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Discussion Starter · #1 ·
2009 Touring Model, 3.8L, 6 Speed AT
Manual Temperature Controls (Front and Rear; Rear controlled from second row overhead console controls)

Symptoms: Blower running, A/C engaged or not engaged, vents in any selection ("face", "feet", bi-level) regardless of outside temperature or humidity, and the entire HVAC System will reset (mode door will go to defrost and full heat for about 55 to 60 seconds or so) completely randomly.

Manual Temperature Control with separate temperature control available for the back (if selected). I have narrowed it down to a really weird circumstance after recording all the various settings and conditions when it occurs. It is somewhat repeatable, but mostly occurs randomly.

The van can be in park, neutral, or drive. A/C on or not on; vents on "face", bi-level, or "feet" - doesn't matter. The HVAC system doesn't even to be on for the reset to occur. When the throttle is advanced past idle speed to approximately 1500-2000 rpm, the system resets.

If the HVAC "head unit" is on, the lights flash on the buttons (they go out for approximately one second, then come back on). Then the HVAC goes to windshield defrost mode, and turns on the heat (mode door moves to full heat position). This whole "cycle" takes approximately 55 seconds to 60 seconds.

The engine does need to be running for the issue to occur. If I shut off the engine while the symptom is repeatable, then moving the throttle has no effect on the HVAC system. It continues to operate as normal (in this instance - blower on, no A/C, "face" vents selected). Once I restart the car and the idle settles down, the symptom can be repeated again with regularity.

After reviewing the W/D, the only common point in the system is the TIPM. How in the world a spurious signal from the throttle could ever affect the HVAC is strange as the systems are not on the same bus and are separated by the TIPM. I am looking into further analysis as it happens, but whenever I take my WiTech out to it, it won't mess up when I am watching it.

I intend to put a scope on the IHS bus so I can see what is happening to the bus when this occurs, but I will need to see it happen at that time as I don't have a DSO to use (I have an old Fluke 123).

Anyway, it has been months since this started, and it is random when it does start happening, but when it does, it is very repeatable. I have ruled out the upper controls in the overhead console as I have unplugged them when the issue occurs and the upper controls have no effect on the symptom.

Also, I can have the A/C button off (using only blower motor and outside air) and the issue can still happen. I talked about this in another thread, but I think this one needs a new thread since the OP of the other thread has disappeared:

 

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Discussion Starter · #2 ·
Also, since I posted in the other thread I would check it over the last weekend, the symptoms have not come back. Therefore, I can't test it since the issue is not occurring. Doesn't seem to matter about bumpy roads, jostling the center console, etc. If it starts acting up again, I will start the troubleshooting again. I'm quite sure the issue will resurface.
 

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2013 Dodge Grand Caravan
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Aside from the whole throttle interaction, it sounds like a defective HVAC controller. Have you tried that already?
 
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Discussion Starter · #4 ·
Not yet, that is first on my list of three things to test and change (based on cost order):

1. HVAC controller
2. Throttle Body
3. TIPM

I really want to see the failure occur on my scope so I can determine if it's IHS related, but at this point I think I just going to start throwing the parts at it - lowest cost to expensive.

It's a little tiring not knowing if it's going to work properly or not when I'm traveling. Nonetheless, I enjoy the challenge!
 

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Discussion Starter · #5 ·
Well, got two of the three parts. Got two TIPMs and one HVAC controller. Got the two TIPMs because there weren't terribly expensive, and finally found an HVAC controller (not too easy to find). Haven't had the issue occur since my last post, but I'm getting ready.
 

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Discussion Starter · #7 ·
Okay, finally caught it when it acted up. Had a test light set up to see if I lost the fused ignition switch output in the TIPM. It is not switched off in the TIPM. So the reset must be coming over the CAN.

I have determined that power loss is not the issue and is not causing the reset. Also, I have confirmed that power loss does not cause the recirc button to turn off, only the "reset" command the HVAC Module is receiving.

Progress!
 

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2013 Dodge Grand Caravan
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Is that with the new HVAC controller? I'm thinking the problem is internal.
 

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Discussion Starter · #9 ·
So, I was able to get the issue to occur multiple times in a row, so I hooked up my wiTech and started watching a bunch of PIDs. Although I wasn't directly on the bus (looking at the HVAC controller through the TIPM), I was able to see that the RPM for some reason is read by the HVAC controller. Long story short, I'm replacing the HVAC controller first and I'll see what happens. This will be tomorrow or Friday.
 
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