I have a 06 XL with 186000KM and a 4R70E transmission (according to Etis). Recently I have started getting hard shifts from first to second gear. It doesn't happen all the time but more often than not it occurs when the engine is cold and/or I'm turning right. It doesn't seem to be slipping, just staying in 1st longer until it finally shifts hard. I have been slowly changing the ATF using the pan drop method and the problem has not gone away or become worse. Doing some research it seems the likely suspects are:

1. Sticking or damaged check ball-valve
2. Sticking 1-2 shift valve
3. 1-2 accumulator leaking or binding
4. Faulty shift solenoid

How should I check these? Are there any other things that might be causing this?

 

Could be a TPS sensor issue on the throttle body. I'd go ahead and replace that first before I decided to tear into the tranny.. You can ohm out your old one to see if it is providing a smooth signal..

 

Am I looking for dead spots or just a smooth curve?

 

Smooth is want you want, any jumps or dead spots is an issue..

 

OK, I took a multi-meter to it and the resistance of pin 1 and 4 are opposite of each other. When the throttle plate is wide open one measures a very low resistance and the other shows a high resistance. Now I'm using a cheap multi-meter with a low refresh rate but it seems to change smoothly. The stepper motor that actually moves the throttle plate seems to make an odd clicking sound when in anything but idle, could this be throwing the sensor off?

 

(Sticking throttle body)
Its possible.. There is actually an additional TPS sensor on the motor of the throttle body. It is just a microchip that reads from a magnetic tone ring.. The 2 TPS sensors work together, but it's more Likely that the one bolted to the throttle body will fail.. Is the throttle body clicking when actuated manually? Or electronically?

This only happens on a cold motor, but does it go away on a hot motor?
The symptom showing up while turning may be a sign of low fluid.. When was the last time you changed the filter?
Was there any big particles on your magnet when you dropped the pan last?
You should always warm up your vehicle after a long rest prior to driving, even on a hot day...

 

The throttle body clicks when actuated electronically, but doesn't seem like its sticking. When its clicking if you touch the throttle plate you can actually feel it when it does it.

The hard shift happens intermittently whether the motor is cold or warm, it just happens more often when its cold.

The filter was changed less than 6000Km ago (a month, month and a half at the longest) when I added a drain plug ( thanks for the write-up btw.

The fluid shows as full on the trans dipstick when I checked after reading a post that mentioned that might be the cause.

As for the magnet it was covered completely in superfine particles, but given what I know from previously owned vehicles it has the expected amount for the mileage.

 

Do you get any random stalling?

 

Nope. Aside from some slight alternater whine, and a mileage reduction that I attribute to the FX4 wheels it runs like new.

 

Alternator whine huh.. Have you checked what kind of voltage your getting out of the alternator?

I still don't think it's the transmission itself if its intermittent..
What fluid are you using for your flushes?