Thread: 2011 D4 'Gearbox Fault' warning

Hello Easter Bunnies

With 4 days off to eat chocolate eggs and work on the Disco between swims with the kids, I figured I'd start troubleshooting some "Gearbox Fault' warnings I have had that put the car into Restricted Performance mode.

Backing up a bit, my 2011 D4 started behaving badly in December with a few Gearbox Faults popping up on the Xmas migration north and back home again. The faults have happened a few times since almost always on the highway and it seems always when the engine is coasting under load (up a slight incline for example) and needs to shift down. The 1 exception was the very first time it happened, pulling out after refuelling into crawling traffic up a hill. I did not notice whether this happened shifting up or down. Pulling over and restarting the car clears the fault and returns performance to normal. I'm ashamed it's now easter before getting on to it.

I have read a few threads which have been helpful but thought I'd start my own to help as I decide to DIY or book it in for more than I can do myself.

Symptoms and general observations so far:

• Driving around town I have not had any gearbox faults but there is some slight shudder when in D and I suspect (although I might be wrong) only in 3rd gear. This only seems to happen up a slight incline. Shifting to S seems to stop the shudder.
• In similar driving circumstances I suspect the torque converter occasionally slips. The tacho needle briefly jumps and the car surges. This kind of feels like slightly pushing the clutch on a manual car when driving. The surges are about 1 second apart and seem like they would go on indefinitely, or at least as long as the incline. Shifting to S seems to stop the surging.
• Highway driving in D, again, up a slight incline almost inevitably faults. As the revs drop to about 1500 and I start wondering when the change will happen, the fault occurs. The same driving conditions in S almost entirely eliminates the fault although it has happened in S on 3 occasions.
• Gear changes at any speed are pretty smooth and there is no delay engaging gear when selecting R or D from P.

I read somewhere that the gearbox fault can occur during a bad shift like the 1500ish RPM shifts described above. I also read that the bad shift could be caused by low transmission oil, badly degraded oil, or misbehaving valves or seals in the mechatronics unit.

My first task today was just to check the fluid condition and level. I had 1.5 litres of new Lifeguard 6 so I drained the oil and refilled (following Robbie's guide). I refilled using a mix of the old oil and the 1.5 litres of the new. The old oil is dark but does not smell burnt. When wiped on a white paper towel there is no colour on the towel as the oils soaks in. So it looks like I'm ready for a change but it doesn't look like the oil has been cooked. After adding the 1.5 litres of new oil I had 750 ml of the old oil left. So I guess I was low by about 750 ml. I drove the car and the changes are smooth. I still noticed some very slight shudder in 3rd. I have a tube of Lubegard instant shudder fixx but I'm holding my guns on that for now.

I have not yet driven it on the highway but I think it's a stretch to imagine the faults won't continue to happen. Assuming I'll still get the faults the next idea is to do a proper transmission oil change (not a full flush) and change the solenoids and seals in the mechatronics unit. Seems super easy to do but at $500 or whatever worth of oil, plus new valves, seals and a gasket at a minimum I'm wondering if I'll get any change from $1500 without having addressed the torque converter. Yes, cheaper than a $7K rebuild, but not if I eventually find a rebuild is required anyway.

Changing the solenoids etc is an easy enough DIY but I'm not so sure I want to drop the gearbox myself.

I'll update after more driving but if anyone has any thoughts or similar experience, I would be very happy to hear your tales.

Thanks!

Thanks DiscoJeffster. Watching vids now. I thought the Discovery was build around the heater matrix. I'm now thinking the D4 was build around the HPFP. Looks like a long day.