Scanning for U codes.

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06 Escalade. The rear heat stopped working. Unfortunately the control module at fault was discontinued so I went with a new aftermarket Dorman product. The heat is back, blend doors work, but the fan now has a mind of its own. Blows after shutting off engine. Blows on high, rather than slowing to a stop reaching desired temp. I contacted Dorman about this, they asked me if I had any body control module codes. U codes. I was unable to answer whether or not i'm "communicating with the BCM". Until i can answer that they won't exchange or refund me. I have a innova 3040d that reads odb2, abs and oem enhanced codes. I've seen brake switch codes, transmission codes, things that are deeper than odb2. but I've never seen a u code/BCM code or however they are referred to. So my question is do I need a special scan tool/reader to see these codes, or should a decent odb2 code reader be able to display these.
 
I have a 2000 Deville. Recently I had a module problem and went to the Cadillac forums to try and diagnose it. Turns out there was a a sequence of buttons to push and hold that would give a comprehensive sequential dashboard readout of module status and communication codes, to include U codes. My OBD II reader won't even begin to cover what the on board system revealed. I suspect your Escalade is similar.

Check Google and Cadillac forums before trying any outside diagnostics. If it's like my car, on board diagnostics for the overcomplicated system are extensive, and aren't covered in the manual.

My problem ended up being a bad Rear Integration Module. Also a discontinued part. I ended up finding a "new" unit on ebay from a company that bought up excess dealer stock.
 
where did you purchase this from? You should be dealing with the vendor about the warranty on auto parts not the manufacturer
 
Originally Posted by LeakySeals
Blows after shutting off engine.


This is a clue as GMT-800 platforms never had "afterblow" that I'm aware of, This could be the Auxiliary Blower Motor Controller OR the Auxiliary HVAC Module you got from Dorman is faulty or configured wrong.

I guess the first thing I would do is......
*Lets not use the AUTO OR AUX settings on the FRONT AUX control panel for now....Use the manual speed adjustments!
*Try to control the AUX blower speed with the FRONT AUX control panel as it is NOT a serial data device & is wired directly to the HVAC module.
*Do you now have full control of the AUX blower?



IF the blower still has a mind of it's own, Using a DVOM, Hook the "red lead" to a 12 volt power source......
*Locate the Blower Motor Controller (It's right next to the blower).
*Locate the Small gauge purple wire & either backprobe it through the back of the connector or strip about a 3/16" piece of insulation off the wire.
*Hook the COM lead to the small gauge purple wire.

At high commanded speed.....The DVOM will read @ battery voltage.
At half commanded speed .....The DVOM will read @ 1/2 battery voltage.
At low commanded speed......The DVOM will read @ 2.00 volts.
OFF will display zero volts.

****If the Blower motor runs at ANYTIME the voltage on this circuit is at zero......The Blower Controller is faulty!!!!
****If you have voltage on this circuit ANYTIME the key is in the off position......The HVAC module being defective is a High possibility!







More information about this circuit.......
*The small gauge purple wire IS the control circuit from the HVAC module to the blower motor controller.
*The signal sent on this circuit is actually PWM but a DVOM isn't fast enough to read Duty Cycle.....It will just read an average voltage.
*You "can" the DVOM common to ground & hook "red" lead to the control wire, BUT this will INVERT the expected values. This tends to confuse people that don't do circuit testing on a regular basis.


I highly doubt a Class 2 serial data issue would cause the blower motor to act the way you describe as I've never seen it myself, But without a capable scan tool it's a guess on my part!
Dorman IS junk, So it's natural to suspect any product they sell.
 
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