I just got in from the garage, I need to get this off my chest.
The timing marks could be better.
"That mark should be about at that screw, that one about that screw, dum-dum-dumty-dum, what's paralax?" These things like to skip time, and it could be so much easier to set it. The factory attitude seems to be take it all apart, get a new chain, line it all up fresh. I can't get a clear view of the pulley timing marks in my Xtrail. I can see them, but in reality there is a whole lotta paralax error, easily a tooth's worth. There should be two marks on the case. Sure, you can try and line it up with the bolt centerline, but there's a big wide shiny socket on that. With two marks you could at least know whether or not your reading is trustworthy. Or you could line up a ruler.
Solution: Dial indicator TDC. The cam marks are still just as bad; vague single points of reference, prone to paralax error. I found the valve timing diagram from the FSM and put a dial indicator on the tappet, and I think I found a better way:
Turn the crank over to the next TDC. Now the mating mark on the exhaust sprocket (or is it a gear?) is next to the Intake sprocket. The mating mark tooth should line up to the closest tooth on the intake sprocket at precise TDC.
Then you can count Iinks between the sprocket marks. 14 links when there's a marked tooth inside 1 and 14. 13 if the marked teeth are in between links. Make sure you have tension on the chain for this. If your tensioner is pinned, I would pull it tight with a clamp behind the chain guide and be confident in your timing before pulling the pin. Always tension the crank and intake cam (24 mm spanner between cyl#1&2) in opposite directions for readings.
If the timing is off, it can be set from above. Mark your chain for where the tooth needs to be beforehand. Once the tension is off, everythings a mess, jumping everywhere, no measurements hold true. Mark it beforehand to where it needs to be set. The oil tensioner needs to come off (DON'T DROP IT INTO THE CRANKCASE, NOoooo!!!...) The cam sprockets need be loosened and pulled out a bit, but just undo the bolts enough that the sprocket pops out to hang on top of the bolt. If you pull out the bolt, oil runs out of the cam. It's messy, and also not ideal for the next start up. Your cam bearings get air instead of oil.
If your cam and crank pos sensors are too much off, it won't start. It'll give you one round of sparks as hope, then nothing. And you won't get a clear code, oh no, the computer says no go but won't tell you why. Not with a generic reader or the engine light flashing read out. The factory diagnosis involves a two channel oscilloscope, but it can be confirmed with a multimeter, breaker bar, marker, and tape or cardboard. The hall senosors will give you a reading when a)powered b)under constant rotation. By hand is fast enough, just semi-constant in the normal direction of rotation. You draw as you observe, then do the other sensor next to it. Compare to a healthy example, just like with an oscilloscope.
I'll go to bed now. The subject deserves a clearer post with pictures, but I need to get this down fresh.