VATS Bypass (97-02)
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VATS Bypass (97-02) The idea of a relay is an electrically operated switch. The TDR receives the signal from the ECM which closes the switch which allows the signal wire to the starter to be powered. When we bypass the BCM wire (yellow with black stripe), is this bypass simply powering the relay to stay in the locked position or connecting the circuit the relay is trying to close? Is it not easier to get a correct gauge wire to short it or even a correct amperage fuse to put in place of the relay circuit thus keeping it powered? Right now its really god damn cold out and I can't move the wiring harness much to do any splicing. I've resorted to starting the car via the purple wire on the passenger side via a jumper cable and the positive terminal. I have the VATS disabled in the tune so I will get fuel, just can't power the starter. No security light flashes, just can't start it via key initially. (I can start it via key AFTER doing the purple wire start, I think I get x number of failsafe starts before I have to pop the hood and redo)
After reading up on this all day, I think I've figured out that the TDR only exists in earlier VATS cars, the 97+ is built into the BCM. The yellow-black stripe wire goes from BCM to the starter relay in the engine bay. If the temps don't cooperate enough to allow me to bypass from the engine bay, I'll see about doing it from the BCM harness on the passenger side.
Any electricians in here to confirm this line of thought?
After reading up on this all day, I think I've figured out that the TDR only exists in earlier VATS cars, the 97+ is built into the BCM. The yellow-black stripe wire goes from BCM to the starter relay in the engine bay. If the temps don't cooperate enough to allow me to bypass from the engine bay, I'll see about doing it from the BCM harness on the passenger side.
Any electricians in here to confirm this line of thought?
Last edited by SladeX; Feb 19, 2019 at 01:50 PM.
Joined: Nov 2003
Posts: 11,330
Likes: 346
From: Jacksonville, FL (originally from Toronto Canada)
For 97-02 f-bodies, VATS is in the BCM and cannot be programmed out (the BCM is not programmable). It blocks starting in two ways - the BCM will not send a fuel enable signal to the PCM and it doesn't provide the needed ground for the starter relay coil. The PCM can be programmed to ignore the lack of a fuel enable signal but the starter relay must be rewired to bypass that part of the system. This is quite simple... just cut the yellow/black wire near the relay and run the relay end of the wire to a good chassis ground. No fuse is required (it's ground anyway so if it shorts to ground there would be no damage) and 18 gauge wire is sufficient since it's only the low current relay coil.
The disadvantage of doing it this way instead of the usual resistor bypass is that the security light will still be lit if the key pellet doesn't match (it will flash if there is no key pellet found). If your security light isn't currently on then VATS is probably not your problem. Have you checked that the starter relay is working? You can swap in one of the fan relays to see if that solves the problem.
The disadvantage of doing it this way instead of the usual resistor bypass is that the security light will still be lit if the key pellet doesn't match (it will flash if there is no key pellet found). If your security light isn't currently on then VATS is probably not your problem. Have you checked that the starter relay is working? You can swap in one of the fan relays to see if that solves the problem.
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I already replaced the relays (they are 20 years old!) and still the same problem. Grounding the yellow/black wire worked and I was able to start the car normally for once. No security light popping on, but sure does behave like the VATS system. I suspect something between the BCM and starter relay is my problem or the BCM itself, but I don't have the cold endurance to troubleshoot beyond what I can easily access. I already tuned it out with HP tuners and did the resistor pellet bypass years ago. I did the cold weld fix years ago when my windows/radio acted up and am wondering if this is potentially yet another cold weld issue with the BCM.
Joined: Nov 2003
Posts: 11,330
Likes: 346
From: Jacksonville, FL (originally from Toronto Canada)
The symptoms suggest that your suspicion of a problem with the wire between the starter relay and the BCM is the most likely cause - in which case replacing the ground there should have fixed it permanently. It is possible that there's another cold solder problem in the BCM but I've never heard of one that is specific to that circuit. The common one is the RAP circuit that you already fixed but if it broke again then you would experience radio and window cut out rather than anything VATS related. I would keep it in mind in case you experience starting problems again but for the moment I think you've fixed the problem.
