Honda multiplexing Board and CAN signal pattern

This is a low speed CAN multiplexing used for body control in Honda. It utilizes a 3-node control units for driver's door, driver's side and passenger side. Now the basic of electronics is always Input-Control Unit-Output. Talking about body control means window motors, lights switches & indicators, wipers etc... So on the board we also have parts that are used to simulate the car's body, this one particularly is door control.

The testing procedure to see whether if this CAN multiplexing system works properly on window motors or not, is divided into 3 level: Communication lines and nodes(mode1); inputs(mode2); mode3: must be output. Note that these are not exactly how we should diagnose a real car body control unit, but similar in concept.

To proceed into mode1, basic preliminary check must be done, using the provided wiring diagram, we must identified all the pins numbers and wire colors for the communication lines between the nodes, and between power supply to each modules and their earths.

When a fictional fault is created, we don't know the fault or having any clue so best is to check every buttons(inputs) to see if they are OK. When a fault is spotted that a rear window motor on the driver side only spins one way(window up) but not the reverse, test procedure 1 is now carried out.

The board is designed so that we have a fault light that doesn't light when an input or communication line is malfunction. All we need to do now is try switching the window down button that wouldn't work. If the test light comes on then we haven't found our source yet. But if it stays off, that gives us a clue to recheck the communication wires from  nodes, to the motor's relay, and that means the power & earth side as well. Of course, when checking the faulty window button, re-checking other input buttons is not a bad idea, other faults could also be found and it will even give us more clue where to look next.

Mode 2: this is the input check mode - that means if there is no continuity between door switches and the power side of the motor, that the switches are malfunction, then the check light should not light and there will be no BEEP!.....The switch beeps the system, so we had to check the relays and the motor's wiring.
Because each window uses 1 motor, so that motor will be wired so that the current will flow backwards when going up or down. Finally, we had to trace to the motor and reconnect the reverse power wire to ground. And we re-check the rear reverse motor, it works again.

The CAN signal pattern.

 What you see is a standard awake multiplex signal...with aliasing. As mentioned on the Land Rover CAN system earlier, aliasing is when the "ghost signal" overrides the "real signal". When observing, it is important to set your oscilloscope to a suitable time and Voltage division, to be able to spot aliasing as easy as possible. The ghost signal tends to flash over the real signal, which seems to stay more solid, and you have to observe over a period of time. So when you are certain which one is which, use your own visual processing to choose the right signal patterns you capture.

 Unfortunately, the CAN signal pattern is not as easy to obtain as any other diagnostic codes, because they communicate really fast. Still, we can identify the difference between an "idle"(not idling engine) awake signal pattern and the switched(communicating) pattern, well, by focusing.

 When switches(a brake light switch), the pattern will change a little bit. And of course, the high CAN and low CAN always mirrors each other.




 

CAN-Multiplexing worksheet On Car – Range Rover 2001

We all know that Range Rover is a very prestige stream, yet the brand is popular in numbers as well. Like a BMW SUV, the Range Rover 2001 uses the same engine management system as the series 5 E39 2001, and of course, it holds a very advanced CANBUS system which makes automatic communication and user’s comfort as efficient as possible.

The CANBUS system is like a universal communication language on vehicle’s electrical management, therefore it can be anywhere on a car from ECM, TCM to accessories etc… With this one, we take a look at the CANBUS for the ABS system.

Identifying wires are phenomenon, we would be expecting any “twisted pair” wires. This is because when 2 wires are twisted along each other, their magnetic field interferences cancel out each other, giving a clear signal.

The type of signal we expect from these types of wire is quite special as well. There will be a CAN HIGH and CAN LOW mirroring each other in signal. The signal is pretty much digital signal, one towards a CAN module which called a “node”; and one in vice versa to the first module, the two go back and forth.

CAN HIGH is the signal which starts with a relatively low voltage and switches to higher voltage when it needs to communicate. To the ECU, it’s like start normally zero and communicating by 1.

CAN LOW starts with a relatively high voltage but then grounded to low or zero voltage when it communicates. It’s like start 1 and then jump down to zero.

An oscilloscope with a dual trace setup can help us capture this signal on sight. Voltage and time division and be set to avoid “aliasing”. Aliasing is a term in CANBUS signal which describes a condition where there is a “ghost” signal frequently appearing out of phase with the “real” consistent signal. In prior to capture the signal by pressing HOLD, the aliasing can alter the real signal, giving us falsified CANBUS behavior and THIS jeopardizes CANBUS diagnostic.

