[T3] car died on way home

Jim Adney jadney at vwtype3.org
Sat Apr 7 20:40:26 PDT 2012

On 7 Apr 2012 at 16:53, Bryon Garvin wrote:

> Testing blue/white wire in plastic connector (back-probing method):  Got
> 12v with key turned, jumped to 14v when engine ran, back to 12v when engine
> died.

Okay, the 12 V supply side of the relay is fine. That means that it's 
getting its supply from the main power relay as it should.

> Testing white wire in plastic connector:  Got 12v when key turned, then
> this:
> 1st time: stayed at 12v while engine ran, when engine died, still showed 12v
> 2nd time: dropped to 5v while engine ran, when engine died, back up to 12v
> 3rd time: same as first

This side of the relay is not getting grounded properly, so the relay 
is probably fine. That wire is grounded by a transistor in the brain, 
but this will only work if the connection all the way back to the 
brain is intact. The problem could be the connection at the engine 
firewall, just to left of center, where the FI harness wire connects 
to the other end of that white wire, it could be a problem in the FI 
harness, or it could be the transistor inside the brain that is 
responsible for grounding this wire.

Check the firewall connection first. This is a 1 to 1 connector. Make 
sure the male plug is actually inserted INSIDE the female connector, 
not just alongside it.

If that connection is good, remove the connector from the brain and 
look in the opening. Turn the box so that the PC board is on the 
bottom with the connector slot facing you. On the right side, about 2-
3" in, there will be a metal case transistor with a heat sink on it. 
Push gently on the heat sink to see if the transistor will move 
easily sideways in any direction. Just gently. It will feel stiff in 
all directions if all 3 legs are intact.

It could also be a problem internal to the transistor, but there's no 
easy way for you to check that. I would have to send you another 
brain to try to see if that fixes it.

My first bet is on the firewall connection. I've seen a transistor 
with a leg rusted off, but that was in a very humid environment.

> Hand on fuel relay under back seat confirms that it clicks off only when
> the key is turned off.

Good, that's as it should be.

Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA

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