From Mike Bigus(gtivr6r@chicagonet.net)

O.K. here we go, lets take it one step at a time.

Bentley Repair Manual page 24a-5

Note: The Motronic systems are equiped with built-in fault diagnostics.  Some of the faults will illuminate the check engine light, but many will not.

Bentley Repair Manual page 24a-6

TO DISPLAY DTCs (Diagnostic Trouble Codes)

1. With the ignition key ON *(see addendum below), use a jumper wire or the OBD adapter to connect terminal 4(ground) to terminal 15(L-wire) for 2.5 SECONDS and remove the jumper wire or adapter.  See drawing below (1994 and later).
   Caution: Use care when connecting the jumper wire.  Positive (+) battery voltage is present in the connector.  A wrong connection can result in damage to ECM (Engine Control Module) or the vehicle's wiring.

2. After (1) one blink of the check engine light, the first 4-digit DTC will be displayed.  Approximately one second later, the check engine light will blink the first digit, the npause, blink the second digit, then pause and so on.
   Note: A blink code of 4-4-4-4 indicates that NO malfunctions have been stored in permanent memory.

3. Once the first DTC has been displayed, reconnect the jumper wire or the adapter for 2.5 SECONDS and then remove it.  The second DTC code (if present) will be displayed.

4. Repeat step 3 until no more codes are displayed. (DTC 4-4-4-4 displayed)
   Note: The 4-4-4-4 code will be represented by four long blinks.

5. Turn the ignition key OFF. Erase the DTC codes once all testing and repairs have been made.

Bently Repair Manual page 24a-5

Note: On 1996 models cars, a specaial OBD adapter is stored under the back seat and should be used to access the DTCs.

To Erase DTC Memory

1. With iginition key OFF, connect the jumper wire or the adapter to the diagnostoc connector.

2. Turn key ON, wait at least 5 SECONDS and then disconnect the wire or the adapter.

3. Reconnect the jumper wire or adpater for 2.5 SECONDS and then remove it.  The first DTC codes (if present) will be displayed.

4. Repeat step 3 untill no more codes are displayed. (DTC 4-4-4-4 displayed).
   Note: The 4-4-4-4 code will be prepresented by four long blinks.

5. Reconnect the jumper wire or adapter for 2.5 SECONDS and remove it. The DTC memory is now erased.  Turn iginition key OFF.
   Note: To confirm the memory has been erased, repeat step 3.  There should be only a 4-4-4-4 code (four long continuous blinks) present.

"With the ignition key ON, use a jumper wire or the OBD..."

to

"With the engine running, use a jumper wire or the OBD..."

Here's my long winded explanation:)
My '93 Corrado (VR6) ECU blinks out a DTC for a faulty engine speed sensor (2111) if the engine is not running when I connect the jumper wire. This is normal. There is nothing wrong with my speed sensor. If the engine is running I just get the 4 flash end sequence.

Neither Bentley or the CCA Garage Tips tells you to blink out codes with the engine running. If you don't know this and you follow Bentley's trouble shooting guide for a faulty engine speed sensor, you may wind up replacing a perfectly good sensor or worse yet trying to fix the engine speed gear (that's bolted to the crank).

I owe many thanks (and probably many hours) to Todd at Air & Water VW Tuning in Philadelphia who sent me the following (I e-mailed him based on an earlier list server posting of his):

I dug the following posting of yours out of the archives. Thanks for submitting it. Did you ever get the engine speed sensor problem resolved on your '93 Corrado?

Uh, yes... I finally figured out that the speed sensor code will always appear when the engine is off/key on. Start the engine, and the code should erase.

Todd
Air & Water
VW Tuning
Philadelphia

Thanks for maintaining a great site! Your garage tips and other pages have saved me countless hours (Almost as many as I've spent browsing the site!!)

Andy Ellis
'93 Corrado
Madison, Wisconsin

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