sierrafery
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The key learning for me was that there is a separate switch inside the XYZ switch body which immobilises the starter unless the gearbox is in P/N. Do not assume that just because the gearbox selector lights/in dash gear position display correctly show P, that the separate starter immobiliser switch will be in the correct position.
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Hi... you have a good point and thanks for sharing your experience with this cos it's a really intersting issue... the oddity is that the P/N output from the XYZ switch to the BCU and all others(IP, ECM, etc) comes out on a single wire which splits between all and goes to C0663-11 BCU too and that's the only P/N input for it.
IMO there is only one switch for P/N output, my theory is that the switch's alignment must be perfect as all the XYWZ contacts within it to be in correct position... once earth goes out on the P/N output wire from the switch(C0675 - 5) the contact must be tight cos even if the signal's strenght is enough to light up the indication it's not strong enough for the starter relay coil's management too due to reverse voltage drop also all the other contacts must bbe in the perfect position to not be other unneeded output too which can mix up things... i'm not 100% convinced that i'm right but that's what i can think based on the diagram
but i completely agree with your last statement:
DO NOT ASSUME like I did that because the P indicator was lit up on the gear shift / in the dash display,then the starter inhibitor logic built into the BCU will be OK !!!
i pointed red arrows to the the P/N signal output/input from XYZ to BCU to sustain my theory:
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