After purchasing my car and experiencing random gearbox faults, I had my indy change the filter and drained the system 2 times. All was well until a few weeks ago. My state emissions check came due, so I took it in to be tested at a local GMC dealership. The procedure requires the front wheels to be driven onto 2-3 foot high ramps which I assume lets the tech look under the car. It passed which tells me there were no active codes at that point and the tech then started to back it off the ramps. As he started to reverse, I could hear the motor at a high RPM like something was holding it back. Finally, he backed it out of the bay and shut it off. When I got in to restart it, there was a gearbox fault and a yellow engine light on. As I have done in the past, I restarted the car to clear the fault, but it didn't work. I drove in limp mode (about 10 minutes) to my indy who scanned the codes.

606-TCM "watch dog" circuit malfunction
730-gear ratio fault
736-reverse gear ratio fault

He reset them all and there were no issues on my ride home. The next day I started to notice hard shifts into 3rd and sometimes 4th in sport mode (normal setting for me). These resulted in a couple of gearbox faults that cleared on restart. I returned to the shop and asked him to recheck the level of the transmission while changing my oil and filter that were due. He added 1 quart of tranny fluid which surprised me. At that time the codes were:

735-5th gear ratio fault
784-4-5/5-4 gear load fault

He cleared them and test drove it in non sport mode without issue. I drove it home, but the next day in sport mode it started again. When in non sport mode it happens less and when shifting manually even less. Also, from a stop and going up an incline a gearbox fault is almost guaranteed. Yesterday it started happening more in manual and after 2 or 3 gearbox faults, the yellow engine light returned. The code read today:

783-3-4/4-3 gear load fault.

Any thoughts?

Please let me know if the code descriptions are wrong. I found them online.

 

Morning bump.

 

I'd start by getting the fluid level checked as it seems to be related to inclines, hopefully it may be that easy.

 

Hang on norri, it says in the description -

I hope the mechanic knows the specific ZF filling procedure !! And the specific fill temperature for this box .

May be some air pockets still in the system or aeration in the oil . From the low fluid leval .

 

How old is your battery? Borderline and dying batteries are infamous for causing random and spurious ZF gearbox faults....

 

Also double check the reluctor/ABS rings on the rear axles/hubs. If they are not completely solid with the axles, i.e. rotating with the wheels, the trans gets confused as to the road speed and throws these incorrect ratios.

 

Yes, the indy knows the procedure and confirmed with me that it was done correctly. The air pocket theory is an interesting one. Has anyone heard or experienced this before?

I was thinking of having them drop the pan to see if there were any particles in it.

 

Battery is new, purchased last year.

 

Will check that tonight.

 

"May be some air pockets still in the system or aeration in the oil . From the low fluid level"

Is this a plausible explanation? I searched the topic, but really didn't find much on any type of transmission with this happening.

 

I think it's clutching at straws, I don't recall anyone having problems after a drain and refill.
Even though the battery is new you should make sure it's fully charged just to eliminate it.

 

My understanding is that the re-fill procedure does not talk about the need to deal with "air pockets". I seem to remember reading that overfilling it causes aeration/foaming instead. Can you challenge your indy and ask him at what temperature the refill plug has to be closed, just to be sure? Unless there is a leak, you should not need to top it off with extra fluid. Did you check the connector sleeve for leaks? It is a common problem. If it is leaking inside the plug, there could be problems, too. That plug locks with a collar, and need to be secured.

Another test is to go uphill to cause the problem both with cold fluid and with warm fluid. Warm fluid is a lot more runny, so I would expect the problem to be worse warm if this is a fluid level problem...

 

"Another test is to go uphill to cause the problem both with cold fluid and with warm fluid. Warm fluid is a lot more runny, so I would expect the problem to be worse warm if this is a fluid level problem..."

Interesting comment. There are 2 inclines that I take daily from a slow speed after the car is warm. I always get a very hard shift and 75% of the time a gearbox fault. I'm going to have them drain the pan and refill it. I'll also print the level procedure and stress the need to be 100% accurate with the steps. I may even ask to be there.

 

What ATF is in the vehicle? ZF specifies their own Lifeguard 6 ATF for the 6HP26 unit. Many of us utilize Mercon SP ATF (available from any Ford dealership parts counter), far less expensive than Lifeguard 6 ATF and it meets the required Shell M1375.4 specs. If your shop utilizes ATF that does not meet the required specs, that action has been known to create shift issues as well as general performance issues....

 

Used the ZF kit for the pan and fluid, so yes Lifeguard 6.

If I go ahead with the drain and fill, I'm going to switch to Mercon.

 

Did you per chance upgrade to the ZF metal pan (instead of plastic)? There is confusion as to the refill procedure for those and can leave you super low on fluid.

 

Did not upgrade to the metal pan.

 

Update:

The fluid was changed today by my mechanic. Fluid was black and smelled bad according to him. I do want to mention at this time that when they topped off the level the last time, I had them put in 2 tubes of Dr tranny instant shudder fixx which I read about in another thread. Whether this made the fluid black and smell, I don't know. There was no metal on the plug or solids in the fluid. 4 qts of Mercon SP were added back in. The first 5 minute test drive showed hard shifts into 3rd, but no faults or codes. The car then sat for about 30 minutes. The other mechanic then took it out and had no issues and it shifted perfectly during a 15 minute run. When I got there later in the day, the car was cold. I took it for a hard run in sport mode and it was perfect. That was about a 15 minute run. I returned home and came back with my son to get the car (about 20 minutes). I took it the long way home and about 20 minutes in noticed a slightly hard shift into 3rd. Then another slightly harder. 5 minutes later, all symptoms returned. Multiple gearbox faults and yellow engine light on. I was able to clear the faults by powering it down and made it home by manually shifting it through the gears. My thought right now is to either change the filter and fluid or just the fluid again because of what came out. I'd really like to hear other thoughts.

 

Just to add, that fluid was changed last year and I've probably put 2-3k miles on the car since then.

 

morning bump