Mechanic’s Tale: Theft Deterrence

Mechanic’s Tale: The Big Cat by Douglas Flint (8/21/2006)
I fell in love with a machine — and lost.

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The advent of cheap electronics in the late Seventies, combined with an ever-increasing auto theft problem, led to the growth of a large aftermarket industry manufacturing and installing automotive antitheft systems. While it may not have been a problem in the wheat fields of Kansas where people could probably still leave their keys in the ignition switch, the situation on both coasts was quite out of control, further aggravated by police forces and politicians who viewed auto theft as a social condition akin to unemployment.

These aftermarket systems, usually installed by the guys who put new radios in your car, were certainly better than nothing, but were only capable of defeating the most amateurish of thieves (which fortunately was often good enough). After all, the only thing the antitheft system could do was to interrupt power to either the starter or the ignition system, both easily bypass-able. They could make a lot of noise, but in New York City , who’s going to notice?

The system that impressed me as having the best chance of working allowed the car to start and run a half minute before shutting off in the middle of an intersection with sirens blaring and lights flashing, leaving the embarrassed thief with little choice but to huff it away. Many new-car dealers began offering aftermarket antitheft systems along with the undercoating and upgraded stereos they had been making so much money on for years.

The chip in the key

Two things happened to take antitheft to the next level. The manufacturers noticed people wanted and were willing to pay for, or at least assign value to, antitheft systems. The rise of electronic engine controls meant some pretty formidable antitheft systems could be built into the car fairly cheaply. GM had one of the earliest widely available systems starting in about 1990. The ignition key itself had a chip on it with a certain electrical value. When the key is placed in the ignition switch and turned, a magnetic pick-up coil reads the key and sends the data to a security module. If you’ve used the correct key, the security module communicates with the engine control module and allows the car to crank and start. If not, the car will not engage the starter to crank and, even if you run power to the starter, the car will crank but not start as the engine control computer will not allow spark or fuel.

The system has been on millions of cars for over a decade and has proved quite reliable. The only problem I have observed is that once in a while, the little wires in the ignition switch that connect the pick-up coil will become brittle and break, but the repair is fairly easy, requiring no special tools or electronics. And if the system has a problem, the security light will come on and the engine control computer will store a fault code, making for easy diagnostics.

One wonders why they would change such a system. But they did.

Suburban nightmare

One of my regular customers complained of an intermittent “no start” on her '99 Chevy Suburban. She brought it in numerous times, but all our diagnostics revealed nothing, and the vehicle failed to cooperate, starting perfectly every time I was near it. But gradually I got more information. When it wouldn’t start the starter would crank but the engine would refuse to fire up. Typically this happened after her morning run of child drop-offs and shopping. She would park in her driveway, come out an hour later, and that’s when it would occur.

Still I was unable to duplicate it, but she had some other drivability issues that matched the profile of a GM tech bulletin concerning a bad crankshaft position sensor. The crankshaft position sensor is the sensor that tells the computer that the engine is turning and how fast (engine speed), and is the single biggest cause of problems on almost all cars and trucks. So I replaced it. No luck. She only lived a mile from the shop so I told her next time the problem occurred call me and I would try to get out while the problem was occurring. Several times I made the trip but each time I got there it started.

Finally I witnessed the problem and observed fuel pressure was ten pounds under spec and would drop to zero immediately when it turned off instead of maintaining pressure for a period of time as it should. Confident I had it nailed, I replaced the pump. But two weeks later the problem occurred again. It stayed in its mode long enough for me to notice that it would actually start momentarily then die out. I verified good spark, good fuel pressure, yet it seemed to start then run out of fuel. (I have a good ear and a fuel-injected engine makes certain noises when running out of fuel.)

Unfortunately I couldn’t prove it because by the time my mechanic got back with a can of carburetor cleaner, which we use to manually feed the engine, it was starting and running on its own. Nonetheless, I was convinced something was shutting fuel off at the injectors. I hadn’t considered antitheft because the key had no chip in it and no fault codes were stored in the computer. But there was a security light on the dash, so the vehicle did indeed have antitheft. And I learned it would indeed allow the vehicle to start momentarily, then cut it off by clipping the fuel injector circuit.

A call to Identifix put me in touch with a technician who explained what he could about the system. Its operation was similar to the system with the chip in the key, but instead, the ignition switch itself had the coded electrical value. Befuddled, I asked how this would prevent someone from jamming a screwdriver or other tool into the lock cylinder and forcing it to turn, since it contained the antitheft code. The tech I spoke to said he’d wondered that too, but GM had assured him it wouldn’t work.

Since I have the GM Tech 2 scanner I was able to access the antitheft module on the Suburban which, unfortunately, had no failure codes, nor would it be likely to, since the memory of an incorrect voltage code would only last less than a minute. But the truck had some other issues that needed work, so I convinced the customer to let me keep it and drive it a couple of days. With my Tech 2 scanner by my side I was convinced I would catch it in the act.

Mistake!

Having the Tech 2 by my side wasn’t good enough. It acted up the very first morning I went to start it, but in my confused state at 7:30 a.m., by the time I got the scanner plugged in and programmed the car started. So for the rest of the time I had it, I kept the scanner plugged in and made sure I was tuned into the antitheft module before trying to start. Unfortunately, over the next three days and 53 recorded starts it failed to act up.

I’m fairly convinced the problem is in the switch assembly, but I have replaced a crank sensor and a fuel pump, needed or not. I don’t feel I can be wrong again. Meanwhile my friend Joe has been wrestling with similar problems on a Ford with antitheft – also to no avail. So in spite of the right tools and good knowledge, neither of us has solved his customer’s problem. This does not bode well for the future.

In my mother-in-law’s new Infiniti, direct contact with the key is no longer necessary to start the car – just wave it around or have it in your pocket and the car detects its presence. You can turn the ignition switch and start the car without the key. I can only imagine the havoc such a system could cause when it’s ten years old and feeling a little cranky.

So here comes one of my pleas to the manufacturers. Please make your antitheft systems as bulletproof and failsafe as you can. Don’t withhold the software and testing info under the guise of proprietary software. And at least make sure that if the antitheft system prevents a start, it sends a nice firm fault code to the engine control computer that we mechanics can actually retrieve, so we don’t spend hours barking up the wrong tree, only to tell our (and your) customer that they have to take it back to the dealer for a computer reflash.

A good antitheft system leaves the customer feeling secure. The thief should be the only one feeling exasperated.

Doug Flint owns and operates Tune-Up Technology, a garage in Alexandria, Va.