EDIT: For some weird reason I can't paste Youtube links - but other links work fine. If you can help me fix this, I'll edit the post to get the links working. But just inserting a URL that's a Youtube address doesnt' work.... :-(
My 2004 E46 325i DSC warning light came on over the weekend.
After spending a lot of time reading, I thought I'd put together a sensible list of actions to take if you suffer the same problem - I didn't really manage to find this problem tackled properly in any given place. Hopefully this saves someone going through what I did. So here goes.
What is the DSC system?
First off, before we diagnose a problem with a system, let's start of with what the system actually does.
DSC stands for Dynamic Stability Control. What is this really? It's basically a system (or a computer) which monitors how your car is cornering by looking at the speed at which the wheels are turning, how hard you're pressing the brake and how fast/hard the car is turning and attempts to redistribute the weight evenly by applying the brakes on a wheel by wheel basis. By ensuring even weight distribution, the car can corner much quicker without over or understeer. So it's really a system to enhance performance if you're driving pretty aggressively - during "normal" driving for the vast majority of people, DSC does not do anything.
How does the DSC system work?
There are several versions of this depending on the age of your E46. This link here contains the BMW technical overview of the DSC system: http://forum.e46fanatics.com/attachment.php?attachmentid=483992&d=1356885136 (credit to the poster, and apologies I seem to have lost the link to the thread, so I don't know who they are...)
As you can see from the overview, the DSC system is essentially a computer whose inputs are:
1. All the wheel speed sensors used by the ABS
2. Two brake pressure sensors (front and rear) which enable the DSC to figure out how hard you're trying to break
3. A sensor which enables the DSC system to figure out how hard the car is turning. This is EITHER:
(a) A steering wheel angle sensor (which tells it where the front wheels are pointing, on earlier models, OR
(b) A rotation rate sensor which tells the DSC system how hard the car is accelerating sideways
This already tells you that the DSC system is quite complex with a whole ton on sensors going all over the car. If any of these sensors generates a signal which the DSC computer thinks is anomalous (e.g. loose connection, dirt in sensor, dead sensor) the DSC computer will switch off the system (i.e. it won't attempt to control your brakes) and display the warning light to let you know the system is not working. You can simulate this yourself when the DSC system is working by holding the DSC switch down for 3 seconds.
Implication 1:
Any DSC system related problem could therefore be one of many things. When researching this topic, there are a ton of "experts" on the internet quite happy to dispense advice along the lines of "just top-up the brake fluid / use a higher octane fuel / sacrifice a goat on an even dated Sunday" in order to clear the light. Without looking at the cause of the problem they would be better advised to not provide advice, and you would be advised to treat said advice as someone recommending you to sacrifice a goat on an even dated Sunday - i.e. ignore the crazies.
Implication 2:
The DSC is far from a safety critical system (unless you have an ABS problem - more on that later). All driving with the DSC off is only as dangerous as driving a car without a dynamic stability control system - i.e. not at all IMHO. So don't worry about driving your car without DSC too much (but obviously do so at your own risk!). Now if you're trying to best your Nurburgring lap time, then it's a different story.
Implication 3:
The complexity of the system implies DSC problems are frequently intermittent. There are a ton of places where things can lead to intermittent failure (dirt in sensors, wiring connections). This unfortunately causes people to imply all sorts of causality (e.g. top-up brake fluid) when in fact it's just an intermittent problem.
Implication 4:
Before problem solving, diagnosing the exact cause of the problem is key - otherwise you have no idea if you're spending time/money solving the wrong problem.
So anyways, you've got this far.
How to diagnose the DSC warning light?
First step, there actually three major types of DSC failure:
Type 1: DSC fails but ABS still works (two yellow lights)
You will know you have this because you will have the centre triangle light with the circle around lit AND the yellow brake warning light. But you will NOT, I repeat, NOT have the ABS light on.
This tells you that the ABS is still working, which means the ABS system (and by implication very likely the DSC system) is successfully receiving clean data from all 4 wheel speed sensors. If you have this issue, then you can safely ignore all wheel speed related cleaning / replacement suggestions which abound on the internet. Your problem is more likely to be brake pressure sensor, or steering wheel / rotation rate sensor related
Type 2: DSC fails AND ABS fails (three yellow lights)
This is like Type 1, but you have the ABS yellow light on as well. This means that at least one of the ABS wheel speed sensors is not providing clean data, and as a result both the ABS and the DSC systems have gone off. Here the problem is more safety critical as ABS is a key feature of the car - you should look to solve the issue as a greater priority IMHO
Type 3: DSC fails with no other lights on (one yellow light)
This most probably indicates that brake pressure and wheel speed sensor readings are OK, but there is likely a problem with either the steering position sensor or the yaw rate sensor.
My advice is, irrespective of what type of DSC problem you have, the first step is to read the codes.
How do you read the codes?
