07 Prius Air Conditioner Randomly Quits.

I hope that was warranty, it's a pricey part otherwise

Did they cover the basics? Eg, system charge?

 

Could be a loose connector. We've had debates in other threads about loose connectors and garbled CAN/LIN/BEAN messaging.

If still under warranty, I'd suggest a stop by the dealership. I know it's difficult to get these things to act up WHEN you want them too

 

I concur, for what it's worth. Loose CAN bus connections between devices, loose terminators, bus failures inside of devices, can all contribute to CAN comm problems.

We use the CAN bus protocol on some equipment made by my company. We have diagnostics tests for these to be certain that the linked modules are healthy, and the comms are working properly. I would assume that auto manufacturers would have CAN diagnostics tools available to their service departments?

 

Frank

You mean like a MSO or VSA? No, I wouldn't assume that at all. Not knocking service techs at dealerships, but it takes a wee bit of skill and understanding to properly use and interpret a MSO/VSA.

Eg, here are some glitches I uncovered on a CANBus problem. I used an Agilent MSO with deep memory, and auto-trigger on glitch



I've outlined the glitch



The effect of randomized noise



Here the MSO triggered on a PW glitch



I would think at a service level, it would be better to just carefully unseat and reseat all the connectors. We've had this discussion of weird combination meter "failures" that may, in fact, be caused by minute amounts of connector corrosion

jay

 

Hello Jay:

I don't really know what an auto manufacturer would train their service techs on for more in-depth troubleshooting. I've never used an MSO or VSA. The most I get to play with is a humble Tektronix THS730a. I was thinking more along the line of a PC based digitizer and some specifically written proprietary diagnostics software, that would exercise modules and look for responses.

I use digital scopes for pulse circuit troubleshooting, but not on CAN problems. Our CAN diagnostics are pretty simplistic, simply looking for pings and module ID responses from the devices on the bus. I've used the "CANscope" software for this before; but we also had a programmer in the past that wrote some code for us in NI LabVIEW. That's pretty much all we've come to rely on. Not really good enough too look at noise on the bus, but rather "is is talking or not"?

One issue that I check for is for the terminator at the end of the bus that we use. That has caused weird (intermittent) problems in the past if it wasn't attached securely. Other than a connection, when we lose the CAN communication in one of our modules, it's usually because of a power arc that takes down more than just the CANBus

Nice traces! Thanks for the pictures.

 

Frank

I completely agree it would be great to have a purpose-built tester. I realize that CANBus is fairly new for automotive fleets, but as that fleet ages, we can expect to uncover a lot of issues

Eg the combi meter "problem" in earlier 2004-2006 Prius cars. It's widely reported that replacing the +$1,500 combi meter reliably "fixes" the problem. I'm wondering if just the act of unseating and then reseating all four bus connectors also fixes the problem, and replacing the combi meter is completely unnecessary

I completely agree that terminator issues can play a big - important - part in diagnostics. Anything that can introduce randomized glitches deserves more attention, and I'm afraid the "replace parts until it works again" approach is the WRONG approach here

The Agilent I used was the slightly older brother to the InfiniiVision 6054A. It will automatically trigger on glitch, or any other parameter you chose. Overall a very smart MSO, as it should be for +$15,000.

You can also have the MSO capture the entire screen and save it internally, or on the network, as a JPEG. I find this a very useful feature when discussing errors and glitches with clients.

jay

 

I think I have little sympathy for anyone who uses a radar detector :_>

But seriously, we have read here of cases in which aftermarket electronics caused weird and/or flaky problems. Sometimes the root cause was sloppy installation.

 

In what exact way does the air conditioner not work? Do you mean that you don't get cold air when the fan is running, or that the fan doesn't run at all?

If the screen has a lot of fingerprints on, that could be confusing it. Clean it gently with a clean microfibre cloth. However, you should still be able to control the A/C using the A/C AUTO switch and the temperature controls on the steering wheel, at least if the MFD is displaying something other than the climate controls.

The diagnosis procedure for 'A/C doesn't work' in the Service Manual starts with checking that the Air Conditioning Amplifier (A/C ECU) is actually getting power at the right time. It's hanging straight off the IG1 Relay, which is basically the master ignition relay - the car wouldn't move if this relay didn't work. There is a 10A fuse marked A/C (HTR) which protects this ECU.

