: How to bypass the VATS (Passkey II) system for a mid 1990s Cadillac

06-12-09, 10:15 PM
This article was found on the web but has been customized for mid 1990s Cadillacs with the Passkey II system
1991-1996 Fleetwood
1992-1997(?) Seville SLS/STS/Deville
Before we begin, here's a question to consider:

When you insert your ignition key and attempt to start the car, will the car not even attempt to crank over? Does the "Theft Deterrent” message appear in the display and then a message saying “wait 3 minutes”? Most likely the VATS (Vehicle Anti Theft System) reader in the ignition is worn out. You can still review the trouble codes while the car is disabled – hopefully you already know how to do that. Turn the key to “on” and enter the diagnostics mode. Look for codes B2710, B2711 or B2750 to be displayed which is a good indication the passkey was not properly detected.
Note: there is a possibility the VATS module is at fault and this bypass procedure will not solve that problem.

There are 3 things you can try first (hopefully you are not stranded). Try starting car after each step:

Clean the key’s resistor “pellet” which is the silver line in the black insert near the end of the key with a clean pencil eraser or fine steel wool (both sides).

Clean the VATS “reader” which is the two contacts just inside the ignition key hole. Use a bit of isopropyl alcohol on a Q-tip and clean just inside key hole to remove any dirt that might be on the contact(s) preventing a connection to the resistor pellet. Inspect the Q-tip, and if dirty, repeat until clean.

This is a last resort. A locksmith suggested with a small piece of spring-steel that you put a very small 90 degree bend on it near the end and try to pull backwards on each contact just inside the keyhole. Put a small bend towards the center of the keyhole on each contact which should put more pressure on the pellet. He said 9 out of 10 times this won’t work – and in my case it didn’t work either.

At some point we all make tough economic decisions concerning our car repairs. A dealer could charge as much as $600 to replace the ignition key tumbler and VATS reader. I got a quote from a locksmith who would do it for around $400. This involves removing the steering wheel and turn signal to gain access. Another option is to bypass the VATS reader costing you about $12 for parts from Radio Shack.

**NOTE** after performing the following procedure, your Cadillac’s factory starter interrupter (VATS) will be disabled. A thief will be able to steal your car much easier than if the VATS system were enabled.

How does the VATS System work?

Each VATS key has its own unique cuts on the key to operate the lock. The cuts alone will not allow the car to crank. This is called a mechanical key. Each car has a VATS module (Brain) under the dash that communicates to the starter, fuel pump, and the ignition lock. Each VATS module is randomly given a number (see VATS # below) from the manufacturer. When the proper mechanical keys, along with the proper VATS “pellet” (embedded resistor) turns the ignition lock, the VATS module reads the pellet on the key. If it is the correct pellet, the VATS module will tell the starter, fuel pump and injectors to operate. If the wrong pellet is read or the correct pellet can’t be detected, the VATS module will tell those components to shut down and display a theft deterrent enabled message.

How to determine the Value of your key:

You might already know what VATS key belongs to your car, but most people don’t. There are basically two ways to determine what VATS key you have. Remember, there are 15 different possibilities. First, your key can be "read" in a VATS tester. Most locksmiths have these testers or at least a Volt Ohm Meter (VOM), and don’t charge anything to read your value. There is another way for you to read the key value yourself. If you have your own Volt Ohm Meter you can test the Ohms (resistance value) of the pellet. Just set your Volt meter to check OHMS (20k ohm setting) and take each probe and place it on each side of the pellet on your key. A number will appear. Take that number on your volt meter and apply it to the VATS # / OHMS chart below. Keep in mind that it may not be exact. Just pick the closest value to your reading.

This chart is for any GM product, Buick, Cadillac, Oldsmobile, Chevrolet, and Pontiac that has a VATS key (single or double-sided.)

VATS # OHMS(k) (Set your meter to the 20k ohm setting)

1———— 0.402
2———— 0.523
3———— 0.681

Tools and supplies needed:

Soldering Iron
Wire Cutters/Strippers/Crimper
Voltmeter/Ohmmeter (VOM)
Approx. 8 inches of 16 gauge wire (speaker wire or some old wire from a lamp should also work)
"Bullet-Style" solderless connectors (optional, if you want to reverse this in the future)
Heat Shrink Tubing
Resistors of varying values (totaling the resistance measured across the key's "pellet")


1. Write the resistance value (Ohms in k value) down on some scratch paper. Leave room for calculations as the total resistance by resistor type will need to be figured out in the store.
2. Go to an electronics store and purchase a resistor or resistors that add up to the value you or a locksmith measured. Radio Shack is a great place to go for the resistors, heat shrink tubing, and the "bullet-style" solderless connectors. Be prepared to do some “on the fly” math though as resistors come in odd values. Also make sure all the resistors are the ½ watt rating as it’s easy to gather different wattages by mistake. Sometimes the wrong resistors are in the drawers so make sure to double check the package.
3. Take the 16 gauge wire and cut into 2 four-inch pieces.
4. Strip off approx 1/4" of insulation off each side of both wire pieces.
5. Put your resistors together in series starting with the highest value(s) to the left and string them so the lowest value(s) is to the right. Make several twists as you join the resistors. If you're lucky and have a pellet that has a resistance that matches a single resistor, you just attach the wires to each end of it. Now flux and solder one wire to one end of the resistor(s) and the other wire to the other side. Complete the job by fluxing and soldering each twisted joint between each resistor.

