Brake switch implausible signal
- Thread starter LordTJC
- Start date
audifan
A2OC Donor
Again stating the obvious but you have correctly refitted the wiring plug to the switch? Have a good look at the brake pedal to see if there is something wrong with that. Place a phone or camera and film the action of the pedal pressing the switch to see if there is something wrong there.
No offence taken. I have just checked and it is definitely the brake switch I have changed. The clutch switch is vertical, whereas I can see the horizontal one I replaced moving when I push the brake pedal. Picture attached. It’s the one with the red wires go into it.
Thanks.
Attachments
PlasticMac
Member
Good spot Sir, does look as if it needs to be unplugged, and that pin needs pushing in to latch it in the socket moulding.
Mac.
That’s a good idea. Unfortunately I’ve just made sure all the pins are fully inserted and it’s made no difference. On the other end of the plug I can see they are all equal.
The mystery continues!
PlasticMac
Member
If that pin was not latched into the socket body, it could pull through when you unplug it. Clutching at straws, I know, but with it unplugged try to pull the red wire out, from the back but gently. If it moves push it firmly back in, until you feel it latch. If it does move, I'll, as they say, get my hat.
Mac.
Thanks for all the help so far everyone. I have tried pulling the wires from the back of the plug, they move a small amount and then stop, so I think they are clipped into the plug correctly.
I have tried refitting the Febi switch, this time while the brake pedal is pushed down, and then releasing the pedal onto the plunger. I know it’s not the correct method but wanted to rule out the plunger not contacting the pedal mechanism. This didn’t work either.
I have looked at the 003 measuring block on the ABS ECU. I can see two channels activating when I push the brake pedal. However, one channel activates first, and the other when I push the pedal harder. Should they be activated at the same time? I assume one is for the lights and one for the ECU.
Is there any other live data worth checking in VCDS?
I have tried refitting the Febi switch, this time while the brake pedal is pushed down, and then releasing the pedal onto the plunger. I know it’s not the correct method but wanted to rule out the plunger not contacting the pedal mechanism. This didn’t work either.
I have looked at the 003 measuring block on the ABS ECU. I can see two channels activating when I push the brake pedal. However, one channel activates first, and the other when I push the pedal harder. Should they be activated at the same time? I assume one is for the lights and one for the ECU.
Is there any other live data worth checking in VCDS?
chubbybrown
Member
as a curve ball are the Brake light bulbs standard ones along with the LED working?
PlasticMac
Member
Looking at the schematic, both switches go to the ECU. With the pedal at rest the switch pins 1 and 4 (red/brown and red black) are open circuit, while pins 2 and 3 (red/green and white/red) are closed. This is how the switch should be before it's fitted. When pressed, 1 and 4 go open, while 2 and 3 close.
Again, not to insult, but you are clearing the faults (on VCDS) each time?
Mac.
Thanks. The faults on VCDS won’t clear when I try.
I’ve also looked at 006 on the engine ECU. Without touching the pedal the clutch/brake switches show 010, I think it’s meant to be 000? With the brake pedal pressed it’s showing 011 which is correct. Not sure if this helps narrow it down though.
Yes standard spec bulbs and the high level light is also working correctly. I’ve replaced the bulbs to be sure too.
PlasticMac
Member
Check your spare switch with a meter, to see if it conforms to "With the pedal at rest the switch pins 1 and 4 (red/brown and red black) are open circuit, while pins 2 and 3 (red/green and white/red) are closed.
You could link pins 2 and 3 on the connector, this would mimic the switch, as it should be, If the fault does not clear, then maybe it's not the switch at all.
I also think the switch shares the ground behind the headlight ...
Mac.
Howey
Member
Good info but imagine the earth point is on the n/s/f footwell, could a temp earth be added to the switch?
PlasticMac
Member
I'll look at the schematic again later, Im sure I saw a reference to the ground behind headlight though.
A temp earth would rule the ground out, or in for sure.
Mac.
Had a similar issue, changed switch but problem was still there. Turned out that current leaked over to the brake circuit via right side rear light assembly. Path was to high resistance to actually turn on the lights, but resulting voltage apparently triggered an error. Took it apart and cleaned. Problem disappeared
audifan
A2OC Donor
Mac are you getting confused between the main earth lead between the chassis and starter which bolts below the left headlight and the earth connection point for the left headlight wiring?
I would now be concentrating more on the rear bulbs for correct fitment, corrosion, loose contacts, worn contacts on the bulbs, dampness and earth issues.
I would now be concentrating more on the rear bulbs for correct fitment, corrosion, loose contacts, worn contacts on the bulbs, dampness and earth issues.
PlasticMac
Member
See attached snips from the electrical schematic, one side of the switch is connected to ground, which is labeled 176. in the table, 176 is identified as "earth connection behind right hand headlight" items are not always connected to the nearest earth point, but will follow the route of the loom.
Mac.
Mac.