Although Oscilloscope is easy and quick to set up to test the CANBUS but this is just a small test and you can only test one “twisted pair” at a time. Therefore we use scan tool as also a main device that gives us a general fault codes condition and actuation of the “WHOLE” system. A mislead is to try to find the CAN system after selecting brand and model. This is pointless because the CANBUS IS the language that communicates between systems from high speed CAN to low speed CAN and to the users that we can receive all the engine check lights and trouble codes when we turn on our scan tool.

Also, a misunderstanding is HIGH speed CAN and CAN HIGH, they are different by definition. High speed CAN is systems that runs on real time in prior to systems that affect mobility and safety of the vehicle(engine, transmission, ABS, Traction and stability control, auto door-lock, Inhibitor switch etc…) and Low speed CAN, you know, accessories in prior to user’s utilities(radio, CD players, windows, wipers, horns…)

There is a SLEEP MODE on the CAN systems, which allows the whole CANBUS to go to sleep, which means not communicating after a few seconds. This amount of time is for the nodes to collect and memorize all the necessary data before going to “sleep”, and it goes to sleep even when the ignition is OFF in prior to not losing all the data which is very useful for making the next start more efficient. Sleep mode replaces OFF mode for not draining battery overnight.

Anti-lock braking system ON-car

  All modern passenger automobiles now have ABS. This provides faster stopping and safer steerability for regular drivers at most driving situation and road conditions(except gravel, dirt, snow...)
  Most ABS systems have a standard layout of: ABS ECU; Hydraulic control module; and Wheel speed sensors(all wheels have WSS)
  Because ABS is ECU controlled, it is wise to understand the circuitry of operation of the ABS.
  In a wiring diagram practice, the point is to have the ability to identify which wire is which: by colors and pin numbers. It is important to identify the control wire from the ECU, or the power side from the ABS relays, or which solenoid is which pin number etc...
In the ABS wheel sensor, the reason for the braided wire is to prevent interference from external radio signal; or inductance from other close high amperage wires.
 
For each individual wheel, the ABS system pretty much just actuates the Fluid Inlet and Outlet Valve, to control the brake pressure and free wheel under its own programmed style.
  Under normal braking: The Inlet valve opens also the Outlet valve opens, this doesn't diminish the brake pressure because the pump is running as well, so brake pressure increases as much as enough for the wheels to lock.
  When ABS system kicks in is when the brake system is about to lock the wheels, as the driver depresses the brake up to a point where ABS kicks in. Then, these 3 periods of ABS operation take place as 1 cycle of ABS braking, given that the driver still keeps his foot on full brake during the whole brake length:
1. Reduction: Inlet valve closes, Outlet valve opens in order to reduce brake pressure.
2. Hold: While break pressure is decreasing, it is then necessary to hold that low pressure by keeping both valves closed, so wheels can turn and this provides steerability.
3.Increase: Inlet valve opens, outlet valve closes, this in prior to the pump will accumulate the fluid pressure, causing the wheel to be locked up again, and the whole cycle repeats until the car safely stops.

A misconception that the circuitry part of the ABS is quite troublesome, wrong, the ECU is robust and almost never give any problem, it is the hydraulic, mechanical side that sometimes get clogged up, stuck Opened or Closed that fail ABS. Especially, the wheel speed sensor is the most frequent cause of ABS failure, simply because the if the mechanism is damaged, then the signal is unclear to the ECU.

WSS: same concept into the crank or cam sensor: they can be reluctor, hall-effect, Photo-sensitive etc….

Let’s look at the reluctor WSS:

This consists mainly of a tooth wheel that rotates with the wheel’s speed and a magnetic pickup. Whenever a tooth moves closer and closest and starts moving away, it induces a sine wave signal through the pickup, and that goes to ECU as the ABS’s input.

In order to perform this check, first get a car on a hoist, remove the wheels, bring the car up, then the sensor mechanism can be worked on easily. Then use an oscilloscope to examine the signal that theoretically it should give:

This is a very important step in diagnostic, because the signal waves pretty much tells everything about how good the sensor is working. A visual check is also important, it helps spot out the obvious faults and can be prevented from future failure. When a signal is not as good as it should be, then one of the problem could be the gap between the tooth (at closest position) and the pickup magnet. Using a metal feeler tongue would damage the sensor, therefore a brass tongue should be used. The part that gets damage is the braided cover that prevents interference from other radio signals, also removing noises, this protects the clarity for the signal.

