Alh brake switch question

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cursingvw

Member
Joined
Aug 28, 2016
Location
mn
TDI
2002 jetta
So i got my alh running in the 98 4runner but as soon as i touch the pedal it goes WOT. there is no brake switch hooked up as i thought i didnt need it. On VCDS pedal is always 65% then at full pedal it jumps to 85. Doesnt read anything in-between. I'm thinking i need the brake switch but i think there are other gremlins behind this.

Also is the brake switch wired directly to the ecu or is there a relay in there?
 
jimbote

jimbote

Certified Volkswagen Nut
Joined
Jul 10, 2006
Location
spiral arm, milky way (aka central NC)
TDI
Tacoma 4x4 converted to TDI
how did you wire the throttle pedal? did you cut out the plenum connector and splice the wires directly? have you tried a different pedal? Brake switch would NEVER cause it to behave as you describe.
 
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C

cursingvw

Member
Joined
Aug 28, 2016
Location
mn
TDI
2002 jetta
jimbote said:
how did you wire the throttle pedal? did you cut out the plenum connector and splice the wires directly? have you tried a different pedal? Brake switch would NEVER cause it to behave as you describe.
Click to expand...

I just shortened the wires after the blue T10 connector.

I haven't tried another pedal yet. I suppose i will have to.

Is there any way I can totally bypass the brake switch without a tune? I guess i thought i could just delete it but now ive learned otherwise.
 
C

cursingvw

Member
Joined
Aug 28, 2016
Location
mn
TDI
2002 jetta
The donor car pulled the old runaway diesel and i thought it was due to a leaking turbo but perhaps it was the pedal?
 
jimbote

jimbote

Certified Volkswagen Nut
Joined
Jul 10, 2006
Location
spiral arm, milky way (aka central NC)
TDI
Tacoma 4x4 converted to TDI
cursingvw said:
I just shortened the wires after the blue T10 connector.

I haven't tried another pedal yet. I suppose i will have to.

Is there any way I can totally bypass the brake switch without a tune? I guess i thought i could just delete it but now ive learned otherwise.
Click to expand...
there is a way to bypass the brake switch, again not the issue. When you shortened the throttle wires did you match color for color or pin for pin? The reason i ask is because as the wires pass through the plenum connector the colors on one side do not carry through to the other side. In other words if you cut out the connector and wired color to color at least two pair are incorrectly matched. Unplug the throttle pedal and see what happens in vcds.
 
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cursingvw

Member
Joined
Aug 28, 2016
Location
mn
TDI
2002 jetta
Yup everything was carefully done. blue connector is still there i just shortened the pedal side

Ill give unplugging it a try tonight.

I believe you the brake switch is not the problem but i will have to address this to get throttle response in the end.
 
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C

cursingvw

Member
Joined
Aug 28, 2016
Location
mn
TDI
2002 jetta
Im wondering if the pedal is shot because the donor car floated exhaust valves into pistons. I had assumed it was runaway diesel but perhaps pedal failed and then it somehow caused it to keep reving even with everything shut off. IDK. Thoughts?
 
H

HoneyBadger

Veteran Member
Joined
Dec 25, 2012
Location
San Jose, CA
TDI
'02 Jetta 5 spd, 03 jetta auto, future ALH Ranger
I can't comment about the pedal, but it would certainly be possible for it to fail into requesting full throttle and wreck the motor.

With the pedal unplugged, the engine should idle a little higher than the usual ~900 RPM. I can't remember the number off the top of my head, but it's around 1200 or so.

It sounds like your pedal might be bad if all the wiring is all good. Also do what Jimbote says and check VCDS.
 
C

cursingvw

Member
Joined
Aug 28, 2016
Location
mn
TDI
2002 jetta
Well i ran out of time this evening. Doing 10's don't leave a lot of time around normal activities. Hopefully tomorrow i can run VCDS. What exactly am i looking for without the pedal hooked up?

It was idling fine until i would touch the pedal then she would go until shut off.
 
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cursingvw

Member
Joined
Aug 28, 2016
Location
mn
TDI
2002 jetta
As soon as the pedal was disconnected it went to 0% so i guess I'll be ordering a pedal.
how should i bypass the brake switch?
 
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