DME / ECU testing questions

[LateFan]

In the Bentley tests for the DME pins, are you connecting your multimeter to the cable / harness side of the connector, or to the pins on the DME case?

And if the DME is unplugged, what would it matter if the ignition is on or off? How are signals getting through the system?

I'm a bit confused in the electrical world.

[jlevie]

How to do this depends on what you are testing. In some cases the tests can be made with the DME disconnected. Other tests must be done with connector back shell removed, the DME connected, and the ignition on. A check of the CPS signal (with an oscilloscope) must be done like the latter case, but with the engine running.

[LateFan]

Oh, so you can get to the pins while it's still connected? I haven't had it apart yet.

[nando]

there's a cover on the harness plug that you can remove. should be a Phillips screw, maybe two. haven't looked at an M20 plug in a while.

[LateFan]

Thanks!

[TobyB]

What helps a lot is that the pin numbers are on the mating face of the vehicle connector.
So if you're checking things like flapper door resistance, you can meter right there.
If you need voltages, you can find the pin, then meter through the back with the connector
back on the ECU.
The first time you take that connector apart, it's a bit terrifying- these harnesses weren't
built any better than they had to be, and stuff's just packed in there any way it'd go.
On top of that, your harness will self- disassemble to some degree, so have friction tape
or hockey stick tape or something else you like to bundle it all back up again.

Better than a Saab, but nothing like the E21 or 2002 harnesses...

t