Porsche 944 turbo DME diagnostics
TEST socket fault codes and idle adjustment
(944Turbo only)
The DME/KLR computer puts out a morse-code type blink signal at the test socket that may be used to diagnose problems with the wastegate-controlling cycling-valve, the knock-sensor operation, and throttle-position sensor. The test socket is located on the firewall just ahead of the fusebox. You can flip up the plastic cover plate and it should look like the picture.
Instead of buying the official Porsche diagnostic tool that plugs into this socket, you can use a simple LED, low wattage bulb (less than 2w) or a needle type multimeter to extract the blink codes. Use the two terminals labelled LED and + in the picture. The rotation of the socket may be different, so you can orient yourself by finding the C terminal that's off by itself. Connect the negative lead to the LED terminal, and the positive lead to the + terminal. The negative lead on the LED is the shorter one that's next to the flat spot on the casing. The positive lead is the longer one.
VERIFYING CORRECT LED ORIENTATION
You can check that you've got the LED hooked up right by disconnecting
the throttle-position sensor with the car idling. If the LED goes on,
then it's hooked up correctly.
GETTING THE BLINK CODES
The fault code is
lost when you turn off the ignition so if you�ve had a problem don�t
turn it off before checking for fault
Go out for a short drive and run it through the rev-ranges. Try small
and full throttle openings. Then bring it back and with the car idling,
hook up the LED and check the blink-codes. If you have a problem that it
knows about, you should get a group of blinks, a short pause and another
group of blinks, then a long pause and the cycle repeats again. Or you
may get more than one error code.
IDLE ADJUSTMENT
When you adjust the idle speed you must disconnect the idle actuator otherwise it will keep adjusting the idle rpm. To do this connect a wire between terminals B and C of the test socket. You should notice the rpm change. Now turn the idle adjustment screw until the correct rpm is achieved, you should notice it is much easier to alter now without the idle actuator working.