Fans not engaging, voltage dropping badly when they should be

[Marcus567]

I have a 2005 Yukon XL Denali, problem started with charging system failure message a few weeks ago, i noticed the serpentine belt tensioner was bad, belt was loose, figured that would explai temp creeping up and voltage drop, changed the tensioner and problem seemed to go away, week or two later, noticed a leak, found what I thought was power steering lines leaking, a week later noticing coolant low, chargin system failure message coming back, but only when idling long periods, two days later died at an intersection, battery dead, junkyard tensioner that seemed good shot, so got a new tensioner, charged battery, problem still happening, tore into it today, found radiator was cracked near oil line fitting, fans not kicking on at any temp, and voltage starts dropping right at 203 degrees, checked fuses, relays, put ground to relay wires, fans operate at all three speeds, checked relay wiring to fuse box, checked pcm wires for corrosion, battery tested good, alternator charges fine with coolant temp sensor unplugged, and both fans running, surely with as common as the radiator crack is someone has had this fan issue before. Any help would be appreciated.

 

[Joseph Garcia]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

I cannot personally help you with your question; however, other members on this Forum that are much more knowledgeable than me in this area will chime in.

 

[swathdiver]

When voltage drops at the point where the fans should be coming on, this tells me that it is a high resistance issue. Does that mean a fan motor is bad or a ground is bad? That's where I'd check again. I don't have your troubleshooting guide, you can get it for about $20 at AllDataDIY.