Breake Switches

Brake Switches

00741 - Brake Pedal Monitoring
27-00 - Implausible Signal

I got the following error. My brake pedal has 2 switches and 3 wire plugs
During the conversion I keep the original brake switch that active only the brake lights. When I passed the TDI wiring I putted the blue switch and connected it. The wire plug that connects to the brake light switch of the TDI wiring is unplugged. I think this the reason for the error since the ECU only receives the signal from one switch.

1- Would like to know if I can connect the wire from the TDI brake light to the wire of the original brake light to stop the error and be able to add the cruise control feature.
2- I also would like to know how to setup the length for the blue switch that connects to the T80/9 on the ECU.

João

My G60 Corrado used two switches before the TDI conversion. 1 was for the lights and other was for the cruise control.

The Corrado after swapping in a mk3 AHU used two switches. 1 was for the brake lights and the other was for the ECU (cruise control and some other ecu items)

If the ECU does not get the brake switch signal it will throw a code and this code will cause a flashing glowplug light. My car after the swap had a brake light switch fail and the gp light would flash at me. You can strill drive the car but the ECU is check both of them. I can't remember how the brake light switch is wired but the ECU does monitor both of them.

To set the proper length you need to be able to see at what hiegth the contacts open and close and adjust them so they open and close at the same time. The Mk4 switches combined the switches together.

If you have access to a VW/Audi scanner, VagCom (now VCDS) or similar, check the page showing brake switch operation.
The brake lever operates two switches. One switch is for the cruise control. The second switch is 'split' and operates the brake lamps AND sends an input to the ECU.

You'll need switches "F" (brake lamps), "F36"(interrupt from clutch pedal), and "F47" (interrupt from brake pedal).
On the 68 pin ECU (1Z and AHU), the brake switch "F" sends electrical current through the two brake lamps and also to the ABS and the ECU. The electrical schematics for these additional circuits are located in the engine management section, not in the brake lamp wiring, in my generation of Bentley manuals.
It took me months to locate the connector between the "F" output, and the pin 44/68 input so that the ECU would allow cruise operation and eliminated the implausible brake pedal monitor.
Check to be sure that your 80 pin ECU doesn't have one of these semi-hidden circuits the way mine did.

G60ING said:

I can't remember how the brake light switch is wired but the ECU does monitor both of them.

Click to expand...

That is one of the things, that I would like to know

João

Lug_Nut said:

Check to be sure that your 80 pin ECU doesn't have one of these semi-hidden circuits the way mine did.

Click to expand...

Thanks for the input. "F36"(interrupt from clutch pedal) and "F47" (interrupt from brake pedal) are installed. I can seem on the Elsa that there is a connection to the T80/20 when I brake.

So do you think that I can connect the ro/sw from "F" to the output connector of the brake switch that I have? I only have 2 brake lights but the ECU is checking 3. Can I have problems with that?

M21, M22 and M25 are the brake lights
J... must be the ABS module
D73 positive connection on the engine compartment
J248 ECU
|7| goes to the fuse box

I don't have the wiring in front of me, but I remember the ECU gets a ground through the brake lights when they are off. Until I solved that, I was getting the same error. In my case I was trying to use the original master cylinder switches to send the signal to the ECU. I ended up installing a 2 way switch from a new beetle and wiring it as needed. When the brake lights are lit, power is supplied to the ECU. When the brake lights are off, the ecu is getting a ground through the filaments. mark

JoaoT4 said:

"F36"(interrupt from clutch pedal) and "F47" (interrupt from brake pedal) are installed. I can seem on the Elsa that there is a connection to the T80/20 when I brake.

Click to expand...

If this is similar to the A3/B4 68 pin ECU, there is a wiring connection between the brake switch and the ABS. You need to find that.
D73 is not "positive", that is it is not connected to the battery + terminal, unless the brake pedal switch is closed. D73 is simply a junction connecting the output from the "F" switch to the 80/20 ECU input and the three (or two if that's all you have) brake lamps, and to the "J whatever" ABS module.
Find the wiring for the ABS module and determine which input comes to it from the brake switch.

