Vehicle Anti-Theft System (VATS)
As you may already know, some of the TPI systems were used on vehicles on which GM implemented a security feature known as VATS. It stands for Vehicle Anti-Theft System. When first introduced by GM on the 1988 Corvette, vehicle theft was reported to have dropped by 30%. This was a simple, and effective system in its time. However, it is an annoying feature when trying to install TPI on a vehicle that does not have a VATS system installed.
How It Works
The idea behind it is very simple. The ignition key has a "chip" (just a resistor) installed on it, which can be easily seen. When you attempt to turn the ignition ON, the resistance of the chip is measured, and compared to the value stored in the VATS decoder module. If they are the same, a signal is sent to the ECM telling it to fire the injectors (pin F10 for the 1227730 ECM, and pin B6 for the 1227165 ECM). At the same time, the starter enable relay will be energized by the VATS decoder module. If the wrong resistance is read, then the signal will not be sent to the ECM, the starter enable relay will not be energized, and the injectors will not fire. Additionally, a code 46 will be shown. This code will not be stored in the ECM's memory, and is only present while the conditions for a code 46 are present. The module will shut down for 2 to 4 minutes. During this time, any attempts to start the vehicle will not work. If the ignition switch is turned during this time, the timer will restart even if a key with the correct resistance is used.
There are 15 possible resistance values that were used by GM.
402 ohms (acceptable range 386-438)
523 ohms (acceptable range 502-564)
681 ohms (acceptable range 650-728)
887 ohms (acceptable range 850-942)
1130 ohms (acceptable range 1085-1195)
1470 ohms (acceptable range 1411-1549)
1870 ohms (acceptable range 1795-1965)
2370 ohms (acceptable range 2275-2485)
3010 ohms (acceptable range 2890-3150)
3740 ohms (acceptable range 3590-3910)
4750 ohms (acceptable range 4560-4960)
6040 ohms (acceptable range 5798-6302)
7500 ohms (acceptable range 7200-7820)
9530 ohms (acceptable range 9149-9931)
11800 ohms (acceptable range 11328-12292)
What It Was Used On
The contents of the PROM is what decides whether or not the ECM is expecting a signal from a VATS decoder module. Some proms have it enabled, some have them disabled. The PROMS that have it enabled can be reprogrammed to disable VATS. If you would like to know if VATS is going to be a problem for your TPI install, the following will be helpful. The information below is broken down by ECM number.
1227730 and 1227727
All factory PROMS had VATS enabled. If you are installing TPI on a vehicle that already has a VATS system installed (like a 1990 Camaro RS for example), then you do not need to disable VATS from the PROM. If you are using a Speed Density computer on a vehicle that does not have a VATS system installed (most applications) then you will need to have VATS disabled in the PROM. If you need this service performed on your PROM, contact us for more details.
All the factory PROMs used on 1989 models had VATS enabled. In addition, the 1988 Corvettes, and most 1988 Trans Ams had VATS enabled. If you are installing TPI on a vehicle that already has a VATS system installed (like a 1990 Camaro RS for example), then you do not need to disable VATS from the PROM. The only time you will need to disable VATS is if your PROM came from one of the models mentioned above, and you do not have a VATS system in your vehicle. If you need this service performed on your PROM, contact us for more details.
If your prom came from anything other than the models mentioned above, then it does not have VATS enabled. In this case, you can run your PROM without any modifications.
None of the models which used this ECM had VATS enabled.