Example: You measure 11.72 on the 20k (k meaning kilo or 1,000) scale. The closest match is 11.801 which is a #15 "pellet." Always remember that resistors have a tolerance of 2%, meaning the resistance value of the "pellet" can be either 2% higher or 2% lower than 11.801 k ohms (11.72 falls in tolerance range.) You will want to aim for 11,801 ohms. So when you go to Radio Shack you want to pick up a 10,000 ohm (10k,) a 1,000 ohm (1k,) and an 800 ohm resistor to wire together in series to achieve the 11.801k ohm value. Keep in mind that the wattage rating on each resistor must be the same (1/2 watt).

Here's an example of how you'd connect the above mentioned resistors in "series". Start with the highest value on the left and work your way to the smallest value to the right:

wire------10k ohm------I------1k ohm------I------800 ohm------wire

6. Measure the resistance across the 2 wires now that the resistors are soldered to them. Be absolutely sure the value matches that of the resistor pellet in the ignition key (within 2% up or down.)
7. Cut a length of heat-shrink tubing to cover up the resistors, allowing a small bit to hang over onto each of the 2 wires. Use a lighter or heat gun to shrink the tubing.
8. On one of the wires, crimp on a male bullet connector, and on the other wire crimp on a female bullet connector. OPTIONAL: if you decide you want to solder the resistor chain directly to the VATS wires, skip this step.
9. Now what you have should look something like this:
Notice in the above "resistor pack" only one resistor was needed to match the pellet's resistance. You may not be so lucky...
10. Now move to the car. Remove the under-dash kick panel on the driver’s side.
11. Look for an orange plastic straw-like conduit running down the steering column. It should be by itself and not bundled with other wires. Near the end of it where it joins a large harness, look for two grayish-white wires coming out and going into a clip on a corner of the large harness.

**WARNING** Do not tamper with any of the wires near the column wrapped in yellow harness tape or any yellow wire. These wires are for the airbag. Tampering with any of these wires could result in the airbag discharging.

12. Cut this conduit with the 2 grayish-white wires inside allowing about 3 inches, if possible from the large harness to work with. You can now pull off the orange conduit on the harness side. Strip back the insulation on the wires on the opposite side of the steering column (harness side) for about ¼ inch. Do this carefully as the wire has very fine strands. Tip: cut two 1 inch segments of the heat shrink tubing and slip one over each of the grayish-white wires. This will allow you to optionally solder the leads instead of using bullet-style connectors, and then later, slide the heat-shrink tubing over the soldered joint. NOTE: If you choose to solder, this offers the best and most permanent resistor circuit for the VATS module, but is not as easily reversed. Also, you will be soldering under the dash, so if this poses a challenge to you, then go with the bullet-style connectors and crimp them on.
13. Now twist the stripped wire from the resistor pack to the stripped wire of the grayish-white wire. Then do the same for the other set of wires to form a “loop” Insure the twisted connections are good. Take a key and test the starter. It should start and run. Now you know you have the correct configuration to bypass the VATS reader. If this didn’t work, recheck the total resistance of the chain and be sure both the twisted leads were tight for the test.
If the test still won’t start the car, you most likely have a problem with the VATS module. Remove the resistor pack. Strip the insulation off the other side of the main wire cut (running from the column) and place a male connector on one wire and a female on the other. Now place a male connector to one wire on the harness side and a female connector to the other. Plug the 2 halves back together to restore the function of the VATS reader.

Steps 14 and 15 assume your test worked:

14. If you decide to go with the connectors, install and crimp a male bullet connector to one of the 2 grayish-white wires, and a female on the other. Now do the same for the resistor pack. Plug in the "resistor pack" that you made by mating the male and female bullet connectors. See diagram.
15. If you decide to solder for the best connection, flux and solder the twisted connections you made for the test, and after cool, slide the one inch heat tube over the joints. This will prevent possible shorts – heat the tubing to shrink. Now tuck the entire loop up above the other grouped wires and replace kick panel.

06-23-09, 05:30 PM
Thanks I will try this. One question I have is, can the resistors be connected together with the solderless connectors. I want to use the solderless connectors first to see if it will work, if it does I will go back and solder everything. Thanks.

06-25-09, 07:24 PM
I would suggest putting several "twists" to conjoin the resistors. You want a good connection in the string to assure the test goes right. Remember - highest values first to successively lower values from left to right. Once it tests good, solder the string.

04-10-16, 11:18 PM
I've been stranded and I tried this. It didn't work. :cry: I have no dtc codes nor does the security light light up. The battery is fully charged as well. I could only find 1/4 watt resistors, will this make a difference? I have also was within 1 ohm of the specified resistance. It's 1991 deville base model.

04-11-16, 07:41 AM
Old dead thread dredging are we....
1/4 watt more than enough.
Post your issues with exact symptoms (no crank, no start, etc) with fixes attempted.
Those resistor will need to be soldered together and to the wiring.

04-11-16, 08:23 AM
There may be more info in the Deville or Electrical or Security forums, too.