I'm a newbie at this, but here is what I learned. Your options here are two fold:
1. Have someone do it for you
At least in London where I live, this is problematic for me - it's (a) expensive, (b) you need to have enough trust in the person reporting the data they've read to you to be able to make expensive decisions based on it - while they're clearly conflicted. But maybe this differs for you - anyways, get them to read the codes which should pin point exactly the problem you're having.
2. Do it yourself
You can buy cheap scanners these days (it's what I'm doing). It's important to note that the cheapest generic type of scanner you can get on eBay for next to nothing WILL NOT enable you to diagnose DSC problems as these are BMW specific. So if you're doing the diagnosis yourself, you need to buy a cable which plugs into a PC laptop and use the INPA software on the laptop. Note that your car stores the warnings which have occurred - so even if your light is not on when you get your hands on the scanner, you can still see what caused the problem.
That said, getting INPA up and running and scanning the car is definitely a task for the patient - the SW was written sometime in 1982 and getting it up and running on the modern PC is a challenge. If you do persevere, make sure you turn the ignition on when trying to connect to the DSC - it seems to be the only component of the car which needs the ignition on!
I've read the codes, now what?
Hopefully now you have some idea of what the problem is. Towards a solution:
1. If you have a Type 1 DSC problem above, and the codes point to a brake pressure sensor, then the easiest thing to try unplugging and replugging the DSC connector back in. Actually, given how simple this is, there's no reason not to try this under all circumstances - it will save on sacrificing a goat anyways. See this
http://www.youtube.com/watch?v=De5mY0cObyg
The guy says it cleared the problem for him for 2 years. I had a code 5E21 (break pressure sensor) and did the unplug and replug and so far it's worked for me. I'm not for a second suggesting it will work for you, but easy enough to try.
Obviously if you really do have a pressure sensor problem and this doesn't clear it, then you need to replace the brake pressure sensor. There isn't really a howto on than that I've found, but this guy seems to help:
https://autotecdirect.com/2012/04/25/bmw-e46-dsc-pressure-sensor-replacement/
This guy replaces the brake booster without bleeding the system. You should be able to figure out how to do the sensors as well from this, although not explicit
See video here
2. If you have a Type 2 DSC problem, then you need to look at your wheel sensors.
Here's a good howto on how to clean / replace them:
http://www.youtube.com/watch?v=T4-bopzGaUE
3. Any other problem - well, I'm afraid you're on your own....
Anyways, thanks for reading and good luck getting this fixed if you've got this far.
PS For some reason I can't post Youtube clicky links - apologies.
My 2004 E46 325i DSC warning light came on over the weekend.
After spending a lot of time reading, I thought I'd put together a sensible list of actions to take if you suffer the same problem - I didn't really manage to find this problem tackled properly in any given place. Hopefully this saves someone going through what I did. So here goes.
What is the DSC system?
First off, before we diagnose a problem with a system, let's start of with what the system actually does.
DSC stands for Dynamic Stability Control. What is this really? It's basically a system (or a computer) which monitors how your car is cornering by looking at the speed at which the wheels are turning, how hard you're pressing the brake and how fast/hard the car is turning and attempts to redistribute the weight evenly by applying the brakes on a wheel by wheel basis. By ensuring even weight distribution, the car can corner much quicker without over or understeer. So it's really a system to enhance performance if you're driving pretty aggressively - during "normal" driving for the vast majority of people, DSC does not do anything.
How does the DSC system work?
There are several versions of this depending on the age of your E46. This link here contains the BMW technical overview of the DSC system: http://forum.e46fanatics.com/attachment.php?attachmentid=483992&d=1356885136 (credit to the poster, and apologies I seem to have lost the link to the thread, so I don't know who they are...)
As you can see from the overview, the DSC system is essentially a computer whose inputs are:
1. All the wheel speed sensors used by the ABS
2. Two brake pressure sensors (front and rear) which enable the DSC to figure out how hard you're trying to break
3. A sensor which enables the DSC system to figure out how hard the car is turning. This is EITHER:
(a) A steering wheel angle sensor (which tells it where the front wheels are pointing, on earlier models, OR
(b) A rotation rate sensor which tells the DSC system how hard the car is accelerating sideways
This already tells you that the DSC system is quite complex with a whole ton on sensors going all over the car. If any of these sensors generates a signal which the DSC computer thinks is anomalous (e.g. loose connection, dirt in sensor, dead sensor) the DSC computer will switch off the system (i.e. it won't attempt to control your brakes) and display the warning light to let you know the system is not working. You can simulate this yourself when the DSC system is working by holding the DSC switch down for 3 seconds.
Implication 1:
Any DSC system related problem could therefore be one of many things. When researching this topic, there are a ton of "experts" on the internet quite happy to dispense advice along the lines of "just top-up the brake fluid / use a higher octane fuel / sacrifice a goat on an even dated Sunday" in order to clear the light. Without looking at the cause of the problem they would be better advised to not provide advice, and you would be advised to treat said advice as someone recommending you to sacrifice a goat on an even dated Sunday - i.e. ignore the crazies.
