SOLVED! Fan 1 comms error

[Mooseman]

The money light is on and it's a U0632, lost comms with left cooling fan (yeah, the fans are on the network!). Tried to disconnect the fan to do some diagnosing but I just wound up finding a feral cat under the hood. As best as I can diagnose, I figure it's the module in the fan that's borked as it also threw a U1345, LIN Bus communication fail but after I pulled the fan's fuse and reinstalling it, that error disappeared, leaving me with just the fan error. The only way I can disconnect the fan is to remove them so I may just shotgun it if I have to do that.

I was eventually able to disconnect the fan and check the voltage, ground and the LIN Bus wire for data with a small scope I bought on Amazon. All were good except the data line showed a different wave form than what I have seen on the Net.

Normal:

Mine:

 

[Mooseman]

Just reposting here for the Google bots and in case anyone else has a similar issue with hopefully a resolution.

Yesterday, I replaced the "defective" fan on the Sierra. Was not an easy task. I was able to do it without taking out the whole radiator/condenser/cooler assembly that the book said. I was able to separate the fan assembly from the radiator and tilt it back enough to squeeze the unbolted fan through but I did have to move the radiator forward using a ratchet strap. The new fan does look like it was updated.

So reconnect the battery, start it up, all looks good. No money light. But on second restart, it's back on . Scan shows the same codes it had before (U0632 (fan 1 communication loss) and U1345 (LIN Bus 1 communication error). When I clear the codes, only U0632 comes back up. A bit of research and possibly something else on the LIN Bus is putting garbage on the network or it's a wiring issue even though I checked the data line with a scope. I'll have to check again by unplugging different modules on the network and see if the network traffic changes or that code goes away. Supposedly the active grille shutters are usually a suspect.

Stay tuned.

 

[Mooseman]

As you see from the thread title, I finally figured it out. It was one of those expensive

Tore everything apart again with plans on how to test this. I unplug the fan and active shutters, I check the network signal at the fan and it's still garbage, worse than the pic above. (sorry, no pic, too sunny). Then check the signal at the shutters and it's as it's supposed to be. Check for continuity on the LIN Bus from the shutters to the fan, nada.

Start tearing into the wiring after taking the wheel and felt wheel well off. When I checked the wiring the first time, this is what I saw:


After I removed the PCM and air filter housing, I moved the fan wiring and connector like this to better check it. Saw this:


Might not be visible in the picture but there's green pus around the break in the loom (circled)

So I peel off the loom, and as Eric O. would say, here's the money shot:



So now I setup to patch the wire. Had to add some wire, soldered and used double walled with adhesive shrink tubing:



Finished it off by wrapping it twice in anti-rub cloth tape, cover it up with new loom, and tape the snot out of that T split:


Get it all back together, start it up, scan and no codes!

I think that a combination of skimpy wire and over-routing and zip-tying, putting strain on the wire. It broke directly under a mounting zip-tie.

So for anyone reading this, thoroughly check your wiring. I could have had essentially a free repair.

 

[mrrsm]

Automotive Oscilloscopes... FTW!

For those in similar circumstances. THIS Tool Kit will become invaluable:

https://www.amazon.com/dp/B0D17ZL83R/?tag=gmtnation-20