also describes a test mode where you can turn the temp dial to five different positions and put all the servos and other outputs through a preprogrammed series of paces, and make sure they do what they're supposed to.

Then I would just dig into why you have those servomotor codes. As I mentioned in the other thread linked above, don't worry that the manual says to remove the dash for access to those two motors. They're easily accessed if you just slither down in front of the driver's seat.

Might find an issue with the servos, or with the wiring to the servos (possibly where you might have disturbed some wiring with your stereo installation). The servos themselves are easily disassembled and cleaned if you find a problem there; I think it's unlikely (though possible) you'd need to actually replace anything.

I'd say most likely you're looking at a $0 repair, outside of your own time and effort to chase it down. When you think you're done, you can again use the test mode described above and make sure you really have all the parts doing what they should.

-Chap

 

Old thread...but I too had the same issue, the heater blowing cold air. I read a note about checking radiator fluid and bingo!. I bought the correct pink 50/50 for the Prius and filled it and the reservoir. Now I have warm/hot air but while checking things noticed no activity in the inverter water pump reservoir...not ever with the key in on only. So with all the problems with that pump in the gen 1, looks like I will need to order a pump (typically $200 online at various places). I need to post also a thread as to what (a this date) seems to be the best low budget obdII to buy that I can actually clear codes (I know it takes more expensive ones to clear abs codes)

 

Low coolant was my first guess from the headline, and if that's the case for anyone, I would suggest trying to figure out why it's low. That said, LOL, mine did this and I added coolant a few times. Never saw it leak out anywhere, but I read here, there, somewhere, that it can somehow, some way, leak, IIRC, into the intake manifold, and the solution was to take the two small rubber hoses off the throttle body and use a plastic connector to splice them together, bypassing the throttle body. I think it's for pre-heating the fuel in cold temps, so it's probably not a good idea for the OP in Illinois. But I did it here in Texas and the problem seems to have gone away. Don't add coolant anymore.