The ZFE – Charger Handshake

[RadioFlyer]

How often have you seen or heard the term “CAN-bus” in the context of a compatible charger for the accessory socket? Way too often and almost always dead wrong.
“CAN-bus” is probably the most misused term in all of BMW-related forum electrical discussions. While most of the forum discussions are about wiring in farkles this post is about charging via the accessory port.

For an understanding of what the CAN-bus actually is and does I suggest reading the article on Wikipedia.

The ZFE (Zentrale Fahrzeugelektronik or Central Chassis Electrics) is one of several controllers on modern BMW motorcycles. Its job is to manage chassis electrics. It senses logical inputs from switches and responds by turning things (lights, horns, grip heaters…) on and off. It also monitors current draw. If the current draw exceeds a threshold then the circuit is shut down so the ZFE replaces fuses. If the current draw is below a threshold on a light circuit the ZFE assumes that there is a burned out bulb or a wiring fault and tells the Kombi (the instrument cluster) to display a warning. The ZFE manages the accessory port and shuts it down if too much current is drawn (said to be 5A although I have never seen a published figure). The ZFE also monitors the accessory port for the presence of a compatible charger and connects it to the battery for charging.

Compatible chargers are often referred to as “CAN-bus” chargers or some other term using “CAN-bus”. This is nonsense and has led to a great deal of confusion. This misuse of the term “CAN-bus” probably originates with charger vendors. Early on the vendors would characterize chargers as being suitable for “CAN-bus equipped” motorcycles as a way of saying that the motorcycle had a ZFE. Later the terminology morphed into terms like “CAN-bus compatible”, “CAN-bus charger” and “CAN-bus mode”.

The CAN-bus itself does not play a role in charging via the accessory port. That many say it does is part of the mythology.

The ZFE “listens” for a specific electrical handshake from a charger and if the handshake is present the ZFE connects the charger through to the battery. No CAN-bus messaging is required to accomplish this.

Here is what the handshake looks like.

ZFE Charger Handshake.png

A ZFE compatible charger sends and repeats a pulse train to the accessory port. The pulse train starts with the charger presenting 12V to the port for 1 second. Then it waits for 150 milliseconds. Next it sends a series of ten 12V pulses each having a duration of 10 microseconds and spaced 100 milliseconds apart. It repeats this pulse train until it senses that the ZFE has connected it to the battery and then it starts its charging procedure.

Of course you can always attach a charger directly to the battery but BMW instructs you to not do so while the battery is installed in the bike. Why? The reason is that many modern chargers are “smart” and will try to recondition (disulphate) a battery if it decides that the battery needs reconditioning. The desulphation process involves the application of high voltage pulses to the battery and if the battery is connected in the bike then all the bike’s expensive electronics also get exposed to the high voltage pulses as well. So there is some risk of damage involved. BMW isn’t going to try to explain how to determine whether your particular charger has a desulphation capability or not so it just tells you not to charge the battery directly in the bike to mitigate the risk.

If you have a smart charger and intend to connect direct to the battery while the battery is in the bike you should read the charger’s manual to see if the desulphation mode can be disabled. I use the Optimate 4 charger in its “CAN-bus mode” (sic) direct to the battery because in that mode high voltage desulphation is deactivated. I can’t be bothered with charging via the accessory port.

[kthutchinson]

Excellent post. About 12 years ago I started writing an article for the Owners News about similar issues. I never submitted it, but this forum looks like a good place, so here it is.

CANbus and ZFE Misconceptions

Introduction

The Owners News has carried several excellent articles about BMW motorcycle electrical systems. One in particular, by Paul Glaves, appeared in the August 2009 issue. Paul stated in that article that he was not covering the CANbus systems on current BMW motorcycles. This article is my attempt to fill in some of the blanks and explain how the system works and, just as importantly, how it doesn’t work. Since I am an electrical engineer, a certain amount of technical jargon is unavoidable in this discussion, but I have tried to keep it to a minimum.

