The S tronic Gearbox Bible

This post covers everything you need to know about the Audi S tronic dual clutch gearbox fitted to the B8 and B8.5 S5, from how it works, to how much power (torque) it can handle, tuning options, common problems and faults and when it needs servicing.

Audi S tronic 7 speed gearbox transmission cutaway engineering diagram This post may contain affiliate links. Please read my disclosure for more info.


Contents

I'd recommend reading through the whole article, but if you're in a hurry you can skip to a specific section of this article using the links below.

Audi S tronic vs DSG vs multitronic vs Tiptronic?
How Does the Audi S tronic Gearbox Work?
S tronic Gearbox Variants
S tronic Service Schedule
Modifying a Car with an S tronic Gearbox
S tronic Remap (TCU Upgrade)
Audi 7 Speed S tronic Problems and Reliability
Symptoms and Fault Codes
Audi S tronic Mechatronic Unit Repair Options and Costs
Audi S tronic Dual Clutch Repair Options and Costs


Why Write About the S tronic Gearbox?

The thought hadn't even crossed my mind to write a post about the Audi S tronic gearbox, that was until I discovered how little I knew about it. Shameful really having owned my S5 well over a year now...

Whilst researching the S tronic service / maintenance schedule, I stumbled across the cutaway engineering drawing of the S tronic transmission below and was fascinated by just how complex it appeared, and naturally wanted to learn more.

Many hours of reading later I started composing this post. I know it's a bit of a diversion from my usual content but stick with it because I hope you'll find it as interesting to read as I found writing it (you're bound to if you're an engineering nerd like me).



Audi S tronic vs DSG vs multitronic vs Tiptronic?

The first thing to nail down is, what does S tronic mean? The answer is... not a lot, it's just Audi's name for their latest DSG (Direct-Shift Gearbox) offering. S tronic and DSG can be used interchangeably if you so wish, however, S tronic is definitely not the same as multitronic or Tiptronic.

In short, S tronic is a dual clutch DSG and has a number of variants, both longitudinal (as fitted to the S5) and transverse, and 6 or 7 speed.

multitronic is a continuously variable transmission (CVT), it works by running a tension chain between two pairs of variable conical pulleys. Moving the pulleys further apart or closer together changes the gear ratio. For a full description visit the Multitronic Audi Technology Portal page.

Tiptronic is a more traditional automatic gearbox featuring a torque converter, as appose to the dual clutch of the S tronic transmission. For a full description visit the Tiptronic Audi Technology Portal page.


How Does the Audi S tronic Gearbox Work?

Elaborating on my brief description earlier in the post, here's Audi's full description:

Audi S tronic gearbox operating principle diagram
"The S tronic [gearbox] comprises two subunits and integrates two multi-plate clutches that control the various gears. The large K1 clutch located on the outside directs the torque via a solid shaft to the gear wheels for the odd-numbered gears 1, 3, 5 and 7. A hollow shaft rotates around the solid shaft. It is connected to the smaller K2 clutch, which is integrated into the inside of its larger sibling, and which controls the gear wheels for the even-numbered gears 2, 4 and 6, as well as the reverse gear."


"Both transmission structures are continuously active, but only one is connected to the engine at any one time. For example, when the driver accelerates in third gear, the fourth gear is already engaged in the second transmission structure. The shifting process takes place as the clutch changes – K1 opens and K2 closes."

This means that the S tronic gearbox can shift gears in under 0.2 seconds offering almost seamless power delivery, pretty damn impressive!

I'm a big fan of the Engineering Explained YouTube channel, so any excuse to promote Jason's videos and I'm on it. In this video he explains how a VW Passat transverse DSG works.


For an even more in-depth look at the 0B5 gearbox, Google "Audi Self-Study Programme 429" or "SSP 429" and skip to page 22.



S tronic Gearbox Variants

There are a number of variants of the S tronic transmission, the original being the transaxle DQ250 (part number prefix: 02E).

In 2008 Audi developed the longitudinal S tronic gearbox found in the B8 and B8.5 S4 / S5, code named DL501 (part number prefix: 0B5). It weighs 142kg including the dual mass flywheel and oil. There are multiple generations of the DL501, Gen 1, Gen 1.5 and Gen 2.


S tronic Service Schedule

If maintained, the S tronic gearbox is usually pretty reliable. Quoting Audi UK, "To ensure the continuous smooth running of your [S tronic] transmission it is essential that the oil is changed no later than every 38,000 miles [61,155 km]."

Audi service workshop area
In the UK, Audi offers an S tronic transmission oil and filter change for a fixed price of £225 (2020 price), not outrageous which suggests it's not too difficult or time consuming should you wish to DIY.

Update: Oct 2019

My S5 Sportback is now well overdue the S tronic transmission oil service, I know, I know, I have brought great shame upon my family...


Anyway, I've purposely been holding off, partly because life has gotten in the way but more worryingly, because I'm getting the dreaded "Gearbox malfunction: you can continue driving" warning.

