Hey folks, just thought I would run a quick problem by you.
Just my luck, I am soon going for our provincial etest for my 1990 420sel, and im having an odd issue with my check engine light.

Only from a cold start, when I start the car, I get a 7 blink code from the engine light, which indicates "TNA-signal (RPM-signal) read by CIS-E implausible"
Any other time I start the car within the day I get no engine light at all and no codes. FYI this is not a California car.

I built the diagnostic led/switch harness, however on my car, pin 3 on X92 under the hood has no connector (no metal sleeve inside), and thus no way to read the code "as per the mb instructions" via this diag port, and no way to reset the code. Like I mentioned above, the engine light on the dash is blinking this code to me, only when the car is first started for the day, it does not re-appear or come on again any other time during the day.

The car runs fine, no issues at all, and the tach works as always. SO this leads me to believe something odd is up. Seeing that this car has only one CPS to read the rpm info from, if the tach is working as expected, and theres no sputtering/misfiring.. What else can the CIS be cranky about?
Car starts right up, and within 2-3 seconds, settles down to 500-600rpm.


Today im going to take the car out for a spirited spin and double check my duty cycle and such, just to make sure everything is working as expected, then off to testing D-day!
Honesty, etesting is like the most dreadful thing for car guys.. I absolutely hate it, ob2 versions no problem, but the sniff test on these older cars, you have no ideal if you will pass.

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Just my MB's:
1990 420sel - Winter DD - 410,000km
1990 560sel - absolutely showroom mint - 360,000km!