04 XC90 t6 tach jumping no start

KevinCro · Post by **KevinCro** » 20 Jul 2020, 19:05

Hey guys. I got the used engine swapped into my XC90. I’ll say this first. Never buy a broken down XC90 just to have something to tinker with. That being said, the engine will crank but won’t start. The tachometer jumps up and down and it’s throwing a p336 crankshaft position sensor circuit code. I have made sure all the bolts were in the bell housing. I had a new sensor that I had already bought for the old engine so I swapped that in, And added a ground strap from the starter bolt to the frame. None of this made any difference. Any ideas?

Post by **SuperHerman** » 21 Jul 2020, 23:27

Well your code says you have a crank shaft sensor issue. A failed unit will cause a non-start.

I would track the harness back - look for a compromised wire/harness/junction. Not sure if there is a fuse. If you have a VOM you can use that to help.

Any information on the vehicle before you bought it (other than a bad engine)?

KevinCro · Post by **KevinCro** » 24 Jul 2020, 09:54

Fixed!! I replaced the starter and she fired right up. Hope this helps someone in the future.

Post by **SuperHerman** » 25 Jul 2020, 00:03

Thanks for the follow up and I am glad you got it sorted out. I am puzzled on how you got the code for crank position sensor which is strange. Did you clear the codes before starting the process or could the old code be one that was lingering? Is the code gone now? What scanner did you use? Did you clear the code?

How did you figure on the starter? Was it not spinning fast enough? You have my curiosity peaked.

It would be good to keep the crank position sensor in the back of your mind in the event you get a non-start in the future. I have not seen a bad starter display ANY code on any Volvo I have worked on.

KevinCro · Post by **KevinCro** » 25 Jul 2020, 00:19

Well I have a scanner from harbor freight. I’m nit sure if you are familiar with that store or not but it’s nothing fancy. The engine never turned over, even with the old engine, the way I thought it ought to, but since this is the first Volvo I’ve ever owned I didn’t have a reference point to compare it to. I do know that I had never seen the tach jump like that before I installed the new engine. This was even more puzzling since the starter was the same as before. The only thing that was different was the wiring harness had been between the block and the starter originally, but when I put it back together I had put the starter on before hooking up the harness so now the harness was on the outside of the starter. When I scanned the car for codes I got a crank sensor fault and nothing else. Prior to installing the new engine I was getting cam sensor codes so I new that something had happened during the install to cause this fault. After some research on “tach jumping no start” I saw several forums where people were blaming the starter. I thought this was ridiculous at first but nothing else helped. I gambled and replaced the starter and it worked. I suppose it was any port in the storm and I stumbled upon the right port.

KevinCro · Post by **KevinCro** » 25 Jul 2020, 00:25

The crankshaft sensor operates on a magnetic pulse and apparently when a starter is breaking down it draws a heavy current load. This makes sense because my brand new battery would die much quicker than it should trying to get the engine to start. The current draw, as I understand it, interferes with the magnetic pulse which in turn confuses the computer.