Okay, here's how I checked for trouble codes:
1. Put the ignition in the "on" position (With the engine not running)
2. Find the diagnostic port just in front of the battery. it has a small lid and inside there are a bunch or numbered pins.
3. Take a small piece of wire and ground the #3 pin to the chassis for 2-4 seconds.
4. Remove the wire. In a couple of seconds the red LED will start to blink.
5. Count the number of blinks.
6. Lookup in the service manual (or google) for the cross-reference table that tells you what error message is correlated with the number of blinks.
7. You can also reset the check-engine light by grounding the #3 pin for several seconds.

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89 300te 222,222
92 300e 190,000