Traction Control

Dear Roy, The vehicle is a 1997 Lincoln Continental, engine VIN V, with a 4.6L DOHC engine, automatic transmission and traction control. I'm having a problem with the Series Throttle Control system. First a little history: The car was in previously, sporting a code P1220. After an extensive round of testing, it was determined the car had a faulty Series Throttle Controller. We replaced the controller, the telltale light on the dash went out and the traction control worked like a charm.

That is, until today. The car was once again presented to us with the telltale light and code P1220. The difference now is that upon initial key-on, the throttle plates are closing as part of the power-up test. This was not happening the first time around, and it is why the controller was replaced.

After another round of testing the stepper motor resistance, VPWR, signal return, TP-B voltages, grounds, etc., no problems were found. What I did find odd was that during the power-up test, the throttle plates would close as expected, but then they would continue to "march." That is, they would move ever so slightly for about 15 seconds in a marching rhythm.

At this point I hooked up our scan tool. One channel was connected to the TP-B signal pin 63, and the other channel monitored TAPW on pin 45, this being the command from the PCM. During power-up, voltage on pin 45 rose to above 2 volts as expected. As this happened, the TP-B voltage also rose to a peak of 3.85 volts. Then the "marching" movement starts.

This was seen on the scan tool as voltage spikes of less than 1 volt. During this period of spikes, no voltage change was seen at the TP-B sensor output. Also, during this period of activity, no traction telltale light would illuminate. It is only after this action ceases that the light comes on. Why is it doing this? Please help.

Frank Birkner, technician, Millville Tire, Millville, NJ

Dear Mr. Birkner, The Series Throttle Control system, which was used for traction control, was only used for a few years. I have heard of a couple of controllers being replaced for code P1220.

I also was told of a TP-B creating this code. I had one a few years back: A shop had replaced the controller, which seemed to have corrected the problem, but the code came back within a couple of weeks. This vehicle acted similarly to your description.

Because the problem was corrected for a short period of time by replacing the controller, I checked power and ground and then checked the connecter by sliding a drill bit into each female connector. One pin was very loose. Replacing that connector solved the problem.