Solved 4HI Engagement Issue While Sationary (Mostly)

When I first got my new truck in March of 2018, I could sit stationary and click in and our of 4HI with no delays or clunks. However, this last winter I started to notice that more and more that when engaging 4HI while stationary, that the MIL light would continue to blink and I could not get engagement until I rolled a little forward or backwards. I would also sometimes get a clunk when disengaging 4HI. I was at around 6K on mileage at this time.

I was hoping it was just the cold temps that were causing it, but once it warmed up this spring, I was still intermittently having the same issue with engagement, although maybe a bit less. Brought it to the attention of the service advisor at my last "check up" and he said it was normal. Surprise, surprise.

A few weeks ago, with 12k on the odometer, I drained and refilled the front and rear differentials with Redline 75w85. The fluid in both diffs was pretty dark, and there was a fair amount of sludge on both drain plugs. After doing the drain/refill, I can now routinely engage 4HI while stationary again, so it appears the issue was due primarily to sludgy diff oil.

It should be noted that I will still get a clunk when disengaging sometimes, especially if the front wheels are cranked, but it doesn't seem unreasonable for this to happen if the engagement surfaces are under load, I suppose.

I should also note that when engaging/disengaging while rollling, everything always goes smoothly. It would appear that going in and out of 4HI while moving is likely easier on the 4WD actuator, and should be the preferred way to do things.

Just thought I would pass on this bit of information to those that are dealing with the same issue.

 

Yep, normal. It's the luck of having everything just happening to line up just right for a smooth engagement, or having to move a little to get it to engage.

On the old Gen1, I'd often hit the 4-hi button while waiting in traffic or such to make sure it still worked. It was the crap shoot of thirds on if it would engage smoothly, with a clunk, or not engage and need a little movement. Seems the same on the Gen3.

Coming out of 4-hi would be the same.

 

Sounds perfectly normal to me. I'm at 63K and it works just like you describe. Haven't changed the Diff oils yet.

G.