If anyone is curious about the TDI-Tuning box on the P400, here’s my experience over a longer arc rather than a first-day impression. This is not a full ECU remap which would be the most preferable tune (I have tuned modern V8 SC LR’s with great result but cost is in the thousands) -- but it’s also not just a crappy “Pedal Box” - Pedal boxes only change throttle mapping. This unit modifies engine inputs, which is why the behavior under load is fundamentally different.

I originally bought the TDI box back in 2023. Installed it, drove roughly 1500 miles, and genuinely liked it. Noticeable bump in mid-range shove and smoother response. No drivability issues while installed.

I ended up removing it because I had a dealer appointment coming up and didn’t want any questions or flags with the warranty when they saw the box underhood. Forgot I even had it.

One important hardware note:
When uninstalling it back then, the plastic locking tab on the tuning harness connector that clips onto the boost control valves broke. The OE connectors are robust; the tuning harness connector is not on the same level. I wasn’t forcing it, but the tab failed. I emailed TDI and, to their credit, they sent me the replacement harness free of charge.

Fast-forward to today: Warranty’s over. I found the TDI box in the attic. So I reinstalled the box using the replacement harness. You need to make sure the car is shut down (5 mins door closed, key not near car, hood open) before doing this, btw per TDI’s instructions. Then I drove about 20 miles on the middle setting (4 of 7) to calibrate it per those same instructions, then switched it to setting 6, which they describe as aggressive but not the full “fastest” setting.

After reinstall, everything works as expected. There’s a noticeable power increase (I believe due to higher turbo boost), especially in Dynamic mode with the gear selector in S. Also, It pulls harder in low gears around town or zipping up hills in 2nd/3rd gears -- in normal/comfort and with gear shifter in D or S.

I always felt the stock P400 is slightly weak on highway passing between 70-90 mph, unless it changes up gears and even then, it never really rocketed off. Unsure if it’s aero, the weight of the car or engine settings but -- at those highway passing speeds, faster acceleration is apparent now. It feels stronger. Maybe 10%-15% so?

If I had a quick take on this... something like:

-Performance gain is real, is repeatable. It’s not placebo.
-I monitored engine temps w/ IIDTool in real time before/after and didnt see anything change really.
-Install is simple. Reversible. Undetectable to JLR when removed.
-SO, harness connector quality is the weak point and deserves care and -I don’t know if it’s possible to remove these connectors without breaking them (on the TDI harness side, no damage to vehicle).
-TDI support was solid when I needed it.

One note: I do NOT think you could buy this, and should plan on infrequently uninstall it in preparation for every dealer visit. I don’t see how to undo the TDI-tuning harness-side connectors to the 2 sensors underhood without breaking the clips on the TDI-turning harness. (And yes, I know what I’m doing and all the tricks like pushing IN on the connector, not using screwdriver to force it, etc...)

Long term, I’ve tuned lots of Turbo cars and havent had longevity issues over time. Hoping this is the same. I’m running it at 6 setting, maybe 5 for a nice increase in power - probably won’t run it at 7. In 7, it’s definitely more wild.

Not posting this to sell anyone on it, but there isn’t very much L663 tuning or P400-specific feedback out. I’ll post back up after a period to update.

 

I'd be interested to hear if you're burning off more coolant like the P400's tend to do. Especially over long trips/distances.

 

This is pretty cool. I have been looking into doing some aftermarket tuning for my D90 V8.

 

We shall see... we shall see.

 

Is the TDi tunning box any different than the other throttle controller devices (i.e Pedal Commander) that just shorten/increase throttle by wire pedal travel? Or is it a device that is actually alters A/F mixtures? for a little over 400$ seems very inexpensive compared to COBB, Protune, others. What are the limitations with say modifications to intake or exhaust past oem out the door Stock defenders this would get installed to. Does harness tap into O2 sensors?

 

Yes, it is not remapping throttle (or even connected to the throttle pedal) like a pedal box. On the flip side, it doesn’t re-code the ECU like Cobb.

Classic old school turbo motor tuning in principal: Basically it increases fuel rail pressure slightly, gives the engine more fuel, and lets the motor achieve higher turbo boost. Does not dial back knock sensitivity, etc.
Does not tap into O2 sensors, just 2 connectors underhood that control boost/fuel. It’s a piggyback tune - changes inputs so that turbo boosts higher, But what I like about it all the safety margins/cutoffs (overboost, temp) in the stock engine ECU still apply.

It’s literally like changing out the fuel pressure regulator and cranking up the boost on an old 80’s 900 Turbo. But electronically.

I’ve done the Cobb tunes on a V8 SC JLR motor and the thing smelled like raw gas full time, powerful though.

There’s no customization on this tune whether you have intake (useless on this motor btw) or exhaust mods (useful). One box fits all.

 

On my 2008 bmw 535 wagon I had the Dinan ECU tune done back then and while it was an obvious difference in driving more aggressively, it also improved the fuel economy under gentle throttle on highway trips so it was a big win, also dealer installed so there were no warranty concerns.

For the OCTA 4.4 bmw engine, I'm curious to find more info about this non-ecu JB4:
https://burgertuning.com/products/jb...JSRP6V7zspgh4_

 

I have a used one that I took off of my P400 for sale, If anyone is interested, great little unit.

 

Installed on my 2022 110 SE P400 i6 today. Thus far on Level 4 with noticeable improvement in torque and a more linear throttle response. Easy install other than removing the rear harness (Boost 1) since it was a very tight fit for my large hands. Will have to see the impact on fuel economy etc.

 

@Ford Nice mounting location (I chose the drivers side b/c I have winch wiring / accessory wiring in the passenger area).

After many months, I’ve forgotten I even have this on the car but I like the extra goose it gives. I do really like it.

I did have one trip to Los Angeles in January 2026 where I was getting a stumble or miss at part throttle on the highway. When maintaining steady speed, if I tipped in the throttle partially to accelerate, the car would each time do a single “jerk” (a miss?) This happened 3-4 times on one morning going up a mountain pass. No chk engine lights or codes (I checked the Gaptool, although I didnt check misfires, I couldn’t remember how). I’ve just moved between OR and WA and drove the car back-forth a # of times on the highway under similar condition without issue. I’m chalking it up to bad gas or something else amiss. I don’t think it was the TDI box/ TDI tune but you never know. I was running it on either setting 5 or 6.