Hi folks,

Looking for a bit of help or shared experience on this one.

I’ve got a 2009 facelift TDV8 (digital dash) running the ZF 6HP26X box. Gearbox was always smooth apart from a slight judder in 3rd, so I decided to give it a full service — fresh ZF Lifeguard 6, a genuine Filtran plastic pan/filter, and new mechatronic seals.

When I bought the car, it already had the metal sump and separate filter fitted, so this was my first time switching it back to the proper Filtran setup.

⸻

The issue

After the service it drives spot-on for about ten minutes, then I get:

“Gearbox Fault” and it limits to 1st 2nd and 3rd Gear.

The only code showing now is P0735 – Incorrect Gear Ratio (5th Gear).

If I restart the car, the fault clears instantly and it drives fine again until it warms up and shifts into 5th.
If I keep it in manual mode (1–4) it’s flawless.

Level was set correctly — hot fill at about 38 °C, engine running, steady dribble — added roughly 5.5 L total.

Has anyone had 5th-gear ratio faults that clear on restart after a fluid and filter change?
Wondering if this points to something like pressure loss, air in the system, or possibly an internal seal issue that’s only showing up once hot.

Would love to hear from anyone who’s had similar behaviour or ideas on what to check before I drop the pan again.

Thanks
Liam

Certainly classic symptoms of a worn rear stator bush, but starting immediately after a fluid & filter change seems unlikely. Did you change both the bridge seal and the four jump tubes?

Are you able to read the clutch adaptions at all? The measurements for the E-clutch might provide a clue as to whether the stator bush is an issue, otherwise it would mean removing the Mechatronic unit again and testing with air pressure.

Phil

Don’t think I have any way to read the clutch adaptations, I was thinking it could be the rear stator bush but was also baffled as to why it’s started after a fluid and filter change. I changed the four tube seals the double square looking one and the connector sleeve.

That along with it being absolutely fine in 4th or does it not affect 4th as much?

Traditionally, a worn rear stator bush manifests itself by the transmission refusing to engage gears 4, 5 & 6 i.e. the three ratios which use the E-clutch.

Generally, therefore, the transmission shifts through 1st, 2nd & 3rd gears but then refuses to upshift into 4th.

If you calculate the torque being transmitted by the E-clutch, in 4th gear it’s 72.6% of input torque, in 5th gear it’s 125.5% and in 6th 100%.

Theoretically, therefore, it will begin to slip in 5th gear first.

I agree that this is far from conclusive, though, and still doesn’t explain the relevance of the oil & filter change. All of the pressure solenoids are electrically ‘off’ in 5th gear, so it doesn’t really sound like a solenoid issue, either. Pressure loss combined with temperature dependency does point towards a leaking internal seal.

Phil