If the blower doesn't operate, or operates erratically or doesn't produce enough air, the next suspect is the blower motor circuit. The A/C amplifier sends pulse-width modulated signals to the blower motor controller, which converts that into a voltage to apply across the blower motor itself. The blower motor controller runs from the 40A HTR fuse, via the HTR Relay, whose coil runs from the 10A GAUGE fuse. If that appears to be OK, again the next step is to replace the A/C Amplifier.

If the blower works but you don't get cold air, even when the temperature is set to MAX COLD, then you get into checking the refrigerant volume, pressure and pressure switch, air mix damper servo and its position sensor, the room temperature and humidity sensors and the ambient temperature sensor. Replacing the MFD doesn't appear anywhere in the problem troubleshooting chart.

 

Does the fan work in heating mode? It's easy to tell if the A/C compressor is running.

With the car powered off, open the hood. Have an assistant power up the Prius. You will hear a very distinctive whine that will raise in pitch as the variable speed electric motor ramps up the compressor

 

Then they should check the blower motor circuit and find out whether it's shorted, has poor ground, or the controller just doesn't work.

The Inspection Procedure for this circuit says to plug in the diagnostic tester (with bi-directional control) and command the blower motor speed. If that works there could be a problem with communication between MFD and the air-conditioning amplifier, but I wouldn't replace the MFD without checking the communications stream between MFD and Gateway ECU (which commands so many other functions as well) and between the Gateway ECU and Air Conditioning Amplifier. If the compressor itself works - you can hear it operating, if set to MAX COLD with A/C on - I would doubt that there's a problem in this chain of communication.

The lights on the Combination Meter - A/C AUTO, Recirc, and front and rear defog - are also commanded by the Gateway ECU; if they all follow the indicators on the MFD, and the MFD's indicators match what you press on the steering wheel, I can't see how anything's wrong in there. The steering wheel switches are connected directly to the A/C Amplifier, so the flow goes the other way (A/C Amplifier to Gateway ECU to MFD).

If the blower still doesn't operate at all, the next step is to connect the battery supply directly across the motor itself. If it still doesn't spin, you need a new blower motor. MSRP is $141.08, Champion ToyotaWorld offer it for $107.60. The blower motor is part of the heater core, behind the lower glovebox, but I'm not sure if it's accessible through that route.

If the blower motor is good, the procedure says to check that the blower motor controller is getting the correct voltage, and that the ground connection is good. If either are bad, repair or replace that wire harness.

The next step is to check the connection between the blower motor and its controller. Here we're checking that the connection between motor and controller is good, and that it's isolated from ground. If still no fault found, we move on to checking the connection between blower motor controller and air conditioning amplifier (master A/C ECU). If the waveform from the A/C Amplifier seems to be OK, it says to replace the blower motor controller, otherwise replace the A/C Amplifier. The Blower Motor Controller is MSRP $183.11 while the A/C Amplifier costs $473.69.

However, the A/C Amplifier is in the bulge at the bottom centre of the dash so should be easier to access. Given that I might be inclined to check the A/C Amplifier output first before having to disassemble half the dash to get at the blower motor.

So much of this car is about communication between different ECUs and complex electronics commanding simpler electronics to provide varying voltages for the variable-speed motors. I worry that mechanics are weak in understanding and diagnosing electrical and electronic issues.

 

I worry about that too. I have experience from military and industrial electronics, that glitches can be due to corrosion of connectors, poor shielding allowing noise, etc.

 

I read your posts from April 2009, and I am wondering if you ever got the problem fixed. I am having the exact same problem on my 2007. The touch screen responds perfectly, but no air. This seems to happen on startup, about 15% of the time. Thanks

 

I am having the same issue on my 2006, but I would say more like 5-10% of the time. It happens all different times of the day and outside temps (I live in FL). The touch screen seems to be working correctly and the controls on the wheel do not make the a/c to work either. My issue is also on start-up, but not necessarily after the car has been sitting for a long time.

 

I am having the exact same issue with my blower. When it works it still blows cold air, but randomly it will not work on startup...not ideal in the heat. Any insight would be appreciated...would love to avoid the dealer fix.

 

Just to be clear about this: with the car ON, when you guys go to the Climate screen and manually turn the temperature to min and the fan to max, sometimes nothing happens?

 

Same problem with the blower here on my '07...it has happened twice in the last few months but I imagine having problems duplicating it with money spent at a dealer trying to diagnose it.
I assumed it had something to do with me pressing buttons too quickly during startup, causing some communication problem. Buttons all work, but no blower...then, after driving for a few minutes, it mysteriously starts working!