I've been doing even more Googling, forum reading and youtubing to nail down exactly what I need to replace. I will of course be doing a full update of this article with what I've learnt.


Parts Required

If you purely wish to replace exactly what Audi would, during their £225 service, you'd need the following parts:

  • N 013 827 5 - Sump drain plug washer x1
  • 0B5 325 330 A - Exchangeable external ATF filter x1
  • WHT 005 499 A - O-ring for external ATF filter x1
  • WHT 003 487 - New replacement sump drain plug x1
  • G 052 529 A2 - ATF gearbox oil 7L

You should see this option as the bare minimum. If you're going to the trouble of doing the service yourself, you might as well go all in and replace the internal filter as well, not only does this allow you to drain more of the old oil, it allows you to check the magnets in the sump pan for any debris. If you want to replace the internal filter, you'll need the following parts in addition to those above:

  • N 911 511 01 - Cross Member Bolts x6
  • N 910 968 01 - Oil pan bolts x15
  • 0B5 321 371 E - Oil pan gasket x1
  • 0B5 325 429 E - Internal filter / strainer with O-rings x1

I'll be going one stage further, and carrying out a DIY mechatronic unit repair, so for that I've ordered the following:

  • WHT 005 379 - Oil seal between external filter housing and gearbox x1
  • 0B5 321 473 - ATF pipes inc seals between external filter housing & gearbox x2
  • N 906 660 03 - O-ring for metal pipes going into external filter housing x2
  • N 104 057 02 - Mechatronic unit mounting bolts x6
  • 0B5 315 105 TC - Mechatronic clutch pressure pipes x1
  • 0B5 315 105 TA - Mechatronic internal ATF pipes x1
  • 0B5 398 009 F - Mechatronic PCB repair kit x1

The RRP of all these parts is £643.98, I was able to get them for £592 delivered. All will be explained if it works out ok, I want to make sure everything comes good before recommending it to you guys.


Tools Required

In terms of any special tools required, you'll need the following:
  • VCDS or OBDEleven (or similar) to read the live transmission oil temperature
  • Low Range Torque Wrench with 3Nm setting - For Mechatronic Repair Only

I'll be writing my own DIY guide on how to service your 7 Speed S Tronic DSG transmission and DIY mechatronic unit repair but for now, check out this excellent video below from Deutsche Auto Parts.




Modifying a Car With an S tronic Gearbox

The longitudinal 7 speed S tronic gearbox can handle torque figures of up to 550Nm at 9,000rpm according to the Audi Self-Study Programme 429 (SSP 429).

As standard the 3.0 TFSI supercharged V6 in the S5 puts out 440Nm of torque, well within the S tronic's capabilities.

Thanks to the huge tuning potential of the 3.0 TFSI you can end up getting much closer to that 550Nm limit quite easily.

TMC Motorsport chip tuning box

You should be safe with just Stage I modifications though, in my post on choosing the best Audi S5 V6 chip tuning box, all of the tuning boxes claimed to add in the region of 50-75Nm of torque, so topping out at 515Nm. Closer to the 550Nm, but still safe.

APR Stage 1 ECU Upgrade vs Stock graph Audi 3.0 TFSI S4 S5
If you go one further and opt for the APR Stage II ECU and supercharger pulley kit on 98 RON you'll be pushing 535Nm, on 108 RON race fuel you'll be on the limit at 554Nm.

APR Stage 2 II ECU Upgrade and APR Pulley vs Stock graph Audi 3.0 TFSI S4 S5
Although Audi cite 550Nm as the maximum torque, I did find one post on a5oc saying MTM had confirmed the S tronic gearbox can handle 600Nm+, and a company from the Netherlands called TVS Engineering quoting as much as 1000Nm (with their software).

I got in touch with Audi's technical team who confirmed:

"The torque capacity of this [the S tronic] transmission is up to 550 Nm at 9000 rpm."





S tronic Remap (TCU Upgrade)

There are a number of companies offering a remap, or transmission control unit (TCU) upgrade, for the S tronic transmission. I've listed a few of the more popular ones below.

As I found out when researching chip tuning boxes, the price can vary wildly. Each company has their own USP, but most offer the following benefits from their remaps.
  • Reduced gear change time (TMC claim a 28% improvement)
  • Launch Control enabled
  • Increased max Launch Control RPM (APR offering up to 6,000 RPM)
  • Torque limit increased
  • Full manual mode (no automatic change at max or min RPM)
  • Automatic shift RPMs modified

The graph below from APR shows acceleration vs vehicle speed, demonstrating the APR TCU maintaining a higher G throughout the gear range.

APR DL501 vs Stock TCU S tronic remap graph 3.0 TFSI S4 S5


Audi 7 Speed S tronic Problems and Reliability

As technically brilliant as the S tronic gearbox is, it does have it's problems, very costly ones at that. Probably the most high profile case of S tronic gearbox problems is that of Top Gear's Chris Harris on his S4 estate, back in 2014.

