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AUTO Q AND A: Troubleshooting a GM Pass-Key/VATS problem

Question: I have a 1998 Olds 88 Delta LS. I am experiencing intermittent no-starts. The dash lights come on but the engine is silent and won't start. This no-start situation has been occurring at random intervals of a few weeks at a time. I've di...

Question: I have a 1998 Olds 88 Delta LS. I am experiencing intermittent no-starts. The dash lights come on but the engine is silent and won't start. This no-start situation has been occurring at random intervals of a few weeks at a time. I've discovered that if I merely watch the LED time clock display and wait for 3 minutes, the engine will turn over perfectly. I took it to a dealer who said that something was corrupted in the computer, and that replacing the computer would be expensive and there was no guarantee that whatever caused the corruption initially wouldn't cause it again in the new computer. What could cause this?

Answer: Your Olds, like many GM vehicles of this vintage employs Pass-Key II (previously called Pass-Key or VATS), a sometimes troublesome theft deterrent system. The ignition key contains a visible black resistor pellet that is read by contacts within the ignition switch as the key is inserted. If the correct resistance is seen, the theft deterrent module sends a command to the theft deterrent relay, allowing starter operation, and a more sophisticated signal to the powertrain control module (PCM), which authorizes fuel injector operation. If an incorrect key is used (or the key is misread due to faulty contacts) the system denies these functions for three minutes. There are 15 possible key values, so should a thief obtain a copy of your key (the physical cut but not the pellet) or was to bust the ignition switch, many minutes would likely pass before a compatible key/pellet or electrical sneakiness was successfully attempted.

This system differs from more sophisticated imbedded chip/radio signal key systems, as the keys are inexpensive, and a key learning procedure (for replacement keys) is unnecessary. The down side is the ignition switch 'reader' contacts have proven to be less than robust, causing intermittent no-starts, and a diligent thief can eventually prevail, armed with an assortment of properly cut keys or resistors.

Here's a friendly recommendation for all GM Pass-Key/VATS owners: measure and record the resistance of your ignition key pellet! This is a 10 second job using a simple ohmmeter (depending on the pellet, it will be somewhere between 402-11,800 ohms). Once you obtain the resistance value, Yahoo or Google "VATS key codes". You'll quickly find a listing of the GM pellet resistance/key chart, which will tell you which key (#1-15) you have. You can then purchase appropriate spare key blanks on ebay for as little as $5 apiece or buy/have additional keys cut locally at a heads-up hardware store or locksmith.

Now, to your problem: I believe the ignition switch is occasionally failing to read the key properly. Begin by measuring the key and taking a trip to Radio Shack to buy a 1/2 watt resistor of the same value (less than $1). If necessary, securely twist/solder several resistors together, end to end, to obtain the specified value (+/-5%) and tape-up/insulate all but the two ends. Next, remove the hush panel beneath the steering column and locate the Pass-Key ignition switch connector (contains two slender wires, about a foot down the column from the steering wheel). Unplug the connector and insert the ends of your resistor(s) into the connector leading to the instrument panel. The theft deterrent module will now think the correct key is inserted. If the engine now starts every time, you need a new ignition switch (about $50), or secure the resistors in place and be done with the problem (and antitheft protection) for good. If the occasional 3-minute starting lockout still occurs, the theft deterrent module or related wiring is at fault. If needed, a used/recycled module ($20-50) can be employed, if you have the patience to learn its key code, and a handful of resistors.

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