How is the MPH being calculated?

[ninaandphil]

Probably a daft question, but my ZT CDTi currently has an ABS fault on the drivers front side, resulting in no speedo dial. From my understanding, the speedo works by reading a signal from the ABS sensor.....

So being a gadget lover, my HUD gizmo arrived from China today, which I duly plugged into the OBD2 port to try. I had expected not to see any MPH figure of course.... but to my surprise, the HUD is providing an accurate speed projection on to the windscreen when driving.

My question is, how is does the OBD2 port provide an accurate speed of the car when the ABS sensor and the car speedo are faulty?

PS, the car is going in on Monday for the DSF bearing to be replaced as a new sensor cable has failed to fix the fault despite many attempts to clean out the holder and fiddle! Hope that cures the issue

[raykay]

Originally Posted by ninaandphil

My question is, how is does the OBD2 port provide an accurate speed of the car when the ABS sensor and the car speedo are faulty?

The input for the speedo is from the front offside sensor, for the ABS, Cruise Control and Navigation system it is the front nearside sensor.

The ABS ECU is also connected to pin 8 of the OBD2 port, which may be where you are getting the MPH signal from.