Many BMW owners, vendors and on-line resources (including BMW dealers and technicians, who should know better) use the term “CANbus electrical system” to refer to the functions of the Zentrale Fahrzeugelektronik (ZFE), or Central Vehicle Electronics control unit, the main control unit for the electrical systems on newer BMW motorcycles. These same people tend to incorrectly blame any electrical anomaly on the CANbus. To some this may be just a matter of semantics. However, the ZFE and the CANbus serve two very different purposes. This article will attempt to explain the functions of the ZFE and the CANbus and, hopefully, eliminate some of the confusion.

CANbus

The Controller Area Network (CAN) bus, or CANbus, is a data network used to allow the various control units to communicate with one another. CANbus was developed by Robert Bosch GmbH in 1983 and first appeared in 1986 on the BMW 8-series coupe. CANbus is used on the R1200s, F800s, K1200s (transverse engine), K1300s, K1600s, and the newer F650GS. My bike is a 2007 R1200ST. Options include Integral Anti-Lock Brake System (ABS) II, Heated Hand Grips, On Board Computer (BC), Tire Pressure Control (TPC), and Automatic Stability Control (ASC). The CANbus on my bike connects the engine Electronics Control Unit (ECU) with the control units for the Instrument Panel (which contains the BC), ABS, TPC, and the ZFE. The purpose of the CANbus is to minimize wiring. Several control units may require the same information. For example, wheel speeds are used by the ABS, the ECU, the Instrument Panel, and the ZFE. Instead of running wires from the wheel speed sensors to all four control units, the wheel speed sensors are only wired to the ABS, which then provides the information to the other units over the CANbus. This simplifies the wiring harness, saving weight and money.

The CANbus, however, is not an electrical system. CANbus transfers data in digital format, not electrical power. CANbus signals are very low amperage, and connecting a conventional 12-volt signal to the bus will probably fry the computers on the bus. To control these higher current signals, BMW has chosen to use the ZFE.

ZFE

When BMW Motorrad introduced CANbus, the electrical systems were also redesigned, and ZFE modules were added. BMW used CANbus in their advertising for these bikes, and the term CANbus electrical system has come into common use, which explains some of the confusion over terminology. The ZFE is simply a power distribution module. It replaces the multitude of relays and fuses found in earlier BMWs. The ZFE receives electrical power from the battery and alternator. It also receives input signals from switches and sensors, and from other control units via the CANbus. Output signals are available to activate such things as lights, horns, and electrically adjustable suspensions. And outputs are sent to other control units over the CANbus. It is important to note, however, that CANbus and the ZFE are independent. A motorcycle can be built with CANbus communication between computers but with a more conventional electrical system with fuses and relays, such as the recent Triumph triples. Or a power distribution module like the ZFE can be used without CANbus communication. Aftermarket power distribution modules are available from vendors such as Aerostich and motogadget for builders of custom motorcycles.

By using logic circuitry, the ZFE eliminates relays. When the ignition key is turned on, ZFE logic keeps the headlights from illuminating until the engine is running. This function was formerly accomplished by the load relief relay. The ZFE monitors the current at each output and shuts down an output when the current exceeds a preset limit. This eliminates the need for fuses. And if the ZFE senses zero current at an output when some current is expected, it can provide a failure indication, such as when a lamp is burned out.

The ZFE can also reconfigure its outputs to accommodate certain failures. My R1200ST has a dual-filament tail light bulb. The low power filament (5 watts) is powered continuously and functions as a tail light, while the high power filament (21 watts) is used for the brake light. Each filament is controlled by its own output from the ZFE. If the tail light filament burns out, the ZFE detects zero current flow and a warning message is displayed on the multifunction display. To temporarily correct the problem, the ZFE powers the brake light filament at reduced voltage so it looks like the tail light, and applies full voltage when the brakes are applied. The reduced voltage is obtained by rapidly pulsing the 12-volt output on and off. If the output is on half the time and off half the time, the filament sees approximately six volts. This technique is called pulse width modulation.

