Our shop recently took in a 1995 Ford F-250 with erratic downshift concerns. I started the initial evaluation with a visual inspection, fluids check, and a code scan. When scanning for codes, I was a little surprised that there weren’t any stored; per the customer concern, I was expecting an MLPS or a VSS code
A 1995 Lincoln Continental with an AX4N transmission comes into the shop with a gear-ratio-error code. As you are going through the diagnostic routine, you have pretty much determined that the unit needs to come out. But before you remove it, you decide to check for a glitch in the vehicle-speed sensor (VSS).
The speed buffer in a GM vehicle (see Figure 1) is a familiar piece of hardware for most transmission technicians. And its operation of taking an AC voltage signal from a speed sensor and converting it to a DC pulse signal for the computer is just as familiar. But what does come as a surprise to many is that Chrysler uses a similar speed-signal strategy for many of its passenger cars and vans.