What could cause this erroneous speed reading? The duration of the 400kph peak is about 0.5 seconds. Speed readings are otherwise good and I’ve never seen an issue like this with the driven axle reading.
I’m using the stock speedometer sensor (a reed switch mounted on the transmission that responds to 8 magnets mounted on a disk attached to the output ring gear). I’m tapping the pulsed 12V signal at the stock speedometer.
Here’s my configuration. There have been no changes since initial set up. I’ve been on V3.054 since it was released.
I’ve had this problem on V2 and V3 using a gps speedo module. From 0 MPH once moving I can get a spike to like 200MPH + for a split second then it goes to reading normally.
I’m guessing (and I do mean guessing) the issue is noise on the speedometer input. The sensor is a simple reed switch that is closed by magnets that rotate with the differential ring gear. Maybe the switch is “chattering” when a magnet moves by slowly? It’s purely mechanical, there’s noting to “debounce” the input. Maybe I need to increase the filtering?
This is happening during a slow roll in traffic. The VSS frequency before the spike is 0 and 1.13 Hz after. Axle speed before is 0.13 and increases to 6.94 kph after the spike. The spike is about 0.5 seconds in duration. Reviewing my entire log, I see this is happening often. Always at low speed.
