Under reading speedo

[legacyau]

Hi , i have a 93 vtd equipped svx, with a jdm auto fitted, speedo uses the rear sensor only and until recently was accurate, it now reads up to 20 kph under actual road speed, the cruise control still works and holds the set speed per gps readings, could the speedo be lazy? its got me puzzled

cam

[1986nate]

Seems like it would point to the gauge cluster failing.

[b3lha]

Originally Posted by legacyau

Hi , i have a 93 vtd equipped svx, with a jdm auto fitted,

So presumably you swapped the Aussie speed sensors into the JDM transmission so it would work with an Aussie TCU? Or are you using the JDM sensors and a JDM TCU as well?

Originally Posted by legacyau

speedo uses the rear sensor only

Speedo is normally driven by the front sensor. Have you done some kind of custom wiring? On the JDM system the speedo is driven directly by the front sensor. On the Aussie system, the TCU processes the front sensor signal and outputs a separate signal to drive the speedo.

Originally Posted by legacyau

and until recently was accurate, it now reads up to 20 kph under actual road speed, the cruise control still works and holds the set speed per gps readings, could the speedo be lazy? its got me puzzled
cam

Are your wheels and tyres the correct size and properly inflated?

It does sound like it could be the gauge cluster. Have you ever pulled the needle off to change speedo face? It's very hard to get it back on right.

Is the max cruise control speed the same as it was before, or has that dropped as well. On my JDM, the max cruise control speed is about 110km/h, I presume Aussie is about the same.

Do you have any error codes in the TCU or unusual transmission behaviour that would indicate the TCU receiving incorrect readings from the sensors? Could you get hold of a select monitor to read what speed the TCU is getting from the sensors?

Phil.

[legacyau]

the swap to the JDM trans was plug and play, jdm box audm tcu, disconnected duty C solenoid, the speedo just worked till recently the cruise control is working as it should, so im thinking the cluster is the culprit, tyres are 235/45-17 Sti wheels, max speed for cruise is whatever the car will do