Bmw Smg Transmission

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Few things fill car enthusiasts with impotent rage quite like BMW’s sequential manual gearbox (SMG). That’s especially true when it’s bolted to the excellent, raspy-sounding S54 in the beloved E46 M3.

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I’ll be the first to tell you that I’m a manual elitist. Only a small percentage of the dozens of cars I’ve owned have been automatics, and I’m currently undergoing the laborious and expensive process of swapping my E34 Touring over to a three-pedal configuration.

I understand that modern automatics are faster, but I don’t care. Driving a manual is just more fun. It’s more involved, more engaging, and offers an additional layer of control when driving.

Bmw Smg Transmission Reliability

That said, I have driven cars with some very good automatic transmissions. However, the SMG is neither.

The SMG II found in the E46 M3 is based heavily on the Getrag six-speed found in three-pedal versions of the car. When these cars were new, their buyers, many of whom were still riding high on the money they made during the dot-com boom, opted for the latest, fanciest tech for their new sports car. As a result, it seems like SMG E46 M3s are easier to find than their six-speed siblings.

This may just be my experience, but it seems like a lot of folks who dislike the SMG have never had the opportunity to drive one. In fact, few who have driven one have had the opportunity to drive one properly.

While the SMG does feature an automatic mode, using it is a disservice not only to you, the driver, but to the car itself. These cars love to be flogged, and they repay that abuse in spades.

My good friend Bill owns—and daily drives—an SMG-equipped E46 M3. Nothing short of road salt and freezing temperatures (which tend to turn sticky summer tires into hockey pucks) keep it in the garage.

Bill has owned the car for several years. Incredibly, he sold an air-cooled Porsche 911—purchased well before the infamous boom in prices for such cars—to fund the purchase. To this day, he has no regrets. After spending some time in his car, I can understand why.

Over the years, Bill has upgraded and personalized his M3 to suit his needs as a weekend warrior track toy and a weekday commuter. He’s slowly transformed his car into a near-perfect replica of his dream car, an E46 M3 CSL, forbidden fruit for us Americans. The processes has included replacing the entire roof with a carbon fiber panel.

Bmw Smg Transmission

Bmw Smg Transmission Fluid

Thankfully, Bill’s commute consists almost exclusively of winding, undulating two-lane county highways—backroads in the truest sense of the term.

Every day offers another opportunity to hone the same skills he uses when he attacks Mid-Ohio and Gingerman with all his might. Apparently, the SMG has learned from this behavior, and it has learned well.

Bill likes to point out that the E46 M3 CSL, for all of its intensive weight-saving measures and race car posturing, utilized an SMG. There’s a good reason for it, too.

The first time I went to lunch with Bill, I strapped myself into the fixed racing seat and prepared for what should have been a routine trip to Chipotle. Instead, I got a thrill ride.

I’d be lying if I had said that I hadn’t initially wondered why he opted for the “inferior” transmission. That question was answered when he launched the car in S6 from the very first stoplight. Once I had regained my breath, I scraped my eyeballs from the inside of the rear window. I was speechless.

This sucker was fast. Each lightning-quick shift came with an immediacy and brutality not unlike a Viking raid. I had never experienced anything like it from any manual transmission car I had ever driven.

Bmw smg transmission review

I still prefer manual transmission cars, and I always will. But someday, when I shop for an E46 M3 of my own, there’s a very good chance that I will make the same choice Bill did. If you think that’s wrong of me, I can’t wait for the opportunity to show you how I came to that conclusion.

When that day comes, I hope I do Bill proud. Hold onto your eyeballs.—Cam VanDerHorst

[Photos via William Jackson, ECS Tuning.]


In 1996, BMW M introduced a manual transmission that was capable of shifting gears automatically without the use of a conventional clutch pedal or mechanical shifter lever. The system was called the SMG I. Derived from Formula 1 racing technology; SMG stands for Sequential Manual Gearbox.

The U.S. received the first SMG in the 2001 E46 M3. This system was referred to as SMG 2. The 6-speed manual gearbox manufactured by Getrag, operated in automated “A” mode and performed similar to an automatic transmission or in sequential “S” mode, which allows the operator to shift manually through the gears.

In sequential mode, the driver shifts up and down through the gears by simply operating the shifter lever or a pair of paddle shifters mounted on either side of the steering wheel. Individual gear selection is realized by electrical/hydraulic actuation of both, the gearbox selector forks and the (conventional) clutch assembly.

System Components

The SMG II system is consists of the following components:

  • Basic Gearbox (S6S420G, Getrag type D)
  • SMG II Control Unit (Siemens)
  • SMG CAN Bus
  • DME Control Unit (MSS54)
  • Hydraulic unit and solenoids
  • Gearbox Actuator
  • Clutch Slave Cylinder with PLCD (Permanent Linear Contactless displacement)
  • Shift Lever Module with Shift Lock
  • Steering Wheel Paddle mounted switches
  • DRIVELOGIC Control
  • Display in instrument cluster
  • DSC control unit
  • SAC dry single disc clutch

SMG II Control Unit

The SMG II Control Unit, installed in the E-Box next to the DME, is a single board module with SKE (134 pin) gray colored connectors. The unit contains protection against reverse polarity and overvoltage.

Communication with the DME is via a dedicated CAN bus (SMG II CAN Bus). Based on instructions received from the DME the SMG II control unit manages the clutch solenoid valve, the selector shaft up and down solenoids, and the selection angle solenoid. Safety functions and limp home capabilities are also part of the SMG II programming.

While the SMG II control unit receives many of the inputs and manages the control of the hydraulic system, the DME is responsible for and controls all gearshifts. Sensor inputs received by the SMG II control unit are relayed to the DME for processing and monitoring.


The SMG CAN Bus is the link for signal exchange between the DME and SMG II Control Unit. It allows the DME to issue command instructions for clutch and gearbox control as well as shift sequence and enables SMG II communication with the vehicle CAN BUS via the DME.

Bmw Smg Transmission

Signals exchanged via SMG CAN Bus:
Engine Speed, Engine Coolant Temp, Engine Oil Temp, Intake Air Temp, PWG, EDR Feedback Pots, Wheel Speed, Transverse Acceleration, Steering Angle, Cruise Status, Parking Brake, Door Contacts, Brake Light Switch, Key Memory

SMG II Diagnosis

The SMG II control unit is fully diagnosable and can be checked using ISTA/D. The first step involves the fault memory being read out. Malfunctions are communicated as part of the SMG II control unit’s self-diagnosis. The second step involves appropriate operator prompting to facilitate diagnosis with simple measuring equipment using test modules.
Repairs can be made once the fault in question has been found.
The diagnosis including self-diagnosis can only be carried out when the ignition (terminal 15) is switched on and there is a supply voltage of at least 10 volts. Erroneous fault entries may be recorded if the supply voltage drops below the threshold of approx. 10 volts.

Service Functions

A test program (service functions) must be carried out upon completion of various types of work on the SMG system – see the following table. The test programs serve to implement test, initialize and adjustment functions.
The values determined are permanently stored in the non-volatile memory only after the test program has been success-fully completed.


Bmw Smg Transmission Fluid

Checking & topping up fluid level in hydraulic system (S6S 420G SMG)

  • Turn on ignition
  • Press brake pedal
  • Move selector lever from position “0” to “R” or “0” to “E” until hydraulic pump is activated
  • Wait until hydraulic pump shuts down
  • Open expansion tank (1)
  • Fill expansion tank up to MAX marking (2) on dipstick (1)

Smg Transmission Problems

NOTE: Check when cold. Check with dipstick on cap; for this, screw in cap.