Just started to intermittently hard downshift 2 to 1

Last couple of days every now and then I'm getting a hard 2nd to 1st downshift. She was tuned about a month ago and from then everything has been perfect until now. No leaks underneath whatsoever and trans service was done about 10k miles ago. Could it be low? I've got a dipstick but not all that confident with it... it's black and the tip is very flexible so not sure if I put it in too far and it bends...

My Sprinter was new in 2015, all stock, and when I turn into my driveway it will often downshift --rather abruptly-- into first. Just figured that was normal when going slowly and applying brakes.

How many miles do you have? And what engine?

It's the V6, OM642 (which means it has the 5-speed transmission); now has about 27K miles.

My driveway is a rather steep downhill slope on the way in. I've seen it do that rather abrupt downshift into first there, as well as at other times under similar circumstances: already going slowly (like preparing to stop), headed downhill, while applying brakes. Not always, but often.

I just figured it was a normal part of that transmission's operation, which will downshift any time the brakes are applied and held for more than a few seconds. Continue applying brakes to slow down even more, and it'll repeat the downshift as the vehicle slows.

Going down my long, steep hill headed into town (live on a bit of a mountain), it will hold in that lower gear for a while even after releasing the brakes; apply a bit of power on a flatter area and it'll upshift again. Mostly it's a non-issue (and engine braking helps on long hills), but it does seem to jolt a bit just before stopping if it decides it wants to be in first gear. I just live with it.

Happened to me yesterday. Right to the dealer. The only fault they could detect was the particulate filter was getting plugged. The mechanic told me that is could lead up to the transmission issue. They cleaned the filter and no issues. All's well. Have extended warranty. no cost.

I have 2015, 144", 44k Miles.

Hmmmm... When I had my DEF issues a year ago, the tech not only changed both NOx sensors, but also the DPF..... probably less than 9,000 miles since then....

Dennis? Any thoughts?

On my 2008 OM642 V6, I had this same issue. Random hard downshifts. Turned out to be a stuck butterfly valve in the EGR. Took apart and cleaned it and problem went away.

Also started using BG244 diesel fuel additive. I add one bottle every year and I clean the EGR valve every year at the oil and filter change. Problem has not resurfaced since performing this maintenance.

Driving habits, long idles will soot up the butterfly valve. Anything under about 55 mph I keep out of 5th gear and I avoid any unnecessary idling.

I clean the EGR on my Jetta TDI about every 5,000-8,000 miles. It's not hard, just a bit messy... How is it in the OM642?

Its not difficult to take out the EGR valve on an OM642 and clean it, just takes some time. The first time I removed it it was a bit tricky getting it out because I suspect it had never been removed even though my van only had maybe 18,000 miles on it at the time. The valve has a cylinder that sits down in a housing bore with a clearance that is quite small. So if there is any accumulation of soot in the bore clearance it makes getting it out somewhat of a chore. I found that by removing the 4 bolts and then by rotating the valve helps to break up the tight fit so that it can be pulled up and out. When you clean the EGR be sure and clean the outer diameter of that bore as well as the bore receptacle that stays in the vehicle. That way the next time you remove it it will hopefully be an easier job. I used carb cleaner to clean mine with a small brush. You can soak it in a pool of cleaner and let it soak for a while between brushings. You can also reuse the gasket as it is a metal gasket that can be used over and over again. After you think you have it clean enough rotate the butterfly valve and make sure it springs back to the closed position in a well defined and smooth action.