VSS and Brakes

[Robby1870]

Okay, before the guideplates broke, I noticed some things. When I just touched the brakes enough for the lights to come, the speedo would jump around, even I was not slowing down or speeding up, then when I let off it would be fine. Also, the speedo was sorta choppy and bouncy at highway speeds around 70mph. So, Im thinkin maybe the VSS is going out. Also, does anyone know how or if the VSS signal and the "brakes on" signal are inter-connected? TIA

 

Robby

[brian89gp]

The only thing I can think of is something in the guage cluster that happens with the voltage dip when the brake lights come on. The VSS is hooked directly to the ECM (the brake switch isn't), the ECM then outputs a 4k per mile pulse on a single wire which is used for cruise and the dash. The brakes are hooked into the brake lights and the TCC, if the speedo jumps around when you tap the brakes when the TCC isn't engauged then it isn't that.

[Robby1870]

yeah, it does it in any gear, and since the TC isnt lockup until after Im in 3rd, then thats not it. Im thinking Im just having a power loss somewhere, but the battery and alternator both checked out fine at Advance. I dont know, its confusing me. Im maybe thinking that the voltage regulator in alternator has gotten fried, and a test at advance wont show that, I dont think. I was watching the voltage with the car at idle, and had my brother put the A/C on, hit the brakes and stuff like that, and turning the A/C on, made the voltage at the battery go up. That is very counterintuitive, it should go down. But, it went up from like 12.5 to 13.5, so it was undercharging anyway. I really have no clue. Also, I would think that one gauge went bad due to a lack in voltage, the others would go stupid too, but they havent. Im lost on this problem

 

Robby