change oil now light

VMM stuff

Oil Change Indication

The VMM monitors engine oil temperature and engine tachometer signals to measure quality of oil and indicate when engine oil should be changed.

The green bar under OK on the oil change display is lit for 0 to 89% of the oil change cycle, the word SOON under the word CHANGE is lit for 90 to 99%, the word NOW is lit for 100 to 115%, the word NOW is lit and flashes for 17 seconds when the ignition switch is turned on after 115% of the oil change cycle.

The oil change display will turn off after 15 minutes if the VMM receives no tachometer signal. This is a diagnostic precaution that could be caused by an intermittent connection or by the engine not being on.

After changing oil, the VMM must be manually reset:

1. Turn ignition to OFF position.

2. Turn ignition to RUN position, do not start.

3. Within 16 seconds of turning ignition to run, depress reset switch through the access hole.

4. The oil change display will flash, depress reset switch until the display stops flashing.
 
In addition: in 1990 there was a Technical Service Bulletin relating to the VMM. Apparently if the VMM was not reset every time the oil was changed, it would eventually produce a premature reading, about half of what the oil's actual life was. Some ppl have experienced this problem. You can check the TSB for 1990 in the New SC Owners forum. Perhaps the dealer can fix this freely for ppl with the problem.
 
The VMM actually reads mileage. After it is reset, when 3500 miles is run, it will go back to telling you NOW.
 
Its memory gets shorter with time.. When new, it flashes at you at the factory recommended 5000 mile interval. But over time, that inverval shortens to around 1300 miles. I just reset it and keep a yellow sticky with the oil change mileage next to the speedo.

I don't know what all it uses to determine this, but I think its fairly simple. Engine RPM over time would make sense because then it could roughly figure out how much oil was churned. If there's an oil temp sensor, I wouldn't know where it is.

If someone has a shop manual with a good electrical diagram and could solve the myster for us, it would be appreciated. Most manuals are lacking.
 
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