Some ZFE outputs can remain on even after the ignition key is turned off. According to my bike’s Rider’s Manual, the optional accessory socket will remain powered for up to 15 minutes after the ignition is turned off. The exact time depends on the current draw and the state of charge of the battery. The accessory socket will remain on indefinitely when a compatible BMW battery charger is connected and operating. BMW has not released a description of the logic used by the ZFE to determine how long to power accessories from the battery, and web forums have reported several instances of dead batteries due to accessories remaining powered after the motorcycle had been shut down. Therefore, best practice is to ensure that all accessories are off and even disconnected prior to walking away from your motorcycle.

[RadioFlyer]

Great article. More exposure to this kind of thing is woefully needed.

Sent from my SM-T813 using Tapatalk

[dieselyoda]

CAN-Bus has been used well over 15 years now.

A few things you must know:

The ignition/start/headlights and so on are activated by the Controller by grounding the circuits.

It does sense current load by way of Multiplex Wiring.

You need to have bidirectional communication to determine your faults and clear faults.

Save your last known download of the controller to a .txt/.xls.

This is not specific to BMW Motorcycles but there is a ton of equipment out there from yellow iron to every class of truck and the family car that use CAN-Bus.

So far, the posts have been very helpful but as some of you have seen my post on troubleshooting; Fuses(pull them and inspect, all of them) and grounds.

We repair more equipment by doing those simple things than charging $500.00 just to connect with a scan tool.

[RadioFlyer]

CAN-Bus has been used well over 15 years now.

A few things you must know:

The ignition/start/headlights and so on are activated by the Controller by grounding the circuits.

It does sense current load by way of Multiplex Wiring.

You need to have bidirectional communication to determine your faults and clear faults.

Save your last known download of the controller to a .txt/.xls.

This is not specific to BMW Motorcycles but there is a ton of equipment out there from yellow iron to every class of truck and the family car that use CAN-Bus.

So far, the posts have been very helpful but as some of you have seen my post on troubleshooting; Fuses(pull them and inspect, all of them) and grounds.

We repair more equipment by doing those simple things than charging $500.00 just to connect with a scan tool.

There is so much misinformation and/or confusion in this post that I don't know where to begin.

The ZFE does NOT ground devices to activate them. It supplies power to them. The devices have wires going directly to ground.

The ZFE does not sense current using "multiplex wiring".

Except for a main fuse on certain later model bikes there are no fuses to pull on bikes with ZFEs.

The rest of this disjointed post seems to deal with diagnostics which has nothing to do with the subject matter of the thread.

[dieselyoda]

There is so much misinformation and/or confusion in this post that I don't know where to begin.

The ZFE does NOT ground devices to activate them. It supplies power to them. The devices have wires going directly to ground.

The ZFE does not sense current using "multiplex wiring".

Except for a main fuse on certain later model bikes there are no fuses to pull on bikes with ZFEs.

The rest of this disjointed post seems to deal with diagnostics which has nothing to do with the subject matter of the thread.

I'm not gonna argue that you are right. You may well be absolutely correct on BMW Motorcycles.

We do $12M a year and we are just a repair shop. Everything we see with CAN also use Multiplex wiring.

We do CAT, Komatsu, Deere, some Case and a fair amount of Freightshakers, Corn Binders and some Paccar(Kennie's and Pete's) and lately Autocar.

My post was not meant to be adversarial(my message was my message, how you interpreted it isn't my fault).

I am not a BMW trained mechanic and I just may have relied on my experiences from my 40+ years as a pro-wrench to fix the few BMW Motorcycles that come my way with CAN -Bus.

I never argued your post. Why are you taking exception to what I posted when I very clearly said, "I don't have experience with ZFE."?

My post was strictly to add my experience. So far though, I have never seen a controller provide "hot power".

Have a good New Year and I will be adding this post to the reasons why the BMWMOA is no longer a value to me.

