Thread: Won't turn over. Suspect P and N switch

Originally Posted by shack

I'm thinking that a failed XYZ switch will cause the BCU to prevent cranking as it doesn't detect it in park or neutral?

Interesting that the indicators on the selector quadrant work but not the odo one. Does the BCU control both? I imagine so, but I don't know. But my suspicions, amateur as they are, lean toward a BCU issue. As sf says, test this in the Nano.

This has been a timely thread, as I have been experiencing intermittent non crank issues myself recently. As usual, AULRO is a good teacher.

Originally Posted by Tins;[URL="tel:3228411"

3228411[/URL]]Hmm.. Might test that. Might also put the transfer case into neutral first..

So that’s a yes. Car will crank in any selected position if set to manual.

Originally Posted by shack

I'm thinking that a failed XYZ switch will cause the BCU to prevent cranking as it doesn't detect it in park or neutral?

If I'm correct, you can set the BCU to manual gearbox and it will crank again.

I'm pretty sure that's correct, but please correct me if not!

I did a LOT of Diag getting the Auto to run standalone without defaulting, and that was one of the tests I did from memory.

But as above, please let me know if that's incorrect...

You are not incorrect.... the only comment i have is that as long as the BCU receives the "park" input(in this particular case confirmed by the selector assy display albeit the LCD doesnt show selection) the starter is not inhibited, a failed XYZ switch would not let it crank only if it doesnt deliver the correct outputs hence my advice to check them with nanocom

Life intervened and I was unable to do any work on the car for a few days.

Today I set the BCU to manual gearbox with transfer case in Neutral. No change in Nanocom display. (Sometimes neutral in the transfer case is hard to engage so I wouldn't know if it was really in Neutral.)On another setting the Nanocom did not recognise Neutral in the TC.

I removed the R2relay and bridged the contacts. Tried every combination as not sure what "perpendicular" meant. Three horizontal pins and one vertical. No clicks, sounds, anything. Relay in or out made no diff.

With Nanocom I went to BCU-Read Inputs-Body2 and XYZ all seemed to give the ON message at the right time. Outputs body- crank enable ........could not find that.

I did find that the Nanocom thought it was a petrol/ manual, so I put it right.

At the moment it's on charge to keep the battery up.

Jiggled the starter cables. Seemed sound. Battery terminals and cables look clean and no crud.

Originally Posted by Tinggu

1. I removed the R2relay and bridged the contacts. Tried every combination as not sure what "perpendicular" meant. Three horizontal pins and one vertical. No clicks, sounds, anything. Relay in or out made no diff.

2. With Nanocom I went to BCU-Read Inputs-Body2 and XYZ all seemed to give the ON message at the right time. Outputs body- crank enable ........could not find that.

1. You should have asked for clarification before bridging cavities all around cos it's not healthy at all to bridge the coil's circuit with live, perpendicular are the two which would make a T between them, where the relay's contact goes, 30 - 87 in the pic

2. my bad, crank enable is in "outputs security" 2'nd page ...though that's futile if the starter doesnt kick in with relay's contact bridged connect somehow a wire to the starter' solenoids terminal(where the thin wire with spade connector goes) and give it direct live...if no activity it's the starter, if it cranks that way and fusible link FL12 is not blown replace that fusebox or open it and find the crack if you know how

Good luck

With all the other historical electrical issues you have mentioned, I'd be focusing on the IDM/Fusebox under the dash, instrument cluster and ignition switch itself for correct operation.

This is assuming you have checked the basics such as having power ( or not ) to the pigtail (small lead) on the starter while in the crank position?. If yes, then starter solenoid is a likely culprit

Originally Posted by Tinggu

No clicks, sounds, anything. Relay in or out made no diff.


Jiggled the starter cables. Seemed sound. Battery terminals and cables look clean and no crud.

Seems to me like it's either the cables to the starter or the starter itself, if you bridged 30/87 on the relay socket. That should energise the starter no matter what else is wrong. So, when you jiggled the wires at the starter, and the big cable was secure, last resort would be to make a jumper wire, connect it to the small terminal on the starter and touch it to the Batt +ve. This will eliminate pretty much anything else, such as BCM and XYZ switch. If you get nothing then it's most likely the starter, or a bad connection on the main batt terminal at the starter, or a bad earth.

I'm having a parallel issue, where mine wants to start as soon as I turn the key to II. Only way I can get it to stop this is to pull relay #2.

Bloody pic is upside down.... sigh... Might be worth checking the security of the two screw terminals I've pointed at as well. Careful, they are Batt +ve.
Screenshot 2024-07-03 at 8.20.27 AM.jpg

Running again! I was going to run a hot wire from the battery to the starter but turned the ignition just for a laugh and she fired up as though it was a normal thing to do.
So I still have no idea what the problem is/was, or whether it will happen again. I don't have great faith in it right now.
Thank you all for your advice and suggestions. Without you people I would have had no idea what or how to check.
If it happens again I will show it a length of wire and a pair of pliers and see if that fixes it again.