2001 S40- Just happened...CEL and flashing arrow. Did the 'shift from P-D 20 times' routine, the arrow went out, but the CEL Remains. I can't get to a code reader until Monday (It's Friday). Any ideas? No change in tranny feel, car rides just fine. Can I drive 20 miles?

2001 S40...130K...My CEL went on...had it checked for codes...700/705...PNP switch. He turned off the CEL, I drove it about 50 miles and it returned. I ordered the new part. Had the CEL turned off...it's been about 100+ miles, the CEL has not returned !!! Do I change the PNP, or assume that the unit is working fine? If I get another 50+ miles and still no CEL...does that confirm my decision? The part was $100...the labor, I can do...except it seems to get a tad hairy with the adjustment phase of the install...Otherwise I would not hesitate to install it... Ahhhh....what to do, what to do.

If the PNP is bad it will return. Bet you a cup of coffee!

Replacing it is not as bad as you think. One of the positioning shortcuts is to put the car in R with the key on. The PNP also acts as the backup light switch. If the lights do not come on, adjust the position again.

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My back feels better when I sit in a Volvo seat

Drive it and the CEL may go out on its own after "x" amount of run cycles and "x" number of miles.
I would be more concerned if the CEL was flashing. Then you should get it read sooner than later.
Be aware though, resetting CELs on that vintage S40 can be a challenge.
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"Differences of opinions should be tolerated, but not if they're too different' - Sharon Craig

You did good, go ahead and drive it.

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My back feels better when I sit in a Volvo seat