Ram Cruise and OD problems caused by Aftermarket Alarm Systems

Visit Geno's Garage
for Truck accessories.
Geno's Garage Truck Accessories


One of our Los Angeles Tech Advisors, Steve Doty was asked to look at a Ram Truck after a tech had spent three hours working on the problem. The truck arrived at the dealership with "no overdrive and speed control inop". The tech asked Steve to look at the speed control data recording. The problem was an obvious one if you know what the PCM must see before it will give you overdrive and the speed control.

Steve asked the tech to hook up the DRB and look at the PCM inputs/outputs to see if there was a change to Neutral/Drive when shifting the transmission. There was no change and it stays in Park/Neutral and won't start in Drive.

The next question," Does the vehicle have an aftermarket alarm? The answer was yes". Next Steve removed the starter relay and had the tech repeat the same test and then the DRB shows the change between Neutral and Drive.

The cause was the aftermarket alarm interrupt. These aftermarket systems insert a relay in the yellow wire coming from the steering column. When the key is on with the aftermarket systems there is 3-5 volt draw on the sense wire going to the Trans/Neutral switch. The PCM sees the voltage draw and thinks the trans is in Park and there is no need for Speed Control or fourth gear Overdrive. Steve tells us he has seen numerous examples of this situation with other aftermarket brands. This system was a Code Alarm and others that have created similar problems are Alpine and Prolock.

To demonstrate to this tech that this was the problem, Steve removed the starter relay and had the tech drive the vehicle. The speed control and overdrive both were working. Please remember that conditions caused by aftermarket installations and equipment are not reimbursable within the provisions of the warranty.


Last Update: October 15, 1999