(Sorry, The only 80 pin ECU schematic I have is for a 1998 New Beetle and it's entirely different.)

Lug_Nut said:

Find the wiring for the ABS module and determine which input comes to it from the brake switch.

Click to expand...

On the A3/B4 68 pin ECU which input do you have on the wiring schematic? It must be similar.
I think that the rest is right connected.

João

rsxsr said:

When the brake lights are lit, power is supplied to the ECU. When the brake lights are off, the ecu is getting a ground through the filaments. mark

Click to expand...

Mark that is the way I have now. For a while I didn't get the error I was happy, because I thought I had found the solution, but the error got back. I deleted again and it didn't come back. Let’s see what errors I will have tomorrow. Also the J... connection is confusing me because I don't know what to do with it.

João

The error returned after a while. I will try to replace the two switches by the 2 way switch. I need to know if the hole for the brake light switch is the same for the 2 way switch.
I also would appreciate if someone has the wiring pinout for the 2 way switch.

João

The wiring diagram makes it look like there are two switches, but it is actually the wiring for a single switch.

Don't know about the mounting hole. I had to make a bracket from scratch on the vanagon. The switch is a little odd in the way that you set/adjust it.

I went to a junk yard and I got a Plug and the switch for free. I will have to check how to connect the wires. The electric plug has the numbers1, 2, 3 and 4. I know that the one that is closed is for the cruise and the one is open is for the lights. Do you know if 1 and 2 is one switch and 3 and 4 is the other?

João

From memory the switch is wired left to right and yes the first two positions are for the one switch and the second pair are for the other. You can verify the function with an ohm meter. One switch is open when at rest and the other is closed at rest. The functions reverse when the switch is operated. Remember, the switch when out of the bracket is "on" when testing. When installed the pedal closes the switch.

Brake lamps contacts are normally closed, but are held open (lamps not lit) when the brake pedal is up.
Cruise control contacts are normally open, but are held closed (circuit complete) when the brake pedal is up.

FYI

On the electric plug

1 and 4 are for F switch
2 and 3 for F47 switch

I will try to install the plug today after I get a tool to remove the wires from the plug to avoid cut and welding the wires.

João

I can't find the problem. I have replaced the two switchs by one and used two diferent models.

These are errors that I have:

VAG-COM Version: Release 311.2-N
Control Module Part Number: 038 906 018 EC
Component and/or Version: 1,9l R4 EDC 0200SG 2147
Software Coding: 00002
Work Shop Code: WSC 02009
3 Faults Found:
18025 - Glow Plug Pre-Heat Indicator (K29): Open or Short to Ground
P1617 - 35-10 - - - Intermittent
00741 - Brake Pedal Monitoring
27-00 - Implausible Signal
01117 - Generator Terminal DF Load Signal
27-00 - Implausible Signal

João

I have made 6500km these holidays with no problems and I'm happy with that . I went to Spain France, Italy, Austria, Switzerlandand Germany.
My problem is that I would like to remove the brake light switch error. If the ECU gets a ground through the brake lights witch is the electric resistance that the ECU must check to see if the light are ok? I also don't have the glow plug light connected if that matters.

João

This is what I have. I think that I should have 000 insted of 001.



The first is clutch and the other two are the brake switch. Is it right?

João

The label for the switches on the VAG-COM is not on the correct order. Does anyone know the correct order?

(F36/F47/F) ????


João

PS: The word brake is miswritten on the topic name and I can’t correct it.

I found the problem. I can’t believe that I made such a mistake. Instead of checking the wire colors I used a voltmeter. Since one wire was with 11.8V I thought that was the wire from battery. I was wrong, because a wire from battery has 12.3V. This wire is the one that is connected to the ECU to check if the rear lights are OK. As soon I ground it the F switch went to 0
Thank you for the help. By reading your replies I figure out that I had made a mistake, because in theory everything was right. I was being a bit lazy to check the wires, because they were covered with tape

João