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Help understanding please

Thread starter #1
Hi My name is Paul and I am a diy car/ mechanic / diagnostic freek.


I have some pretty good diagnostic stuff but I am struggling g with the electronics side of the auto electronics. I am looking for someone that would be willing to help me with understanding the basic on a wiring diagram. For instance,

I have a golf 1.9 tdi 2004 and the wiper motor is not working, I have a wiring diagram 3 wires One permanent Live one permanent earth and one from the body control module, Where it must switch the motor on, how can i tell what the wire should send. a live , a earth a signal ect. this is where I am lost. If anyone would be willing to have a look at the drawing and explain how you tell what it should do, I would be most great full


Kind Regards Paul
 

shortbus=

Well-Known Member
#2
Post your wiring diagram. Is the switch itself working? The wiper switch tells the BCM what signal to send to the wiper motor. Did you check all fuses? Even the main ones under the hood, to see if your getting voltage to the motor? Are you getting voltage to the motor?
 
Thread starter #3
Thanks for the reply, M2 is the wiper motor B203 ans B220 is the rain sensor, Not sure if that is fitted to this car, Terminal 4 is the wire that goes to the Body control module. What form of message is sent to the motor? Do i need to scope it?. I have 12v live feed and the earth is good. Is there no way i can test the motor with jumper wires?. golf wiring.png
 

alec_t

Well-Known Member
Most Helpful Member
#4
The symbol for M2 suggests the motor itself contains some electronics, so the wire from the BCM probably applies a logic-level signal to the motor.
 
#7
There are a lot of motor types and its bets if you provide the label of the motor also and a picture of the cables where ever you decide to ask.
 

Diver300

Well-Known Member
#8
The rain sensor and the wiper motor each have a permanent power feed. They come from a wire marked 30 which is probably KL30, which means permanently on. (Explanation here). With that arrangement there would be no way of shutting down the auto wipers with a simple signalling system.

If you have tested the fuses, I would say that you need to use an oscilloscope and see what waveform there is.

I would guess that the motor is connected to a LIN bus or similar.
 
#9
First, it would be a really good idea to disconnect all connections from the motor to the BCM before testing!
Connect the brown wire to ground, then connect the white/red wire to 12v. Then take the signal wire -- the violet/white wire -- and connect it to 12v, and the motor should run.
 

Diver300

Well-Known Member
#10
First, it would be a really good idea to disconnect all connections from the motor to the BCM before testing!
Connect the brown wire to ground, then connect the white/red wire to 12v. Then take the signal wire -- the violet/white wire -- and connect it to 12v, and the motor should run.
I don't think that the signal can be as simple as that. The rain sensor is on the same signal wire as the wiper motor, so there has to be some way for the BCM to turn off the wiper and make the rain sensor take very little power when the car shuts down. There have to be at least these modes:-

Off - with rain sensor only taking minimal power
Off - with rain sensor detecting rain
On - ignoring rain sensor
On - wiper operated by the rain sensor

It's not possible to get all those modes with a single on/off wire.

A LIN signal could do all of those modes. With one message, the BCM would tell the wiper motor whether to run or not, and with a second message, the BCM would ask the rain sensor whether there is rain. The BCM's logic would use the wiper switch position, rains sensor signals, ignition and maybe vehicle speed to decide when to operate the wipers. When the car is turned off, the BCM would stop sending LIN messages, and the wiper and rain sensor would be programmed to detect the lack of messages and to go into low power modes.
 
Last edited:
#12
It's not possible to get all those modes with a single on/off wire.
Take a look at the schematic, it IS a single wire
Many of the signals from the BCM or any computer in a car, are only 5V.
Not in cars, the environment is too noisy for 5v. Besides, ALL control units have protection diodes. 12v won't hurt a thing. AND, I suggested disconnecting everything from the control unit anyway, so your point is moot.
 

alec_t

Well-Known Member
Most Helpful Member
#13
OK what is a logic-level signal and how can i see if it is getting it?.
Generally a voltage (with reference to chassis) which switches between 0V and 5V. Best monitored with an oscilloscope. Do NOT connect 12V to the signal wire, or you'll likely fry the internal electronics in the motor and/or BCM.
 
#14
Do NOT connect 12V to the signal wire, or you'll likely fry the internal electronics in the motor and/or BCM.
Again, it was suggested from the start to disconnect from the BCM!!
Funny how everyone here is suddenly a master auto tech.
12 volts WILL NOT hurt the wiper motor! If you're that afraid of it, then go ahead and try 5v to the signal wire.
There's a lot of pontificating here, and no other answers to the simple original question that the OP posed.
 

shortbus=

Well-Known Member
#15
Not in cars, the environment is too noisy for 5v. Besides, ALL control units have protection diodes.
Have it your way but you would be wrong. Even though the car computers are supplied with the normal "12V" most all of the signals in and out of the computers are only 5V.
 
#17
That's OK, hyedenny will buy him a new one.:)
No he won't because it's most likely the motor anyway. The brushes on them wear out all the time. But perhaps that's something only someone with a long history of professional auto repair might know.
And I'll say it one more time for the reading/comprehension challenged: even if the signal is normally a nominal 5v, putting 12v on the motor's signal input will not hurt it!
 
#18
These cars were common for the transmission linkage seizing up and then the motor couldn't turn them.
I don't think the body computer is involved in this system on this car? I think Volkswagen calls it something like " Thirteen Fold Relay Panel". So the system is controlled by the switch , windshield wiper intermittent regulator , Thirteen Fold Relay Panel and the wiper motor . But I'd check in for seizing or worn out transmission linkage before I'd get my DVOM out.
 

shortbus=

Well-Known Member
#19
After more thought on this, the BCM probably pulls down the third (signal) wire, not supplying a voltage to it. Just like it does with fuel injectors and other things in the vehicle, using a low side switch/mosfet.
 
Thread starter #20
Thanks for all the reply’s, so it seems that I am going to need more information about this 3 wire, I have auto data and that does not give me any help. I will do to the. W golf forum. I was hoping that someone would say it’s easy just look at so and so on the drawing you should be getting xyz from the bcm to switch the wipers on, looks like that is not so, I will report back if ,,,,,no when I find anything out.
Paul
 

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