BMW's Condition Based Service (CBS) system monitors various maintenance items, and alerts you when service is needed. It is found on 2002 and newer 7 Series (E65 & E66), 2004 and up 1 Series (E87), 2004 and up 5 Series (E60 & E61) and 6 Series (E63 & E64), and 2006 and up 3 Series (E90 & E91).
The CBS system monitors the service life of the engine oil and cabin air filter, wear on the front and rear brake pads, and the condition of the brake fluid and spark plugs. On diesel applications, it also tracks the usage and life of the diesel particulate filter. The oil monitoring system, in particular, is quite different from other vehicles in that the engine has no dipstick! There have been some problems with the oil monitor.
The CBS system monitors the service life of the engine oil and cabin air filter, wear on the front and rear brake pads, and the condition of the brake fluid and spark plugs. On diesel applications, it also tracks the usage and life of the diesel particulate filter.
Engine oil is monitored by the DME/DDE engine control module. Oil change intervals are recommended based on fuel consumption and oil quality.
Cabin air filter is monitored by the IHKA climate control module, and is estimated to be 32,000 miles. But the service life is modified based on inputs from the rain sensor, ambient air temperature sensor, fan speed, air circulation, driving speed, heater usage, and time and distance since the last oil change.
Brake fluid life is time based, with a reminder to change the fluid every 24 months.
Spark plug life is mileage based, with a reminder to change the plugs at 100,000 miles.
Front and rear brake pad wear is monitored by the DSC stability control module via brake wear sensors and calculations are based on miles driven, vehicle speed and brake usage.
Diesel particulates are monitored by the DME/DDE engine control module, and are based on mileage.
The system also monitors the service life of the automatic transmission fluid and oxygen sensors, but does not show the data on the instrument cluster or driver display panel. It can be accessed with a scan tool or from a KeyReader (which we will explain shortly).
BMW's service recommendations for the transmission fluid is 100,000 miles, and 120,000 miles for the oxygen sensors.
As for the coolant, the CBS system does not make a service recommendation because BMW says its coolant is a "lifetime" fluid. Yeah, right. Anyway, the condition of the coolant is not monitored and there is no recommended service interval from BMW. Even so, most other vehicle manufacturers recommend a coolant change at five years or 150,000 miles. A coolant change should also be done if the cooling system shows any corrosion, or if you are replacing a radiator, heater core, water pump, thermostat or hoses.
The CBS system can also generate service alerts (which are dealer programmable) for general inspections, emissions inspections or other vehicle checks based on time and mileage.
The CBS system notifies the driver when service is needed approximately four weeks ahead of when it is actually due so the vehicle owner can have time to schedule a service appointment with their local BMW dealer. It is the electronic equivalent of having a service advisor along for the ride.
Monitored items are also color-coded. Where indicator lights are used, green means okay, yellow indicates service is due (which occurs when there is 20% remaining service life) and red means service is past due. On cars where icons are used, orange indicates normal service, yellow means service is due and red means service is overdue.
On some models, the service information is displayed on the instrument panel. On others, you can access and display the information using the "I-Drive" touch control knob on the center console. Move the pointer on the screen down to find the "Settings" menu, and then turn the control knob until "Service" is highlighted. Then press the knob to activate the CBS menu. The menu will now list all of the monitored items and indicate if anything requires service.
Note: This is not the same thing as the OBD II monitors that keep tabs on engine sensors and other emissions-related systems. Problems here can set fault codes and turn on the service light, but will not affect the CBS service monitors.
Here is another feature of the CBS system that is available on some models: it can store and transmit service data to the car's keyless entry fob.
The control unit for the central locking system and immobilizer requests maintenance-related data from the information display. The data is then transmitted through the keyless entry system to the key fob. A BMW dealer tech can scan the key fob with his KeyReader to extract the maintenance information and sell the customer any maintenance that might be needed.
This is certainly handy for a BMW dealer. But what about independent repair shops? I searched the internet and found numerous listings for KeyReader devices (mostly Chinese-made) that can read and display information from a BMW key on a computer. Prices for what appear to be the same unit range from $700 up to $2,200! That kind of money would probably be better spent toward buying a nice European scan tool or some professional-level scanner software for a laptop or PC. On the other hand, if you have a lot of late-model BMW customers, a KeyReader device might help you sell more maintenance service.
Some vehicle manufacturers estimate oil by using mathematical algorithms. The oil monitor keeps track of hours of engine operation, temperature, distance traveled and so on to estimate how much oil life is left. When a certain point is reached, the oil service reminder light comes on.
BMW uses an "adaptive" strategy to compute estimated oil life based on how much fuel the vehicle has consumed (which BMW says is more accurate than tracking the number of miles driven and hours of engine operation). The CBS system also considers input from an oil quality sensor in the bottom of the oil pan. The oil quality sensor measures the electrical conductivity of the oil. As the additives in the oil wear out, the resistance of the fluid changes.
The maximum service interval on late-model BMWs with this system is 25,000 km (15,500 miles, which the driver information display rounds up to read 16,000 miles). As the CBS system tracks fuel usage, it deducts mileage in 1,000-mile chunks from the remaining oil life. When there is an estimated 1,250 miles of oil life left, or if the oil quality sensor indicates a change is due sooner, the service reminder light comes on, and the oil status indicator changes color from green to yellow. Keep in mind that the 15,500-mile oil change interval is based on using BMW's High Performance 5W-30 synthetic oil, not ordinary oil. Also, most of these engines hold 7, 8 or 9 quarts of oil, depending on their crankcase capacity.
