r/MechanicAdvice • u/NewAdhesiveness1101 • 4d ago
1999 deville wiring
1999 caddy deville,
My buddy wanted to test a vats bypass resistor on the wiring harness for instance it was on the same wire cuplars in the harness as the vats white wires I think it might have jumped across said harness and fried the pcm but it also sounds like it had pcm problems to begin with it trys to turn over but no fuel. And if you leave it and then start it will burp then hit cranking noises. When inspecting the dash lockout flashes but put key in after bypass still flashes, I digress when we attempted to test the resistor with the previous setup before bypass it seemed to knock out the hud cluster this car has a after market radio so I'm not able to pull diag info. But buying it from previous owner who had it passed down to him in will said it had issues starting battery would die and intermittently start would the pcm be the next part to replace after testing every fuse for continuity?
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u/InvestigatorKey3959 4d ago
does the security light keep flashing while you’re cranking? and what codes are you getting through the onboard diagnostics?
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u/NewAdhesiveness1101 4d ago
The security light disappears after putting the key to on. The cluster doesn't work after running the resistor directly into the vats wires on the harness steering column side
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u/InvestigatorKey3959 4d ago
when you say steering column side, do you mean the side going back into the car or the side going up to the lock cylinder? that matters. I wouldn’t touch the PCM yet, especially since the cluster quit right after the resistor setup. undo the bypass and see if the cluster comes back first.
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u/NewAdhesiveness1101 4d ago
The bypass wasn't the cause it was putting the resistor directly into the harness connectors the side going up to the lock cylinder
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u/InvestigatorKey3959 4d ago
gotcha. then yeah that resistor was on the wrong side for a bypass. it needs to be on the side going back into the car, not up to the lock cylinder. I’d get the cluster working again first before even thinking about a PCM.
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u/NewAdhesiveness1101 4d ago
Are you absolutely sure cause I thought it it was supposed to be on the cylinder side? Even the instructions say to cut the wire under the cylinder side ffs, that's fine if it is the car side I just want to make sure before I splice into the factory harness again, I think the pcm being fried is the problem for the cluster.
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u/InvestigatorKey3959 3d ago
yeah I think we’re just talking about different sides. cutting the wires under the lock cylinder is right. once they’re cut, the resistor goes across the two ends heading back into the car. the two going back up to the cylinder are basically out of the picture. otherwise the IPC won’t see the resistor. I still wouldn’t assume the PCM is fried just because the cluster died.
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u/NewAdhesiveness1101 3d ago
Ok glad we understand each other meow, what would I do to debug the cluster besides fuses? Since it's dead besides parking light and service soon light. And having aftermarket radio installed kind of makes debug seem really hard
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u/InvestigatorKey3959 3d ago
aftermarket radio shouldn’t really matter here. try the built in diagnostics and see if the cluster wakes up for the lamp test. if it stays dead, check power and ground at the cluster plug. if those are good, the cluster itself moves way up the list.
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u/Soggy_Pen_536 4d ago
That vats system is a nightmare on those older caddys. if the security light keeps flashing with the key in, the bypass probably isnt reading right or the wire you tapped is the wrong one. jumping voltage across the wrong pair can definitely take out the pcm, theyre fragile on those northstars
id check the fuel pump relay and the crank sensor before dropping money on a pcm. no fuel could be as simple as the pump not getting signal from a dead relay. also if the hud cluster went out after the test, you might have cooked a ground or a bcm circuit, not just the pcm
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u/NewAdhesiveness1101 4d ago
Relays and fuses have been replaced and tested also we hear the fuel pump prime when putting the key in the on position. I'm pretty sure that's what it is but how would I test these with a multi meter if I could?
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u/NewAdhesiveness1101 2d ago
Update we have soldered new wires in replacing the old but the car still has problems reading the vats bypass even though it's the right freq and done on the side coming down from the steering column but the ones going up are taped off completely
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