Wiring Diagram Question

Hello all,

I think this is an appropriate forum to ask my question.

Can anyone out there read wiring diagrams?
I have a 2012 Scion IQ (North American) and I am trying to determine the 3 wires (live, ground, flow sensor signal) that are coming from the Flow Sensor atop the A/C compressor going to the wiring loom that plugs into the A/C ECU.

I've attached a .pdf provided to me by Toyota. I am not sure how these wiring diagrams work but it doesn't have a legend of any sort.
On Page 2 I see SOL+ (Red PIN 13), FLOQ (Sky Blue PIN 4) and SG-1 (Violet PIN 23). Which I believe are the 5v live, the flow sensor signal and the ground in that order but I am unsure.

Thanks, hope someone can help!

Thanks for attaching the diagram! Perfect forum to answer this question. This is what I'm getting out of this diagram:

SOL+: PWM power feed for the variable displacement solenoid. SOL- is permanently grounded.

FLOQ: Flow sensor signal to the Amplifier.

SG-1: Sensor ground.

S5-3: 5V reference. S5FL at the compressor.

We can be pretty sure S5-3 is the 5V ref because it's shared with the A/C pressure sensor, and the pressure sensor shows a '+' at pin 3. The SOL circuit is wired that way because Toyota (and most other makes) have been power side switching these solenoids for years.

Toyota loves their obscure circuit designations, huh? :silly: You pretty much have to have the pin voltage chart in front of you WITH the diagram to sort it out.

I'm at a loss for words... I have been trying to figure this out for weeks. My girlfriend is about ready to kick me out because this has consumed me!!!
Thank you so much Tyler. This will save me $3,241 at Toyota to "fix" my issue. I will also be sharing this information with other Scion IQ owners incase they run into this.

So the FLOQ is the flow sensor signal as I thought, the SG-1 is the ground as I thought but the S5-3 is the 5v live! Not the SOL+ wire.
All of this is way over my head but I am determined to fix my A/C problem.
My flow sensor reads 3.6v (with Toyota Techstream) and in order for it to engage the magnetic clutch I need it to be between 3.8 - 4.2v. So after searching online I found my solution - a non-inverting operational amplifier. Which I have built and ready to solder in.

Thanks a million

No problem at all! Glad to hear that info helped you out.

For our info (and anyone else that comes along later), what's your specific issue? No compressor engagement? What did the dealer find and what parts did they quote for a repair?

I'm pretty familiar with Toyota's variable displacement systems, but haven't seen a 'flow sensor' yet. :huh: Do you have any info or insight into what role this sensor plays?

Basically the A/C wasn't working which prompted me to go to a Toyota Service center for an A/C Diagnostic. They recharged the refrigerant because there was none in the system and came back with 1. There is no leaks at this time and 2. The A/C Compressor wasn't turning on.
So I started my research online and found several forums talking about Toyota, Scion and Lexus A/C problems relating to a DTC code B1479. These people were using a program called Techstream to plug into the car's OBD reader which plugs into the laptop. I found the same code in this program and was able to manually engage the magnetic clutch and sure enough cold air came out. My Flow Sensor voltage was reading 3.6v according to Techstream. The flow sensor sits atop the A/C Compressor and is told by the A/C Amplifier Assembly or A/C ECU for short, when to engage the clutch and start pumping refrigerant thru the lines to produce cold air in the vents. It needs atleast 3.8 volts to engage then the voltage will lower depending on how much refrigerant is needed to cool the vehicle. I was reading that once the compressor turned on - the lower the voltage the more refrigerant is pumped thru. I don't completely understand how it works but that was what was said.
The "fix" these people were discussing was building a non-inverting operational amplifier to boost the voltage on the flow sensor wires.

This all comes from two websites, this being the primary source of information -
www.clublexus.com/forums/rx-3rd-gen-2010...-cheap-solution.html

There was 3 options in that thread:
Replace the flow sensor (the one I need is not readily available) and would be a ton of work to get to.
Boost the voltage to the flow sensor to get it to operational parameters
OR
Replace the entire A/C Compressor (just for the flow sensor).

The dealer didn't find much they just wanted me to pay them to replace the entire compressor which, broken down, includes a compressor & magnetic clutch ($1700), various washers, bolts etc, 4 hours labour ($417), an A/C charge ($139.95),and finally a wheel alignment ($99) because in this micro car you need to drop the subframe in order to reach the A/C compressor and remove it. It was simply not feasible for me to do that.

I will be typing up a step by step for Scion IQ owners with pictures and will include it on all websites I've posted on about this problem so anyone can fix it.

Awesome! Looking forward to the write up when it's all done.

I see that the flow sensor isn't easily accessible, but how about the amplifier? I ask because it might be worthwhile to install a variable resistor in place of the flow sensor signal. That way, you can adjust the resistance to get the voltage you want (3.8 - 4.2V), and make sure the amplifier is happy.

If the compressor runs with the resistor in place, proceed with your repair. If it doesn't, then perhaps some more digging is in order. This is how I would prove out the system were it in my bay.

Also, I'm really interested to know what kind of setup you're using to run Techstream. Which adapter, laptop requirements. How much is the subscription?

The A/C Amplifier is what I am going to be soldering this "flow sensor booster" to. It is behind the cigarette lighter/12v trim in the center console. Very easy to get to on these Scion IQ's. The booster will be soldered onto the wire loom going to the amplifier. From what I understand a variable resistor and a potentiometer are the same thing and that is what I am using on the amplifier. I believe it is a 100k pot and right now it is adjusted to what I need. This was built for me by an electronics specialist because I don't know how to do that. Pictures of this build will be included in the full write up.

Techstream was very difficult for me to install. I went on eBay and bought a cheap cracked program which came with the cable. I didn't end up using the program that was included because I couldn't get it to work on Windows 10. I downloaded an older cracked version and used an old laptop with Windows XP. That seemed to be the best OS to use with this program.
In the program you can do all kinds of things, program key fobs, change light settings, adjust alarms etc etc. Very cool to have. To get an official version you need to be a licensed technician and from what I understand it is extremely expensive.

Ordered a mini VCI from Amazon. We'll see how this goes! :silly:

I did a test earlier with mini marettes to the wires you identified and the A/C WORKS!
I drove for quite awhile with it on and it was perfect.

Do you mind if I reference/give you credit in my write up? I see you are a moderator too, would it be ok to include a link to this website?

Let me know how the cable works out for you. I went through hell trying to get that on a laptop. Windows XP worked best for me.

Please, reference/link away! Very happy to hear the A/C is back to cooling.

BTW, this kind of information is awesome for membership. For the working technicians, they now have a pretty good idea of where to start troubleshooting if they ever get this code/symptoms. For the DIY-ers, they now have a workable alternative to compressor replacement.

Here is the full document. It is overkill but it is for people like me that will need this kind of direction.

workupload.com/file/SrWkgPjV
(175mb compressed)

check out mhh auto website for techstream downloads.they have all sorts