Really weird electrical snag!

[Sean_Jaymo 0]

Evening, I'm having a bit of mare with my electrics. There isn't really an electrical section on this forum, so I thought I would go for the ICE/Secure section as it is kinda electrical!

 

 

Bit of a broad outline. I'm running a 92 VR6 Corrado which I have fitted a 24v AUE lump into along with fitting a Teves20 ABS system. All were working well until I looked on VCDS the other night to check something on the abs system to find that my brake pedal was registering as ON permanently irregardless of pedal position. This was checked in measuring block 3 of the ABS channel. When I installed the TEVES20 system, this field would change correctly depending on the brake pedal position.

 

 

To confirm if it was the brake pedal switch or not, I looked in block 66 of the Engine ECU channel and found that it displayed 0001 with the pedal up or 0011 in field 2 with the pedal down. This proved that pins 2 and 3 of the switch were working. The switch itself is no older than 4 or 5 months and the car hasn't been driven.

 

 

The issue lies with pins 1 and 4 of the switch. Pin 1 gets its feed from E4 and when the switch is made, the current should run up Pin 1 and when the switch is made, it runs out of PIN 4 along to E3 and along to ECU pin 121/56. I have physically checked every mm of the wiring for faults and there are none.

 

 

When the IGN is OFF, Pin 4 shows as 0V, BUT when you switch the ignition system to RUN, it shows 12V. On the fusebox, the rest of the brake circuit runs through K4 and W4 where K4 is the feed from E3 to the actual brake lights and W4 is the feed to tell the ABS ECU Pin 12 that the brakes are on.

 

 

I disconnected the W and K plugs from the fusebox and the fault still shows, which indicates that the 12v feed is coming from ECU plug 56. I removed this pin from the ECU and run a dummy wire so that I could measure the voltage straight from ECU pin 56. It shows as 12v with the ignition on and 0v with the ignition off. A look at block 66 on VCDS shows 0001 in field 2. This shows that the brake light switch is ON. Earthing ECU pin 56 resets the reading to 0000.

 

 

To prove that brake light switch pins 1 and 4 should work as advertised, when the feed from the ECU is removed, you get 12v as advertised from fusebox pin E3 when the pedal is pressed. I'm confident that the switch is working correctly.

 

 

This is annoying in itself BUT!

 

 

Measuring the voltage through fusebox plug W4 shows 12v when the Ignition is on and 0v when it is off. This is another signal wire to tell the ABS ECU that the brake lights are on. It shouldn't show 12v from the ABS ECU! If you remove the 2 fuses it will still show 12v indicating that the ABS Pin 12 is getting its power from Fusebox pin D7 which is the signal wire to tell the ABS ECU that the car is switched on. You can get VCDS measuring block 3 to show brakes are off when you earth pin W4.

 

 

I would initially think that the ABS or engine ECU could be faulty but for both to show the same fault at the same time when both were working before hand is very confusing and I think there MUST be a link.

 

 

Recently I relocated the battery to the boot but I can't find any faults with that and I can't find any spare earths anywhere that I missed. Disconnecting or fitting the 2 TEVES20 ABS Loom earths doesn't make any difference to my readings. Neither system has its own dedicated earth in the circuit, they share the common earths in each ECU from what I can work out!

 

 

Please any guru's! Help me, I'm becoming increasingly frustrated! I like a challenge, but I have spent my entire day on it and got nowhere! Why are both ECU and ABS pins which are supposed to read voltage IN from the brake lights, showing 12v OUT??!

 

 

EDIT: To make matters worse, NO faults codes are logged at all! In Either system!

[Sean_Jaymo 0]

Any ideas?

[Sean_Jaymo 0]

Anyone?