Unfortunately, we were not able to get the Mazda Familia ABS actuator screen on scan tool, but we got the diagnosis screen:

There are 5 faults, mostly dedicated to the 4 WSS. Because this is FWD, and we hoisted the car up to run the front wheels, therefore the rear wheels were not spinning, only if they are on the ground. The ECU normally gets all 4 wheels spinning @ same speed for the test but now it thinks that there is a fault that the 2 rear wheels didn’t transfer any signal.

WS2 & WS5 Flash Codes & Scan Tool Diagnostics

These are 2 quickest ways without getting your hands dirty without knowing where to look.

With flash codes, you are resorted to a standard procedure for dealing with problems which are relatively simple or just eliminating possibilities. Because once your car experience a malfunction that the engine doesn't sound as normal as it uses to be, you either know nothing about it or there are 2 many possible causes. That is when you turn the key on and the engine check light on the dash board is On, and doesn't turn off as the engine starts, you panic.

It's always best to have your own car's service manual, or not, insurance. Toyota is very open with car service manuals, so here we will test diagnostic with a 4A-FE 1999.
Procedure: Find the Diagnosis Plug(named on it), bridge E1 and TE1 using a piece of wire.
                  Ignition on, Engine OFF, Check engine light should flash frequently and will turn off when Engine is ON if there is no fault codes in the memory.
                  If there is any code, the light will flash accordingly: long pause-1st digit flashes-2nd digit flashes-long pause-repeat.

To make sure this system works correctly, we ask our tutor to create some faults, so then this will feel anonymous. When attempting to find the problem using diagnostic trouble codes(DTC), do a visual inspection after receiving the codes, after the faults were created, for example:
For the codes we get:

Code Number	System Affected	Condition described
41	TPS	Throttle position sensor circuit
22	THW	Water temperature circuit
31	Vacuum sensor	Vacuum sensor circuit

Loose connections in all 3 systems, all codes describe circuit problem, which is more likely to be connection problems=> So this is how we traced back to where exactly have gone wrong. Some time, the troubles are obvious that can be spotted by visual inspection. Sometime, electrical testing is carried out, only when we know where or the type of system involving - this is the kind of information the DTC is helpful about.

After repairing the fault, it is also important to clear the trouble codes, because it takes memory that we don't want into the system. Here is the procedure to clear the codes in DTC dignosis:
Turn off the engine
Switch Ignition Key off
Disconnect the battery
Wait 30seconds
Reconnect the battery and Ignition on
Check the Engine check light if it is flashing normally
Run the engine for the engine light to turn off
Make sure the codes are cleared.

Faults on any system of the Engine Management System will always affect engine's performance and efficiency, and safety one way or another. For example:
TPS unplugged: There is an Idle switch and a WOT switch, which will never be signaled to ECU, so at idle, ECU won't give out the best lambda mixture, or causes hesitation or lack of power when accelerating because ECU doesn't know where the throttle is exactly and the WOT switch is never on.

Scan tool Diagnostics
Unlike the DTC that differs from car to car, the Scan tool is the professional way to find faults in vehicle, in workshops, they are used by qualified auto electricians. 
There are somethings to take note about this device: First, it is very expensive and it comes as a package to adapt on ANY model of modern vehicles. So when you try to find the ECU plug on your car you'd better find the right shape of adapter as well. Secondly, if you want to diagnose your car you must find the right brand, right model and the right year to start diagnose on the scan tool.
There are many features available on this specialized computer: Fault codes finding, Actuators testing, Live data sensors screen, which let you see the live data when the engine is running, coming from every sensor of the car, this is what it looks like:

When there are faults in the system, for just a few clicks, we can see it, with more details than the DTC method:

With the live data feature, we can record the old normal data and compare it with the new data that the faults affect, and with the exact reading-by-sensor, you are pretty much sure about what is going on:

Type of information(PID = Parameter Identification	Letters to describe it	Value of data (normal)	Value of data (faulty)	Units
Intake manifold	-	14.6	31	Kpa
ISC Duty	-	10.09	7.7	%
Output volume of FR	O2 sensor	0.9	0.2	V

From here proceed with standard inspecting and repairing faults.
One more thing about the scan tool that is similar to the DTC system, that is clearing codes. One connected, the Scan tool displays the soul of the ECU, so they are pretty much in sync, therefore clearing codes is a must, and not hard, just few clicks away.
After clearing the codes, restart the scan tool and check for codes to make sure codes are cleared.

Clearly, the scan tool aid us from where to fix to reducing time of fault finding. Making it faster for simple problems and easier, more approachable for deeper, more sophisticated problems.