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Vehicle Speed erratic VR4


Dan P

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The vehicle speed reading is bouncing around, lets say I'm trying to cruise at 40 and it will spike around to 90, 60, 50,30 and sometimes a ridiculous number like 2000.  It can have periods where its nice and steady but just a few seconds then its back to being crazy.  At lower speeds it doesn't seem affected as much.  I've tried replacing the gauge cluster because the VSS is built into it (cable driven speedo with reed switch output to ECU 4 pulses per revolution).  I also tried bypassing the factory harness and ran my own signal wire from the reed switch to the ECU, and rewired its ground source to sensor ground at ECU.  Pullup is on, no reading without it.  Falling or Rising edge makes no difference. Wired to DI3, LF Wheel Speed, Calibration = 250.  I highly doubt I need shielded wire as I never see this on a VSS...please help!

 

VSS logging.llg

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Best way to fault find this would be to have a scope on the signal to see what is happening. 

You could also se the input on the ECU to a Frequency input and see if that gives an unstable frequency

 

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