BMW Control Systems: DSCs, DTCs and DBCs Dial in ABS, Handling and Traction
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BMW Control Systems: DSCs, DTCs and DBCs Dial in ABS, Handling and Traction

Automotive technology continues to evolve in

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Then, there are some manufacturers, like BMW, that look at all aspects of automotive technology. From the fuel-sipping but sporty MINI, to the 1 ­Series and diesel power, on up to the most luxurious models including SAVs (Sports Activity Vehicles), BMW is bringing the newest technology to the market now, rather than looking years down the road. Vehicle control systems have been on many BMW models since the late 1980s; to say the company has experience with vehicle stability is an understatement.

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BMWs have been one of my favorite manufacturers for years. The cars are well made, practical and there have been models that fill every niche. The available performance has been matched with ­advances in braking and handling that makes these cars some of the best driving cars available from any manufacturer. As BMW’s advertising states, it’s the “Ultimate Driving Experience.”

In the last couple of years, the number of developments in handling, braking and stability systems have been dramatically increasing. Though BMW and Mercedes-Benz are ahead of the industry in providing vehicle stability systems, all of the major manufacturers have installed stability controls on many of their models. The need for auto technicians to stay current and knowledgeable of these technology changes, and the need for continuing education, is more important than ever.

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If you do maintenance or repairs on these cars, you are going to need to learn how every change is connected to the other systems on the car, and how making repairs or simple ­adjustments may mean additional steps. Good diagnosis is going to require the front counterperson to ask the proper questions and the technician having a plan to make sure the diagnosis is complete and correct, based on the description from the customer, the write up from the advisor and having some knowledge of the vehicle maintenance history.

This article cannot begin to teach you everything you need to know about the advanced technology on BMW cars, but, hopefully, will inspire you to seek more information, and refer to the available information that is just a few mouse clicks away. On-line ­repair information is a good, resourceful first step to making successful repairs.

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The problem with any information made available for the aftermarket is the lag time between when the new models come out and when information of any kind is available. That is where having a good working relationship with a local dealer, especially the parts and service department, is so valuable when that new car owner shows up and you don’t want to send him away. As new technology comes to market, car owners are going to bring “problems” to you that turn out to be design changes meant to enhance vehicle control.

More electronic controls make the need for additional test equipment and better diagnostic techniques a priority. In this article, I will present some of the technology that has been introduced on BMW cars over the last few years, where the pattern ­failures have tended to appear, and the best way to go about diagnosing and repairing them, without sending them off to the dealer. Be aware that, in some cases, that may still be needed, particularly where re-programming or recoding is needed. Not all shops are going to be able to invest in the equipment needed to do those final steps that will make the car whole again. Keeping in touch with other local independents, or joining on-line tech forums in conjunction with on-line tech information services, can help you diagnose difficult problems.photo 1

I would also caution you that when we are talking about cars with extremely high-performance capabilities, taking shortcuts on repairs, or trying to get by with lesser quality parts, may be dangerous. Some customers may not like the prices of certain repairs, but the cost of doing a lesser repair could be much higher.

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THE BASICS

As mentioned earlier, having a proper plan in place to make a good diagnosis is going to produce a successful repair. Just as important is exceptional attention to detail when it comes to doing even general maintenance. Using the wrong fluids, not taking the time to clean components completely (see Photo 1) or failing to lubricate them properly could cause other problems that will make additional repairs necessary when control units sense a problem.

The most important system on BMW cars, as well as most other brands, is going to be the brake system (see Photo 2). Because the brakes are used as the “control” for stability, traction control and ABS, the brakes have got to work properly to prevent setting codes in any of the systems. Whenever there is a problem in any of the various stability systems, the brakes should be evaluated before any further diagnosis.

As I have covered in previous articles, everything on these cars is interconnected through the CAN bus wiring (some models are phasing in wireless communication), so a problem in one system can adversely affect one, if not all, other systems. Over time, seemingly unrelated problems can change how the main components work and interact. For this reason alone, it is important to have some knowledge of the vehicle history, particularly major repairs, to have any chance of tracking down a problem with complex vehicle control systems.photo 2

Additionally, you need to have at least a basic ­understanding of how the various control systems work and how they interact. For particularly difficult problems, a look through the owner’s manual can sometimes be a first step in resolving what seems like a more complicated issue.

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I still don’t have much luck working the various versions of the I-drive system, like many car owners. A lot of the various control systems can be “user” ­adjusted, and what seems normal for one driver may throw another driver in the household into paranoia thinking something is going wrong. Just about every one of the newer technologies has an adaption component that makes changes based on typical driver inputs, so your test drive might not be representative of the way the car is usually driven.

With all that said, there are going to be large numbers of these cars coming out of the factory maintenance program that have had little, if any, regular maintenance. It’s usually the second owner who starts encountering the problems left by the original purchaser. That is where it becomes necessary to get involved with driver orientation, particularly if the new purchaser doesn’t have the owner’s manual.

