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2001 GMC Jimmy Crank Sensor Bypass Test...

posted Jul 05, 2016 13:34:36 by EdCurry
Ok here's the deal, I have an 01 Jimmy I just did an oil pan, timing cover and valve cover gaskets on. Car cranks but no start; popping a p0335. Unplugged crank sensor; I have 12 volts, ground and a signal (sort of). When I do a bypass test on the signal wire (test light connected to battery +) coil fires. Although, when I do the same test with my power probe, WITHOUT pressing the 12 volts button, the coil fires and air pump kick on. I traced the signal wire back to the computer and did the same test, same results. Is this a bad pcm? I was hoping to find the wire rubbing on ground but I don't see anything.
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3 replies
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EdCurry said Jul 05, 2016 14:10:05
update: computer does respond when manually bypassing sensor; when it's plugged in no rpm signal when cranking.
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Noah said Jul 08, 2016 12:51:36
Any way you can scope the signal wire while cranking?
Massachusetts, USA
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RobBrown said Jul 08, 2016 18:08:22
Have you verified a lack of spark when the truck is a crank/no start? If you aren't seeing any spark, and you then DO get spark with the bypass test (with evidence of a good power and ground feed on the harness side of the CKP connector, it's almost certainly a bad crank sensor ("almost certainly" because I suppose there's a very slim chance that it could be an engine mechanical issue causing the engine not to produce a crank signal). The bypass test (along with testing for presence of power and ground) verifies that everything north of the sensor itself is good to go.
[Last edited Jul 08, 2016 18:10:08]
Just a dude who found a sudden and unexpected passion to bless folks who can't afford auto repair with free help. I never, ever imagined this is how'd I'd be spending my free time:-)
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