It is not clear whether BMW takes into consideration wear factors that accumulate with normal driving. A 15,500-mile oil change interval may be okay for a low-mileage engine with no piston ring or cylinder wear, but what about an engine with 100,000 or 150,000 miles on the odometer? Such long oil change intervals with a high-mileage engine that has more blowby and wear than a new engine may be asking for trouble.
On older BMWs (up to model year 2000), a special tool can be used to reset the oil service reminder light. These tools typically sell for $100 to $150, and plug into a round 20-pin diagnostic connector in the engine compartment. Just remove the connector cover, attach the tool, then flip a switch or press a button to reset the service reminder. Some of these tools can also read and clear powertrain codes.
Another point worth noting on the CBS applications is that you cannot reset the oil service reminder or other reminders until the remaining oil life is less than 80%. Don't ask why, that's just the way BMW programmed the system. I guess they figured nobody would ever replace any components at low mileage, like noisy brake pads or coolant-contaminated oil or a plugged cabin air filter.
The CBS service reminders can be reset using "procedures relevant to supported vehicles." That is BMW's way of saying look up the reset procedure in the vehicle owners manual or on the BMW service information website www.bmwtechinfo.com.
The manual reset procedures do vary depending on the year and model of the BMW, but generally go as follows:
On some, all you have to do is turn the ignition key on (leave the engine off), then press and hold the odometer Reset button. When the service icons appear, press the Reset button again to scroll through the maintenance items, then press the Reset button again to reset each as needed.
On cars with a Start/Stop button, insert the remote control key fob into the ignition slot. Press the Start/Stop button once without touching the brake pedal. Then press and hold the odometer Reset button for about five seconds.
On a 2006 BMW 325i, a menu will appear inside the speedometer display listing the top three service items in the order that service is needed. Be careful not to hold the Reset button in too long, otherwise the instrument cluster will go into a self-test mode and start to display various functions. To exit, just remove the remote key fob from the ignition slot.
To cycle through the menu of service items, tap the Reset button, or press the lower FAS button in the side of the turn signal/high beam stalk on the left side of the steering column. Press and hold the Reset button for a few seconds to reset the highlighted item.
If you have never worked on a late-model BMW, you will be in for a surprise when you try to check the oil on certain models. You can't because there is no dipstick on NG6, N62TU, S65 and S85 engines. The "old-fashioned" dipstick has been replaced with an oil level sensor in the bottom of the oil pan. If the oil level is low, the CBS system illuminates a service reminder light and tells the driver to add oil.
In theory, it is a good idea because most oil warning lights that work off oil pressure don't come on until the crankcase is almost out of oil which may be too late to add oil because the engine has suffered bearing damage. BMW's approach is to alert the driver if the oil level is down more than a quart. Unfortunately, the oil level sensor has been troublesome, sometimes creating false low oil warnings as well as various other driveability issues.
If the sensor is not reading accurately, it may indicate the oil level is low when it is not low. Since there is no way to actually check the oil level in the engine (no dipstick, remember?), most people simply add a quart of oil and wait for the warning light to go out. When the oil level still reads low, they think it needs a second quart, so in goes another quart. You can see where this is going. If the oil sensor is faulty, it may mislead the vehicle owner or a technician into adding too much oil and overfilling the crankcase.
BMW's service procedure for checking the oil level sensor does not require a factory scan tool or any other fancy electronic diagnostics. You simply drain the oil out of the engine, measure it, and then pour the correct amount of oil back into the engine. If the oil level sensor still reads low, replace the sensor and the problem is fixed.
Electronic problems in the CBS oil sensor circuit can also cause other problems. BMW's technical service bulletin SI B 12 33 06 (issued October 2006) describes some of the seemingly unrelated problems that can be traced back to faults in the oil sensor circuit. These include:
Engine won't crank (E46, E53, E83, E85, M54 & N62 models);
Charging system is not working (E53, M54 and M62 models);
"Engine temperature fault" message displayed, but the engine is not running hot or overheating (E60, E63, E64, E66 & N62 models); and
False oxygen sensor fault codes (E60, E63, E64, E66 and N62 models).
All of these seemingly unrelated electrical shorts in the oil sensor circuit or the sensor itself can cause problems. If the oil sensor circuit fuse blows, it also kills power to other systems that share the same power supply (such as the starting circuit and charging circuit). So the fix is to check for a blown fuse in the oil sensor circuit, then track down and repair the fault that caused the fuse to blow (which usually turns out to be a short in the oil sensor wiring or sensor itself).
On E46, E83 and M54 models, check Fuse 30 and also Fuse 9. On E53 and M62 models, check Fuse 5. On E60, E63, E64, E65, E66 and N62 models, check Fuse 008 located in the IVM.
On some 2007 3 Series BMWs (E90, E91, E92 & E93), the CBS system may indicate the brake pads are worn out when in fact they are not. The problem is a software glitch that overestimates the amount of brake pad wear. BMW tech bulletin SI B 32 02 08 (April 2008) covers how to use a factory scan tool to check the CBS estimated brake wear by comparing calculated wear against actual wear. If the two do not match, the fix is to reprogram the Dynamic Stability Control Module with updated software from BMW.
The instrument cluster on many late-model BMWs can also display more than 400 "Check Control" messages, everything from powertrain faults to brake faults to flat tires. BMW tech bulletin SI B 62 06 07 (March 2007) covers instances where the vehicle owner sees a "Check Control" message but the message is no longer displayed. The instrument cluster stores the last 72 messages that were shown, which can be recalled with a factory scan tool, or by turning the ignition on and using the turn signal/high beam switch to display the message codes.