6HP26 Land Rover Transmission Codes: P0780, P0781, P0782, P0783, P0784 and P0829

So today I got a customer with a 2006 Range Rover Supercharged with a transmission problem. The concern was that he felt a "jerk" when the car was accelerating at a certain speed. So I drove the car and as it changed from 3rd to 4th gear the car would basically harshly shift and when it did you would feel like somebody pushed you from the back. After determining that it was indeed the change between 3rd to 4th hear (is not like it did it once and I knew it was exactly there I'm not that good, but I'm getting there :D) I drove it back to the shop (a bit upset because the car had almost no gas) and plug in the Land Rover computer. Here are the codes that came up:

• P0783-62
• P0783-64

Upon a hours of reading (when there is not much to do I try to read as much as I can) this is what learned:

The following codes are shift codes. What happens is that the computer monitors the input and the output of the transmission to calculate if everything is ok.

• P0780-00: Shift monitoring fault - input/output shaft speed ratio out of range during a shift (any gear).
• P0781-62: 1-2 Shift - Comparison of input and output speed during a shift
• P0781-64: 2-1 Shift - Comparison of input and output speed during a shift
• P0782-62: 2-3 Shift - Comparison of input and output speed during a shift
• P0782-64: 3-2 Shift - Comparison of input and output speed during a shift
• P0783-62: 3-4 Shift - Comparison of input and output speed during a shift
• P0783-64: 4-3 Shift - Comparison of input and output speed during a shift
• P0784-62: 4-5 Shift - Comparison of input and output speed during a shift
• P0784-64: 5-4 Shift - Comparison of input and output speed during a shift
• P0829-62: 5-6 Shift - Comparison of input and output speed during a shift
• P0829-64: 6-4 Shift - Comparison of input and output speed during a shift

You get the idea, the two codes I have were from third to fourth gear and from fourth to third. After further reading I learned the power flow inside the transmission and learned what clutches were in operation during this shift.

Now to the big question: what's the fix? I wish it were that simple, but I came to the conclusion that the fix goes in the following order from cheapest to most expensive.

• For free: Clean the grounds for the transmission computer: this is sort of easy, they are at the right hand side of the engine compartment, all you have to do is take out the hex bolts for the fuse cover, then you'll see a couple of 8 mm nuts holding the fuse bracket, and below that a couple of 10 mm bolts which after taking them out will allow you to move the whole box and undo the two 10 mm nuts which hold these two grounds. Only one of the is for the tranny computer but let's clean them both since we are here! You just undo them, and sand them a little bit with sand paper and put them back tight. Put everything back together. This seems to work like 5% of the time

• For free: from the bottom of the car unplug the transmission connector (a round connector). In my case, somebody had changed the transmission connector and bent the pin, I straighten it up but that didn't fix the problem. Notice in the pic how the top pin is bent. This seems to work like 10% of the time.

• For about $400 dollars: change the transmission filter and flush the fluid. I recommend a high performance fluid not the one that zf uses, even though some forum guys say the zf fluid is alright, this one is a million times better: This seems to work like 60% of the time
• Red Line D6 ATF and the filter: ATP Automatic Transmission Filter Kit.
• If that doesn't work then its time to try more drastic (and expensive measures). For about $1500: replace the valve body. The valve body in these cars includes the transmission computer and solenoids which are subjected to the fluid all the time and go bad most of the time. You could get an estimate at a local transmission shop (I think they are better qualified). This seems to be the case like 15% of the time.

• And last but not least the transmission. For about $8000 dollars a brand new tranny because one of your clutches is worn and needs to be replaced.This seems to work like 10% of the time.