Speedo Problem

[Griz]

Hi guys,
Been having a weird issue with my speedo of late & was wondering if anyone else had come across it before.

I was on the freeway and the speedo on the dash was reading 110, but the digital speedo was saying 100. I pulled over & turned the car off to reset & see if it fixed it, this time the digital speedo was 10 in front of the dash one. I tested it and it seems the faster I go , the bigger the difference. I don't know which one is right so I have been using whichever on is ahead at the time so I don't get done for speeding.

Any ideas?

 

[Benboy]

Vehicles in Australia are required to have a speedo that reads fast. I don't recall the exact tolerance permitted but I do know that a Commodore speedo can be up to 5 km/ph fast at 100 km/ph. Mine consistently shows 3 km/ph at 60 - 80 - 110 Why yours was up to 10 km/ph fast is a mystery. Have you or previous owner changed wheels or tyres to non-standard sizes (compared with what the vehicle left the factory with.) ?

 

[Griz]

Vehicles in Australia are required to have a speedo that reads fast. I don't recall the exact tolerance permitted but I do know that a Commodore speedo can be up to 5 km/ph fast at 100 km/ph. Mine consistently shows 3 km/ph at 60 - 80 - 110 Why yours was up to 10 km/ph fast is a mystery. Have you or previous owner changed wheels or tyres to non-standard sizes (compared with what the vehicle left the factory with.) ?

I brought the car with the current wheels & tyres on it which are not factory. They are 245/40/18. I have also noticed on occasion the speedo on the dash will not go back to zero when idle, it sometimes sits at between 10-20, but this does not always occur. Would I be safer to take notice of the in dash speedo over the digital one? Or should I just go of whichever is lower at the time.

 

[99notout]

If your wheel and tyre profile are not what it came with from the factory, then the pulses per kilometer will be out, and you will not get an accurate reading. The analogue (dial) speedo should read the same as the digital one though, even if it isn't accurate. The PPK rate can be reset with a Tech 2 very easily though.

 

[XUV]

Don't they have 2 reading points, ie dash speedo is off gearbox and digital speedo is off front wheels and more correct.

 

[99notout]

Don't they have 2 reading points, ie dash speedo is off gearbox and digital speedo is off front wheels and more correct.

No, just of the box. Put your car on a dyno and watch the speedo work just fine with the front wheels stationary.