[RadioFlyer]

I never argued your post. Why are you taking exception to what I posted when I very clearly said, "I don't have experience with ZFE."?

My post was strictly to add my experience. So far though, I have never seen a controller provide "hot power".

I take exception to misinformation and disinformation. My post and the one that followed were specicifically written to combat misinformation.

Here is a typical situation where the ZFE powers a device. Note that both turn signals are grounded and that power is being supplied by the ZFE.

ZFE Powering Turn Signals.jpg

[dieselyoda]

I take exception to misinformation and disinformation. My post and the one that followed were specicifically written to combat misinformation.

Here is a typical situation where the ZFE powers a device. Note that both turn signals are grounded and that power is being supplied by the ZFE.

ZFE Powering Turn Signals.jpg

Did you read my comments that I have NO experience with ZFE?

It's entirely my responsibility to write a message that is clear and accurate. It's up to you to determine the meaning of what I write.

My point was to simply share my 40+ years as a PROFESSIONAL HEAVY DUTY MECHANIC THAT IS CERTIFIED ON EVERY PIECE OF YELLOW IRON, CLASS 8 AND LOWER TRUCKS that has 21 HD Mechanics under my umbrella

I'm outta here. Enough BS.

[OldCamper]

I was under the mistaken impression that the canbus wire provided both the control signal AND the power, kind of like power over Ethernet. I’m a bit disappointed to learn it requires a separate power distribution unit, and then individual power wires to devices, which seems to add more complexity than it’s worth. What could possibly go wrong with such a system?

I suppose there must be some benefit though, as I understand it’s common in cars these days.

Regardless, I wouldn’t want it on my bike if given the choice. Simple is good. Why mess with what works?

[skag]

Loved your explanation. Very nice job!

Excellent post. About 12 years ago I started writing an article for the Owners News about similar issues. I never submitted it, but this forum looks like a good place, so here it is.

CANbus and ZFE Misconceptions

Introduction

The Owners News has carried several excellent articles about BMW motorcycle electrical systems. One in particular, by Paul Glaves, appeared in the August 2009 issue. Paul stated in that article that he was not covering the CANbus systems on current BMW motorcycles. This article is my attempt to fill in some of the blanks and explain how the system works and, just as importantly, how it doesn’t work. Since I am an electrical engineer, a certain amount of technical jargon is unavoidable in this discussion, but I have tried to keep it to a minimum.

Many BMW owners, vendors and on-line resources (including BMW dealers and technicians, who should know better) use the term “CANbus electrical system” to refer to the functions of the Zentrale Fahrzeugelektronik (ZFE), or Central Vehicle Electronics control unit, the main control unit for the electrical systems on newer BMW motorcycles. These same people tend to incorrectly blame any electrical anomaly on the CANbus. To some this may be just a matter of semantics. However, the ZFE and the CANbus serve two very different purposes. This article will attempt to explain the functions of the ZFE and the CANbus and, hopefully, eliminate some of the confusion.

CANbus

The Controller Area Network (CAN) bus, or CANbus, is a data network used to allow the various control units to communicate with one another. CANbus was developed by Robert Bosch GmbH in 1983 and first appeared in 1986 on the BMW 8-series coupe. CANbus is used on the R1200s, F800s, K1200s (transverse engine), K1300s, K1600s, and the newer F650GS. My bike is a 2007 R1200ST. Options include Integral Anti-Lock Brake System (ABS) II, Heated Hand Grips, On Board Computer (BC), Tire Pressure Control (TPC), and Automatic Stability Control (ASC). The CANbus on my bike connects the engine Electronics Control Unit (ECU) with the control units for the Instrument Panel (which contains the BC), ABS, TPC, and the ZFE. The purpose of the CANbus is to minimize wiring. Several control units may require the same information. For example, wheel speeds are used by the ABS, the ECU, the Instrument Panel, and the ZFE. Instead of running wires from the wheel speed sensors to all four control units, the wheel speed sensors are only wired to the ABS, which then provides the information to the other units over the CANbus. This simplifies the wiring harness, saving weight and money.

