yes, thanks pukas for updating us on your findings, now someone else that has this same issue will be able to find his solution easier. Or in the least get them going in the right direction :o)

Thank you pukas84.
It is always good to hear the results and solutions...good for those who have been generous with their help and good for those who might have a similar problem in the future.
Thank you.

Ok, I know this is a very old thread. Didn't want to leave this thread unsolved. But I finally got around in fixing this issue. I had another 19' lift where the steer cylinder was leaking fluid from the seals. So I took the steer cylinder from the one that wouldn't drive and steer at the same time and swap it. It still wouldn't drive and steer so I now narrowed it down to problem with the cylinder. I took it apart, the rod was slightly bent. Replaced the rod and all is good.

any update on this topic?
i have same issue on my lift
didnt test pressure yet, but hydraulic steer cylinders were recently rebuilt.
i suspect it is either counter balance valve or a diode..

I totally agree, Buy from Skyjack. In fact, Sky jack is usually cheaper than aftermarket. And, quality. Same with Genie, they are always cheapest source of parts, consistently. They offer all manuals online, free. They give support. Why mess around with cheaply made aftermarket parts that will fail soon after. The cheap switches and controls actually cost way way more when they fail. Labor and lost time to re-fix bad quality parts.

he would be better off buying parts from skyjack
totally NOT recommended to buy aftermarket parts for these machines

If the joystick is bad,you can purchase from me.I am the joystick manufacturer from China.I can offer you best quality and price.The delivery time also can short in 2 weeks.Please feel free to contact me.E-catalog and sample is available.

I found this thread online because I was having a similar issue. I ended up getting on the phone with Skyjack and told them the issue I was having (unit would steer fine on steer only function). If trying to steer while driving, the front wheels would only turn about 3 degrees.

Plug your test gauge into the test port on manifold. Drive the machine and observe the pressure. On a firm level surface you should have 500psi. If its considerably lower, you have a bad counterbalance valve, which regulates your pressure. If it stays the same, activate steer while driving and observe the pressure guage. If it drops considerably while steering, your steer cylinder is bypassing; If pressure stays the same, your front steer spindles are bound and drive pressure (500psi) is not enough to steer them as opposed to standby pressure (2400psi) <- this was my issue.

Hope this helps.

ok using the serial number you provided the test proceedure is basically the same except you use the lift function on the ground control, raise the unit to full height and take a pressure reading and then set the pressure according to the data on the dataplate on the lift. The dataplate/sticker should have the hydraulic pressure listed on it.
if you cannot get it to achieve the correct pressure then you may have a faulty relief valve or a worn out pump or a bad steer cylinder packing.
checking the steer cylinders is fairly straight forward, get a bucket to catch the fluid, steer it to one side, then remove the line from the one side of the closed end of the cylinder and activate the steer direction and check for any bypass fluid, there shouldn't be much coming past the packing. if you get alot of flow with any pressure behind it then its bypassing, bad packing. You can try to repack the cylinder but check the cost of just replacing it, it might be more cost effective to just order a new cylinder. (replace both cylinders, if one is worn out the chances are the other one is too).

Serial number is 22017476

first... a serial number of unit might help get the right service manual. But with that said you need to get a 3000psi hydraulic test guage.
Look on the hydraulic manifold block, it should have a quick disconnect test port to connect a guage to. Also locate the system pressure relief valve at R1 on manifold.
Now with guage in place, press and hold right steer and let system stall out, take a reading on guage and then release steer button. The pressure should read the rated relief pressure for this unit which should be around 2150 psi. If you do not get this pressure reading try and adjust pressure on relief valve to get this pressure reading.
If you DO have correct reading then i would start looking for a bad steer control valve or a bad cylinder, worn packing causing a bypass in cylinder might be your problem or possibly a faulty steering valve in manifold block.

I'm basing my information on older machines ( i used the oldest serial number range in skyjacks manual list ) Newer machines may be different. You can go to skyjack. com and find your manual as well, they are open to the public ;o)

So whats that serial number?

check your diodes one is loose or bad.

mrbob I see you are in hawaii, where are you located?

Well by golly, you're issue sounds exactly like every old SJ3219 I ever worked on!
Don't waste your time. Drive it, does it steer? Bob's you're uncle ;)

You need to run a pressure test. The steering does not require a lot of flow but it does require quite high pressure. You might have a pump that is getting weak.