Jack’s 1995 Impala SS: Two Security Systems, Neither Trustworthy

Jack Rankin’s 1995 Impala SS, written up for us in May 2015, had a problem we have now seen enough times to call a pattern: a factory theft system going bad, with a decades-old aftermarket alarm layered on top of it, both wired into the same starting circuit.

Mainly a miss

“My 95 Impala SS was hit or miss on cranking over when I turned the key, mainly a miss. Sometimes it would start up then die 2-3 seconds later. Most times, it would not crank with no indication as to why.”

“I had a 20 year old aftermarket car alarm that was able to interrupt the starter as well as the OEM theft deterrent system. I wouldn’t drive the care anywhere, just out and about on the roads and straight back into the garage. You couldn’t trust it to start, ever.”

Note what the car had become: a garage ornament with an engine. An Impala SS, one of the great sleeper sedans GM ever built, restricted to laps around the neighbourhood because two separate security systems each held a veto over the starter and neither could be trusted with it.

Both problems out in one visit

“I decided to remove the old aftermarket alarm and install the new Pro-Module while the Technician was under the dash. All he did was set the dip switches and replace the OEM theft deterrent module and it started right up. Doesn’t get much easier than that.”

That sequencing is the lesson. We saw the same thing on Desiree’s 1992 Toronado, where a dead remote start was spliced through the column harness: when an old aftermarket system is in the car, it comes out first, in the same session, while the dash is already open. Installing around it means wiring into somebody else’s twenty-year-old work, and any fault afterwards becomes impossible to attribute.

What the factory side was doing

The 1994 to 1996 Impala SS, Caprice and Roadmaster run VATS PassKey: a resistor pellet in the key, read by contacts in the lock cylinder, judged by the Theft Deterrent Module above the brake pedal. Twenty years of wear make the reading intermittent, and the TDM answers an intermittent reading by blocking the starter, sometimes by killing the engine seconds after it catches. Hit or miss, mainly a miss, is that arithmetic seen from the driver’s seat.

The NEWROCKIES PRO Module replaces the TDM outright. With the old alarm gone in the same visit, the starter answered to exactly one thing again: the key.

If you have one of these cars

The wiring for the whole B-body family is here: 1994-1996 Chevrolet Caprice, Impala, Buick Roadmaster installation guide. And if you find an old alarm or remote start under the dash while you are in there, take it out before the module goes in. If you are not sure what you are looking at, stop and ask us first.

Related stories on the blog. The other dead-aftermarket-alarm case: Desiree’s Toronado, where a failed remote start was spliced through the column.

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