VATS/Security light
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Staging Lane
Joined: Feb 2016
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VATS/Security light I know this has been covered ad nauseam, but I have a little twitch that I am wondering if anyone has run into. 2002 Z28, Security light on, no crank, no fuel pump running. I have the GM pinpoint tests.....there is 5v on the fuel trigger line from the PCM, and the proper key resistance at the BCM (it has a VATS bypass installed by previous owner). Pinpoint test says BCM is bad. Now.....while I don't have HPT or EFILive, I do have Tunerpro RT. I was able to turn off the VATS flag and reflash the PCM, which allowed the fuel pump to run.....but no crank. As per GM's wiring diagrams, the starter relay is grounded through the BCM; my guess is that if the BCM is not happy it will not close the ground to the starter relay regardless of how the PCM is tuned.....unless there is a parameter that shoots data back to the BCM telling it to close the starter relay ground. I haven't gone as far as jumping the relay coil to ground yet as I ran out of daylight. Has anyone come across this?
Launching!
Joined: Nov 2015
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If I'm reading the schematic correctly, the PCM doesn't appear to affect the BCM operation. It's the other way around, the BCM effects the operation of the PCM by providing it with a ground path input which allows the PCM to enable the fuel supply. The same solid state board in the BCM also controls the ground path to the starter relay coil. If this board was faulty and unable to provide that path, there appears to be no other way for the starter relay coil to receive a ground allowing it to energize, without physically rewiring to the relay socket on the under hood fuse block to a different ground source. If you think about it, the purpose of this system is to deter theft by making it a complicated and a time consuming process to bypass starting the car without the proper key. While it is not foolproof, it does what it is designed for.
I just finished looking through more drawings and found where there is a starter enable signal from the PCM to the BCM. That said, if the BCM solid state board was bad, the contact allowing the ground to the starter relay coil may not be operational. Anyway you can confirm the PCM signal being sent to the BCM?
I just finished looking through more drawings and found where there is a starter enable signal from the PCM to the BCM. That said, if the BCM solid state board was bad, the contact allowing the ground to the starter relay coil may not be operational. Anyway you can confirm the PCM signal being sent to the BCM?
Last edited by peterpar; Dec 13, 2019 at 04:37 PM.
Thread Starter
Staging Lane
Joined: Feb 2016
Posts: 70
Likes: 6
I just finished looking through more drawings and found where there is a starter enable signal from the PCM to the BCM. That said, if the BCM solid state board was bad, the contact allowing the ground to the starter relay coil may not be operational. Anyway you can confirm the PCM signal being sent to the BCM?
Launching!
Joined: Nov 2015
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That signal is actually the fuel enable signal, and it's a +5v supply from the PCM. My understanding is when the BCM is satisfied that the proper key is inserted, the BCM will ground that circuit 50 or 60 times per second (depending on vehicle), telling the PCM to enable the fuel pump and injectors. I did indeed test that wire for voltage, and it registered +5v like it should....yet I was still getting the P1626.
Joined: Nov 2003
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From: Jacksonville, FL (originally from Toronto Canada)
I suspect you guys are getting into it far too deeply. The described symptoms indicate a VATS condition of not recognizing the resistance of the "key" (bypass resistors). This is entirely normal operation for that condition - the security light is illuminated, the fuel enable signal to the PCM is disabled and the ground for the starter relay is also disabled. It is unlikely that there is anything wrong with the BCM. Your options are to fix the bypass so that the BCM "sees" the correct key resistance value again or work around the VATS functions - you've already programmed it out of the PCM so all you have to do is ground the yellow/black wire at the starter relay. As mentioned, the security light will still be illuminated but you can block that with a piece of electrical tape or disable it by cutting the gray wire in position C12 of the blue 32-pin connector at the BCM (there are two gray wires... you want the one next to the yellow/black starter relay control wire).
Launching!
Joined: Nov 2015
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