2007 Uplander LT. Started van yesterday morning and it is driving very erratically. Like the engine is bogging down and is loosing power. Drove for about 50 km and parked, to do some shopping. Started and check engine light came on. It drove normal. Went to my small town garage and had it checked with their reader and it came back with " crankshaft position sensor" and " knock sensor". Why does it drive normal, after driving it, shutting it off, let it sit for 30 minutes and restart?

 

When the crankshaft position sensor fails it will typically fail when the engine is hot and only allow you to restart after letting it cool down and usually it won't restart when it is hot. When they are failing they will work ok cold -it likely has something to do with the electrical resistance of the unit changing with its temperature.

As a guess I would say that the crankshaft position sensor needs to be replaced and the code for the knock sensor was set when the crankshaft position sensor failed to a "limp home" state thus causing your poor running. They work erratically before they fail completely - this is pretty common on GM V6 engines. The knock sensor is likely OK.

Good Luck...

 

Thanks, 442dude,it was like you said. Had the crankshaft sensor replaced, at greater cost then I thought. Apparently the old sensor broke off during removal and they had to drop the oil pan, to hammer it out from the inside. $600.00 later, everything seems fine. Drove about 500 km and no problems. Thanks again.

 

Glad I could help and that you're running good again...but of course bummed it cost you $600. All the best!