The P1646 mystery

After a recent hard driving session I got MIL and a P1646. No restricted performance, nothing noticeable changed. Also if you deleted the code it would not illuminate again until next startup.

All good and well, not the first time I get a trouble code.

Things got a little more hairy when I opened my X308 workshop manual to troubleshoot the code and found that the P1646 is a secondary fuel pump relay issue, pertinent only to the supercharged version. Mine is the non-supercharged 4.0 V8, I don’t believe I have a secondary pump. So, what’s happening here?

I’ve red reports of the same code being used as a pass side upstream O2 sensor, but no mention of that in my manual. Is the info reliable? Don’t want to be forking out for a new sensor, let alone going through the pain of removing old one etc. if the one I got is good.

Here’s proof:

what year is your car ?

It is two thousand and one

P1646_X308.pdf (162.7 KB)

Maybe try a normal BROWN relay in the socket?
If the fault does not recur, then call it GOOD?

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Sorry, I don’t follow. Try a brown relay in which socket?

The socket slot that the #2 fuel pump relay would normally go if the car was SuperCharged.

Thats an interesting idea. I’d try it but if it worked it would confuse me even more!

Can’t help you with strange electrical faults over the internet but electronics have no answers at times! Maybe the harnesses have a ‘queertron’ infection?

Haha. Nah, not a big believer in magical thinking me.

i suspect this is the upstream exhaust sensor (with grey plug)

HO2 Sensor Control Malfunction Bank 1 Upstream