The CANbus, however, is not an electrical system. CANbus transfers data in digital format, not electrical power. CANbus signals are very low amperage, and connecting a conventional 12-volt signal to the bus will probably fry the computers on the bus. To control these higher current signals, BMW has chosen to use the ZFE.

ZFE

When BMW Motorrad introduced CANbus, the electrical systems were also redesigned, and ZFE modules were added. BMW used CANbus in their advertising for these bikes, and the term CANbus electrical system has come into common use, which explains some of the confusion over terminology. The ZFE is simply a power distribution module. It replaces the multitude of relays and fuses found in earlier BMWs. The ZFE receives electrical power from the battery and alternator. It also receives input signals from switches and sensors, and from other control units via the CANbus. Output signals are available to activate such things as lights, horns, and electrically adjustable suspensions. And outputs are sent to other control units over the CANbus. It is important to note, however, that CANbus and the ZFE are independent. A motorcycle can be built with CANbus communication between computers but with a more conventional electrical system with fuses and relays, such as the recent Triumph triples. Or a power distribution module like the ZFE can be used without CANbus communication. Aftermarket power distribution modules are available from vendors such as Aerostich and motogadget for builders of custom motorcycles.

By using logic circuitry, the ZFE eliminates relays. When the ignition key is turned on, ZFE logic keeps the headlights from illuminating until the engine is running. This function was formerly accomplished by the load relief relay. The ZFE monitors the current at each output and shuts down an output when the current exceeds a preset limit. This eliminates the need for fuses. And if the ZFE senses zero current at an output when some current is expected, it can provide a failure indication, such as when a lamp is burned out.

The ZFE can also reconfigure its outputs to accommodate certain failures. My R1200ST has a dual-filament tail light bulb. The low power filament (5 watts) is powered continuously and functions as a tail light, while the high power filament (21 watts) is used for the brake light. Each filament is controlled by its own output from the ZFE. If the tail light filament burns out, the ZFE detects zero current flow and a warning message is displayed on the multifunction display. To temporarily correct the problem, the ZFE powers the brake light filament at reduced voltage so it looks like the tail light, and applies full voltage when the brakes are applied. The reduced voltage is obtained by rapidly pulsing the 12-volt output on and off. If the output is on half the time and off half the time, the filament sees approximately six volts. This technique is called pulse width modulation.

Some ZFE outputs can remain on even after the ignition key is turned off. According to my bike’s Rider’s Manual, the optional accessory socket will remain powered for up to 15 minutes after the ignition is turned off. The exact time depends on the current draw and the state of charge of the battery. The accessory socket will remain on indefinitely when a compatible BMW battery charger is connected and operating. BMW has not released a description of the logic used by the ZFE to determine how long to power accessories from the battery, and web forums have reported several instances of dead batteries due to accessories remaining powered after the motorcycle had been shut down. Therefore, best practice is to ensure that all accessories are off and even disconnected prior to walking away from your motorcycle.

[RadioFlyer]

For anyone reading this that has a late model bike with LIN-bus please note that there are important differences. The ZFE may not switch all devices. For example a LED headlight may be connected to the LIN-bus and be commanded to come on rather than being switched on in the conventional sense.

[wkoppa]

Fuses(pull them and inspect, all of them) and grounds.

Amen.

Was at Anderwerks in Calgary on my way north.

Suddenly had a circuit not working.

They stayed after trying to figure what was happening.

Fuse looked good. It was not.

Wasted a lot of time not changing out the fuse first.


Wayne Koppa
Grayling, MI
#71,449

[CajunRider]

Fuse looked good. It was not.

Wayne Koppa
Grayling, MI
#71,449

If you ever see a tech LOOK at a fuse and say it's good, find a different tech.

One should, at a MINIMUM, put a multi-meter on a fuse to test it for continuity. Ideally, test it live (with current passing through it) checking for voltage in/out the fuse block (not always easy on factory blocks).