Implication 2:
The DSC is far from a safety critical system (unless you have an ABS problem - more on that later). All driving with the DSC off is only as dangerous as driving a car without a dynamic stability control system - i.e. not at all IMHO. So don't worry about driving your car without DSC too much (but obviously do so at your own risk!). Now if you're trying to best your Nurburgring lap time, then it's a different story.
Implication 3:
The complexity of the system implies DSC problems are frequently intermittent. There are a ton of places where things can lead to intermittent failure (dirt in sensors, wiring connections). This unfortunately causes people to imply all sorts of causality (e.g. top-up brake fluid) when in fact it's just an intermittent problem.
Implication 4:
Before problem solving, diagnosing the exact cause of the problem is key - otherwise you have no idea if you're spending time/money solving the wrong problem.
So anyways, you've got this far.
How to diagnose the DSC warning light?
First step, there actually three major types of DSC failure:
Type 1: DSC fails but ABS still works (two yellow lights)
You will know you have this because you will have the centre triangle light with the circle around lit AND the yellow brake warning light. But you will NOT, I repeat, NOT have the ABS light on.
This tells you that the ABS is still working, which means the ABS system (and by implication very likely the DSC system) is successfully receiving clean data from all 4 wheel speed sensors. If you have this issue, then you can safely ignore all wheel speed related cleaning / replacement suggestions which abound on the internet. Your problem is more likely to be brake pressure sensor, or steering wheel / rotation rate sensor related
Type 2: DSC fails AND ABS fails (three yellow lights)
This is like Type 1, but you have the ABS yellow light on as well. This means that at least one of the ABS wheel speed sensors is not providing clean data, and as a result both the ABS and the DSC systems have gone off. Here the problem is more safety critical as ABS is a key feature of the car - you should look to solve the issue as a greater priority IMHO
Type 3: DSC fails with no other lights on (one yellow light)
This most probably indicates that brake pressure and wheel speed sensor readings are OK, but there is likely a problem with either the steering position sensor or the yaw rate sensor.
My advice is, irrespective of what type of DSC problem you have, the first step is to read the codes.
How do you read the codes?
I'm a newbie at this, but here is what I learned. Your options here are two fold:
1. Have someone do it for you
At least in London where I live, this is problematic for me - it's (a) expensive, (b) you need to have enough trust in the person reporting the data they've read to you to be able to make expensive decisions based on it - while they're clearly conflicted. But maybe this differs for you - anyways, get them to read the codes which should pin point exactly the problem you're having.
2. Do it yourself
You can buy cheap scanners these days (it's what I'm doing). It's important to note that the cheapest generic type of scanner you can get on eBay for next to nothing WILL NOT enable you to diagnose DSC problems as these are BMW specific. So if you're doing the diagnosis yourself, you need to buy a cable which plugs into a PC laptop and use the INPA software on the laptop. Note that your car stores the warnings which have occurred - so even if your light is not on when you get your hands on the scanner, you can still see what caused the problem.
That said, getting INPA up and running and scanning the car is definitely a task for the patient - the SW was written sometime in 1982 and getting it up and running on the modern PC is a challenge. If you do persevere, make sure you turn the ignition on when trying to connect to the DSC - it seems to be the only component of the car which needs the ignition on!
I've read the codes, now what?
Hopefully now you have some idea of what the problem is. Towards a solution:
1. If you have a Type 1 DSC problem above, and the codes point to a brake pressure sensor, then the easiest thing to try unplugging and replugging the DSC connector back in. Actually, given how simple this is, there's no reason not to try this under all circumstances - it will save on sacrificing a goat anyways. See this
http://www.youtube.com/watch?v=De5mY0cObyg
The guy says it cleared the problem for him for 2 years. I had a code 5E21 (break pressure sensor) and did the unplug and replug and so far it's worked for me. I'm not for a second suggesting it will work for you, but easy enough to try.
Obviously if you really do have a pressure sensor problem and this doesn't clear it, then you need to replace the brake pressure sensor. There isn't really a howto on than that I've found, but this guy seems to help:
https://autotecdirect.com/2012/04/25/bmw-e46-dsc-pressure-sensor-replacement/
This guy replaces the brake booster without bleeding the system. You should be able to figure out how to do the sensors as well from this, although not explicit
See video here
2. If you have a Type 2 DSC problem, then you need to look at your wheel sensors.
Here's a good howto on how to clean / replace them:
http://www.youtube.com/watch?v=T4-bopzGaUE
3. Any other problem - well, I'm afraid you're on your own....
Anyways, thanks for reading and good luck getting this fixed if you've got this far.
PS For some reason I can't post Youtube clicky links - apologies.
