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- Posts: 2
- Joined: Tue Mar 08, 2022 2:58 pm
On a y 2k Chevy express the speedo shows 60 mile/h while doing 60km/h on the same time the needle goes up and down. So there is no clear speed signal. everything points in the speed sensors direction and the vehicle has all the signs. ABS light goes on from time to time the gear shift is not good no fault codes in ecu. After changing the speed sensor the fault remains the same. We don't find a wiring diagram online but after some searching we find that the 2 sensor wires are can high and can low so we hook up the picoscope on both wires to see the signal on those wires. The sensor is like the abs speed sensor, its magnetic 2 wire and there is a gear turning in front of the sensor just like the abs sensor. at stand still the voltage is 4 volts on the can high and 0 volt on can low. there is no noise showing on the scope. When driving the can high shows a sinus wave. the wave voltage goes up with the speed and at speeds over 30km/h the wave starts to modulate in amplitude like AM radio wave. We expected to see a PWM signal and not a sinus. So without the correct wave form we are stuck at this moment. has someone the correct wave form so we can follow this signal further to the ECU. We read somewhere that there is a Speedsignal buffer on this line is that correct. Also a wiring diagram would be very helpfull