Steve’s 1993 Cadillac Allante Theft System Fix

“Ohhhh the relief when the key turned.”

That is how Steve opened his message to us, and by the time you have read what came before it you will understand why.

A friend of his had bought a 1993 Cadillac Allante. Shortly afterwards it stopped starting. Some days yes, some days no, and then never. A shop kept it for eight months and could not fix it. The dealer declined to work on it at all.

“I was the last chance in a line of failure.“

The false start

Steve’s first theory was reasonable: an aftermarket alarm had been fitted, so that was the obvious culprit.

“I uninstalled the alarm with no issue, quickly put in the key and to my dismay, nothing…. No crank, then it appeared.. A readout on the hardly readable display that came in 3 separate all CAPS waves, ‘REMOVE IGNITION KEY’, ‘DUE TO THEFT SYSTEM’, ‘STARTING DISABLED’. It was at this time my heart sank. I had promised I could get the car started and it was not looking good.”

He tried the resistor trick. It failed.

“I tried the resistor trick, where one wires in a matching resistor the key… ahh ha, that’s got to be it….. nope…. No crank, no nothing except for a ‘THEFT SYSTEM ARMED’ light in the dash and the 3 above mentioned display readouts.”

This is a competent technician doing the thing every forum recommends, correctly, and getting nowhere. Worth remembering next time somebody tells you a resistor is all it takes.

One second of victory

He kept going, through wiring diagrams and forum threads, and found the starter bypass relay:

“I grounded the signal and bam, the motor cranked, the car fired and shut off nearly immediately…and again, that readout of failure flashed across the diagnosis screen, as it had done before. I was so close. but yet so far.”

Then he found the wall that stops everybody:

“It was at this time I found out about the fuel cutoff circuit and that without some serious engineering, I would never get past it…. I almost through in the towel, with my friend encouraging me, ‘Come on man, you can do it’.”

That is the crux of these systems and Steve worked it out from first principles. Defeating the crank is achievable with a jumper. Defeating the fuel side is not, because the security module is telling the engine controller not to run. You can make the starter turn all day and the car will still die a second later.

Thirty minutes

“I studied over the very simple instructions, flipped the dip switches, connected the 4 wires and then it happened…. I turned the key and like nothing had ever happened, the car started…. not only did it start… it ran… and ran with no errors no issues… in disbelief, my friend shut the car off, turned the key again, and it fired even faster.“

“If you ask me, had I to do it again, what would I do…. I’d say without a doubt, order this module and be done in the less than 30 minutes it took me to install, of which most was removing panels to get to the harness I needed in the car. It’s worth far more than it’s sold for. You’ll see when you get it, it’s not some simple resistor in a black box, but far more… this is a miniature computer that is quality built with a simple install process and most of all WORKS.”

Steve P.

Why the Allante is its own problem

The Allante uses a PassKey Decoder Module, and on the 1992 and 1993 cars it lives on a board with several other components under the left side of the dash. It reads the resistor pellet in the key and, if it disagrees, it disables both the crank and the fuel.

That two-sided lockout is exactly why Steve’s careful, methodical work got him a one second start and no further. There was nothing left to diagnose. The system had to come out of the decision.

If you have an Allante

Three guides cover the run, by module location:

• 1992 to 1993 Allante, PDM under the left side of the dash. This is Steve’s car.
• 1989 to 1991 Allante, PDM behind the right side of the dash.
• 1986 to 1988 Allante, where the PDM is unplugged and left unplugged. The bypass replaces it outright.

If your car is showing that same three-part display message, you are not chasing an electrical gremlin. Identify your system here before you spend another weekend on it.

The NEWROCKIES PRO Module covers this failure across the GM range, and the full vehicle list is on the home page.

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