Climate Control not responding - no negative CAN voltage to HVACCM

Brandon Schmitz · Mar 29, 2020

Yesterday I lost all control to my Climate system. None of the physical control panel inputs work, and the screen is frozen on OFF, even though it's still running and blowing.

Code U0164 present.

Found this video, these are the EXACT symptoms. I checked the voltages suggested and I am NOT getting voltage on the WHITE CAN (-). Fuse (+) and (-) are good, as is the 2.6V CAN (+). Anyone know where to work that signal back up to in order to troubleshoot where the short might be? I've done general stuff like wiggle the wire in the connector to make sure it's not loose, and general cable wiggling to see if i could get some voltage at the pin. I also went through all the fuses that either said HVAC or sounded somewhat related.

Also, I recently installed a cabin air filter kit. I can't imagine how that would have any impact on this, but seems pretty coincidental.

Any resources or ideas for troubleshooting the CAN (-) would be much appreciated.

rojo_143 · Apr 1, 2020

Did you get this corrected yet? If not I recently had this happen on my 2018 qc 1500. Took it to the dealership sonce I am still under warranty and it end up being a bad ground connection behind the radio where the wire came loose from the terminal lug.

Loudram · Apr 1, 2020

Yep, a loose or bad ground can do all kinds of crazy stuff to modern cars.

OCDTech · Apr 1, 2020

@Brandon Schmitz When you measure can with a volt meter you will get an average voltage, not accurate. Need a scope, really expensive, i've been looking into them.

Four things can cause No comm with modules.

1 Open can line
2 Shorted can line. ( broken touching ground or power. Or a bad module, not just the one its affecting. Any bad module can affect can bus. ( the link has an example of this.)
3 No power to module. ( you seem to have that since its frozen on.)
4 No ground, like one said above, I would check this first.

If you have time, watch a lot of Diagnose Dan on you tube, super smart guy on can-bus. Although most of his stuff is european, still can though.

a good explanation. Personally i suspect broken or shorted can bus line last.

Brandon Schmitz · Apr 6, 2020

OCDTech said:
@Brandon Schmitz When you measure can with a volt meter you will get an average voltage, not accurate. Need a scope, really expensive, i've been looking into them.

Thanks for the link @OCDTech , agreed on the "accurate" comment, but even with a DMM, the value will bounce between 2.2 and 2.4 volts for (-) for example, indicating that you are at least getting a signal. I was clearly seeing ~2.6V on the IHM(+), but the negative was not seeing a signal at all. I was tracing through the system to find where that signal was getting lost by checking all the connectors at the BCM, Diagnostic Connector, Star Connector and the AC Control Unit. Everything was checking good.

After exhausting all my wire wringing and troubleshooting I bit the bullet and took it to the dealership. They troubleshot and isolated the A/C Control Unit (the center stack, not the Control Module in the glove box). Replacing it resolved the ground circuit issue. Parts for 2015+ with the automatic dual control are crazy expensive as others are finding. $390 for this unit, ~$450 for the Control Module. Plus the hundreds they charge to get tools out...this was not a cheap one.

Climate Control not responding - no negative CAN voltage to HVACCM

Brandon Schmitz

Junior Member

rojo_143

Senior Member

Loudram

Just a sinner saved by grace

OCDTech

Senior Member

Brandon Schmitz

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