P0686 and P0687 codes - Saab 9-3SS Bulletin Board - Saabnet.com
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07 9-3SC 2T 168K miles
About two months ago I had an MIL come on which, on reading, showed a P0638 code (throttle positioning). Car ran fine, although it did start VERY rough once the day before the light came on. I was due for a major service in about a month and the car seemed OK, so I left it. Took it in to the former Saab dealer for the service, asked them to pull codes and advise. Tech2 showed a P1682 (plausibility fault between +15 and main relay) and the P0638. Recommended replacing the main relay, but the technician noted that often this didn't completely solve the problem and many cars had required the engine wiring harness to be replaced. But the harness is NLA from Saab although they had located a used harness. So I had them replace the relay (least expensive thing first).
Car ran fine for 10 days, then set a P0687 (ECM power relay control high). I cleared it, then it set again a day later, then 4 days later set a P0686 (ECM power relay control low), then 2 days later set a P0687 again. Today I had 3 p0686s and a P0687.
Searching here and on other sites, causes people found were engine wiring problems, bad ECM, and problems with the AC fans. The AC runs cold when no codes are set. Today was the first relatively warm day (80F) we've had, so it seems to be heat related (which may point to an ECM). But I also have set the light a couple times after a quick stop for a traffic light change (which may point to wiring).
Thoughts on what to do next? I love the car and would like to keep it 2 - 3 years longer (until the selection of electric vehicles expands) but would prefer not to go down a rabbit hole of throwing parts at it. I'm also wary of a used harness, which at best would be 10 years old. Any thoughts about that?
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