Blower Fan suddenly stopped working - Gen 1 2001 Prius

Hi there,

When faced with an interesting enough problem, sometimes the best course of action really is to register on techinfo.toyota.com, look at the service manuals (there's a paywall, but $15 for two days of access, or over the weekend, is peanuts compared to the kind of aggravation you're recounting here). The service manuals are not some sort of evil temptation that you must prove yourself by doing without. They will actually help you. (Already, they could have helped you know that the thing you're calling a resistor pack is really a pulse-width-modulated electronic motor control, and the idea that it is bypassed on high is something you're remembering from your grandfather's car, and you could have saved some face when talking with the first mechanic shop.)

In all likelihood there was only one original problem and most of the parts you've thrown at it haven't been needed ... if it were my car, I'd just slow down, refer to the manual and wiring diagram, do the indicated tests, find the problem, and then fix it.

Considering that the enter-diagnostics-mode sequence involves the fan control knob, and you don't seem able to enter diagnostics mode, it might not be unreasonable to check that control. I would first review the manual to be absolutely sure you're doing the right sequence in the right order.

Checking the fan control knob will involve removing the center finish panel; if you search here you'll find links to a video I made, aimed at improving your chances of removing it without damage.

-Chap

 

Hi Wade,

Well, so you know that if everything is operating properly, the A/C controller will always respond to your IG.ON-AC-AC-AC-FAN.AUTO sequence with four slow blinks, then go into simultaneous DTC readout and actuator test mode. Whether it reads out any DTCs depends on whether there are any; if there aren't, it goes into steady rapid blink instead. But the initial four slow blinks will always happen when you do that ... unless something quite fundamental is wrong. Something prior to the whole idea of whether you have any DTCs, something that is preventing the A/C controller from even doing what it has to do to show you the DTCs if you had any.

So you think: what is responsible for making those patterned light blinks?

• The software in the A/C controller

What inputs are needed to command the software to do that?

• The IG power source circuit (A7 pin 1 at the A/C controller, has a diagnostic section in volume 1)
• The A/C switch pushbutton (SW A/C and PSG on page 191 of the wiring diagram)
• The blower control input (BSET, PSG, PIG5 also on page 191)

because those are the three inputs you use to command the software into test mode. Either it is not happening because it's not getting part of your command (because one or more of those inputs is flaky), or it's not happening because the A/C controller itself has rung down the curtain and joined the choir invisible, and is no longer running its software).

If the controller is toast, to fix the problem you replace the controller, clear enough. It probably makes sense to test the three inputs first. The IG terminal is easy, you stick a meter on A7 pin 1 and see if it's going to 12 volts when ignition is on.

The SW A/C and BSET inputs are a little harder to get to. The buttons and rotaries aren't connected directly to the A/C controller board, they are on the "circuit, center cluster module" (55935-47020) which in turn is connected to the A/C board by a narrowish ribbon cable. The ends of that cable aren't finished in conventional connectors, they're just unfinished and slip into zero-insertion-force connectors on the two boards (or are soldered to one of the boards and ZIFed to the other one, if I remember right). Any time you take apart the center panel (say to change the illumination bulbs) you can't miss that ribbon cable, it's in the way and you have to find the ZIF connector and undo it.

The schematic on page 191 of the wiring manual is about the most you have to go on for that, but it's pretty simple; the four buttons just pull their respective circuits down to ground (PSG) when pressed, and the three rotaries are nothing but adjustable voltage dividers between PIG5 which is some constant voltage (probably 5) when ignition is on, and ground (PSG again). So you should be able to measure the voltage at BSET sweeping smoothly between 0 volts and whatever voltage PIG5 is, as you smoothly turn the knob from one end of travel to the other.

If meters are black magic to you, then you might just end up swapping the A/C controller board, or the "circuit, center cluster module" board, in whichever order, looking for something to improve.

-Chap