Hi guys, I'm after a bit of advice from the transmission folks. I have a ZF6HP21 in my 335i with 100,000km on it. I have just given the valve body an upgrade with a Sonnax zip kit, new ZF solenoids, new separator plate and replacement mechatronic seals. As well as new ZF Lifeguard 6 Fluid and transmission pan, as I was having a few harsh shifts and delayed engagement in gears 5 and 6.
The car is all assembled again and the transmission has been filled using the ZF procedure, adaptations have been reset and there are no fault codes in the DME or EGS. I backed the car out of the driveway and selected drive and there is no drive at all in foward, it seems to engage in foward momentarily then disengages and goes back to park. However reverse still works normally.
After reversing it down the road to turn around and back into the driveway, Ista D and INPA both show no faults in any of the Ecu's, transmission fluid level is normal, all the solenoids function normally on INPA, the valve body passed all of its vacuum tests before reinstallation. The Air test of the clutches was satisfactory. I am currently suspecting an electronic issue with the TCU however with no faults logged it's proving to be challenging to diagnose.
If anyone has had a similar issue I'd love to know what your fix was, or just some guidance on where to go next, as I'm at a bit of an end now, if I can't find a fix soon it may have to go the gearbox specialists for a complete strip down and rebuild.
