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1985 Sedan DeVille
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Discussion Starter #1
The service engine soon light on my 1985 SDV activates whenever I heavily accelerate, but turns off again when I let off. Sometimes it will flicker at cruise speeds with no acceleration too, but that is not very common.

Is there a way to pull diagnostics for this lamp? I've got the factory service manual, but I don't see a way to pull these specific diags.

Thanks
 

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White Diamond '03 DHS (with DTS floor shift)
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86,990 Posts
Try simultaneously pressing and holding the OFF & WARMER buttons. Should be in the FSM. If not in the diagnostics section, maybe the HVAC section. Been a long time since I had an '85 manual.
 

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1985 Sedan DeVille
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Discussion Starter #3
I got the car back from the mechanic and redid the tests--I was looking at the wrong panel last time DOH

E26 and E52 come up in the history before 7.0.0. The E52 may be from changing the battery ("reset"?). E26 looks real, since the OFF indicator stays lit on the climate control panel, which is supposed to indicate that the throttle is open.

I don't know why E26 would sporadically trip the Service Soon light though. Maybe its too rich due to throttle sensor problem, and goosing it may cause an environment sensor to trip then clear (although I'd expect it to be in the history).

Yesterday I went up to the big city and back in ~90 degree weather with full oil and coolant. The light did not come on going up, but it did flicker on and off coming back. It lost a little oil (just a little) and the coolant level dropped a couple of inches (may have been too high). Running the tests just now it sounds perfect at idle, but almost sounds like it is missing during acceleration. Also noticed that it was VERY slow off the line after traffic light changes. Time for a new sensor and a fuel injector/line cleaning I think.
 

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1985 Sedan DeVille
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Discussion Starter #4
Follow-up here, I had it in the engine shop this week and the mechanic said my problem is a busted sensor in the idle speed control motor. They are replacing the whole assembly while they do a overall tune-up. Looks like my engine is in pretty good shape overall.
 
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