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NEW SYSTEMS

ABS, traction control, variable rate steering and limited slip differentials can all be considered vehicle stability components, but it is when they are connected and work together to control a number of functions that they become an integrated part of vehicle control operation.

On the latest BMW models, these functions have been combined into control systems with new acronyms: DSC (Dynamic Stability Control); DTC (Dynamic Traction Control); and DBC (Dynamic Brake Control). Then, there are components of these systems that control various parts of the driving program, such as Active Steering, Adaptive Transmission Management and the BMW all-wheel-drive system, xDrive.

Since we won’t see these newest cars for a few years, I’ll be focusing on the cars that have been around the block a few times and are just starting to come off lease, or being resold as things start to deteriorate and repairs are imminent. As cars reach 50K without having much more than oil changes (sometimes only two!), there will be some failures or overlooked faults that will be showing up, just as the new owner gets comfortable with his/her new ride.

VEHICLE STABILITY CONTROL  

Some form of stability control has been on certain BMW models since 1987 with the introduction of the traction control system, ASR. In the mid-1990s, Electronic Stability Control was added to some of the high dollar cars and, by the 2001 model year, it was standard on all BMW models. As ABS, ASR, and steering and suspension control have improved, they have been ­integrated into the current Dynamic Stability Control system. Control of just about every system on the car, from the throttle body to HVAC, can be taken away from the driver while the DSC is operating. On some models, DSC cannot be overridden to manual control.

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There may be more or less functions to the stability system, ­depending on the year and model of BMW on which you are working. So, you will need to do a little homework on any vehicle that comes into the shop with faults ­before you begin any diagnosis, so you don’t go off on a wild goose chase, looking for a system that doesn’t apply.

Before diagnosing any fault code, you also need to realize that a fault code often gives you only the component that isn’t working, not the component or components that are the cause of the fault. Because all of the various control systems are connected to the same communication network (CAN), a fault in one may cause a fault code to set in another.

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Pattern failures for DSC codes on most of the models from 2002 to 2007 have mainly been caused by ­either programming or communication errors, which can come from anywhere.  

Always start your diagnosis by eliminating the basics and exploring the vehicle history. Problems with the TPMS systems (either wheel mounted or integrated with the ABS system) can cause codes to be set that will eventually get to the DSC system. Wheel slip caused by weather factors can cause throttle control module movement that could set codes. Body ­repairs, water leaks and even something as strange as having a CD in the player during diagnosis have been reported as causing problems.

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Communication errors have come from pins being pushed out of multi-plugs during repairs, or not connected during body repairs. Since the sensing components are located in various places on different models, any added accessories or upgrades need to be suspect. Steering angle faults have been caused by a number of seemingly harmless repairs, like wheel alignments or component replacements after accidents.

DIAGNOSTIC PLAN

So, how do you deal with a car that comes in with a DSC/DCX indicator light on, but no obvious driveability problems? Here is my suggestion on how to proceed. How you work through the diagnosis is going to depend a lot on how much initial information you have on a particular car.

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1. After getting as much information from the car owner or service writer, you should take a test drive to verify any obvious faults the owner might have missed. Pay attention to braking, steering and any unusual operational quirks.

2. Check for codes if you have the proper software and a compatible scanner.

3. Do a physical inspection of the vehicle, looking especially at the brakes, sensor wiring and evidence of damage or previous repair. Pay close attention to tire condition, size, location on the car (some models have different size wheel/tire specs front and rear) and pressure.

4. Check the condition of the battery. BMW recommends that a battery charger that can supply a consistent voltage be used during any diagnosis that will require ­extended periods with the key in the run position.

5. Assuming there are codes, check available service and repair guides for direction in locating the fault. This is where access to an on-line data service is helpful to indicate whether there are ­applicable TSBs or pattern failures.

6. If TSBs indicate coding or ­reprogramming functions that you don’t have the capability to perform, this is the time to ­attempt a reboot on the car by disconnecting the battery to clear any codes. You should have the customer’s approval for this, as it will erase memory in many of the onboard control units. You should also have all of the keys normally used to start the vehicle available to program, just in case. Unlock the doors, put the windows down, disconnect the battery cables (both) and then connect them together for 20 to 30 minutes.

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7. After reconnecting the battery, if the fault codes return, there may be a need to replace one or more control units if another (sensor) fault cannot be located. The car will most likely need a trip to a dealer to recalibrate or reprogram systems to get full functionality back if you don’t have access to the needed scanner or software.

FINISHING UP

Nothing about auto repair is going to get easier. To maintain an up-to-date knowledge of current and future technological advances, you need to continue to learn. The difference between good and exceptional technicians has always been the desire to understand how things are designed to work so they can be repaired to operate as designed.  

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In the next few years, you will be seeing a lot of these advances on every car from the cheapest to the most expensive, from the grocery getter to the all-out performance car. Active suspension, active steering, electric braking and steering are all technologies that are just now being introduced on the most technologically ­advanced models. We will all need to learn how they work so we can fix them when they break. Murphy’s Law lives on.

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