Chris Harris S4
You can read the full article on PistonHeads, but basically it ended up costing him £4,129 inc VAT for a full gearbox replacement (an extremely good price, considering a new gearbox would cost the 'general public' £12k+).

Chris Harris gearbox S4 replacement
From what I've read, the two main culprits for 7 speed S tronic problems (or failure) are the dual clutch and the Mechatronics unit.


Symptoms and Fault Codes

Symptoms of a faulty or failed S tronic Mechatronic unit can be poor gear selection or no gear selection at all. If there is damage or fault with the dual clutch, you might experience jolting gear changes, loss of torque moving off in reverse gear and loss of power. The Mechatronics unit appears to be the most common source of problems for the S tronic transmission. Quoting SSP 429: "The mechatronic system controls, regulates and performs the following functions:

  • Adaptation of oil pressure in the hydraulic system to requirements
  • Dual clutch regulation
  • Clutch cooling regulation
  • Shift point selection
  • Gearbox control and regulation
  • Communication with other control units
  • Limp-home programs
  • Self-diagnostics"


Note: Inconsistent or harsh gear changes can be caused by a MAP sensor failure, check out my complete guide to replacing your MAP sensor for more info!

According to the Audi Technical Service Bulletin SB-10054213-2278 if you get the following message appear in the information display:

“Gearbox malfunction: you can continue driving”

Audi Gearbox malfunction: you can continue driving warning message and light
The following fault codes may have been recorded and could point to a faulty Mechatronic unit.

  • DTC P17D8 (Torque limitation because of clutch temperature) with symptom code 8040
  • DTC P0726 (RPM signal of engine control unit, implausible signal) with symptom code 7980
  • DTC P174B (Valve 4 in the sub-gearbox 1, electric fault) with symptom code 8027
  • DTC P174F (Valve 4 in the sub-gearbox 2, electric fault) with symptom code 8028
  • DTC P179C (Main pressure valve, electric fault) with symptom code 8029
  • DTC P179D (Coolant oil valve electrical fault) with symptom code 8030
  • DTC P174C (Partial transmission 1 valve 2 Electrical error ) with symptom code 8026
  • DTC P174A (Valve 3 in the sub-gearbox 1, electric fault) with symptom code 8939
  • DTC P174E (Valve 3 in the sub-gearbox 2, electric fault) with symptom code 8940
  • DTC P1740 (Clutch temperature monitoring) with symptom code 8031


As well as the above error message, there are two others you may experience:

"Gearbox fault: You can continue driving to a limited extent only"

Audi Gearbox fault: You can continue driving to a limited extent only warning message and light
If the above message shows, protective functions are activated to minimise or prevent damage occurring, but result in a loss of performance. Only the gears on the hollow shaft can be engaged (even-numbered gears 2, 4, 6 and R).

"Gearbox fault: You can continue driving to a limited extent only No reverse gear"

Audi Gearbox fault: You can continue driving to a limited extent only No reverse gear warning message and light
If the above message shows, protective functions are activated to minimise or prevent damage occurring, but result in a loss of performance and with no ability to select Reverse gear. Only the gears on the solid shaft can be engaged (odd-numbered gears 1, 3, 5 and 7).



Audi S tronic Mechatronic Unit Repair Options and Costs


The cheapest way to repair your Mechatronic unit is to do it yourself following my DIY Mechatronic unit repair guide.

However, if you'd rather not mess around with swapping circuit boards, but don't mind removing / refitting the Mechatronic unit and doing the S tronic service, you have these two options:


*All prices correct as of 26/11/2020. I've not used any of the above companies, nor am I sponsored or paid to endorse them. Please only part with your hard earned money when you are happy the company will provide the service you expect.

Be mindful the prices above don't include all the parts required to do the S tronic service nor the replacement parts you'll need as a result of removing the Mechatronic unit (seals, ATF fluid, filters etc).

You'll likely need to add at least £350-£400 on top of those prices.

If you want the whole job doing for you, you're looking at £2300+ (based on a figure taken from AC's quote on rmsmotoring)


Audi S tronic Dual Clutch Repair Options and Costs

Audi UK offers a fixed price quattro clutch service, which for my S5 is quoted as £1799 (ouch). Unfortunately Audi doesn't give any details as to what work is carried out for that sizeable sum of cash.

I did contact Audi for more info, but they replied with the following:

"Your local Audi Centre will be happy to confirm what work will be undertaken at the fixed price clutch series"


If you work for Audi, or have had this repair done to your car I'd love to hear your experiences, let me know in the comments below!


Conclusion

That concludes the article for now, as I learn more I'll keep it continually updated. I really hope you enjoyed this post despite being away from the norm, if you did and would like to see more articles like this, let me know in the comments below. Can you add anything to make the guide even more complete? Have you been stung by having to repair or replace your S tronic gearbox and are there any pointers or lessons learned you can share in the comments? Be sure to Like, Subscribe and Follow me on any or all of the usual social media platforms at the following links: FacebookInstagram and YouTube, search andybuck123.

Stay tuned for plenty more content to come!