Express 1/2 Ton Van V8-305 5.0L VIN M SFI (1998)
Speedometer Head: Technical Service Bulletins
Instruments - Speedometer Accuracy Information
INFORMATION
Bulletin No.: 08-08-49-011B
Date: September 05, 2008
Subject:
Information On Speedometer Accuracy
Models:
1997-1999 GM Passenger Cars And Trucks
2004-2009 Cadillac XLR
2005-2009 Chevrolet Corvette
2007-2009 GMC Acadia
Supercede:
This bulletin is being revised to add the GMC Acadia. Please discard Corporate Bulletin Number 08-08-49-011A (Section 08 - Body and Accessories).
The speedometer used on most GM vehicles are of the Air-Core design. This is a moving needle operated by a magnetic coil. Because there is no direct
mechanical linkage, there is some variation in accuracy that cannot be eliminated.
Digital readout devices, such as some speedometer displays and Head-Up Displays (HUD), are direct readouts of the Vehicle Speed Sensor (VSS) and
their accuracy is much greater. Tire size, tread life and inflation may cause some variation in the readings. In addition, the Tech 2(R) reads the VSS
directly and is quite accurate.
Questions on speedometer accuracy can usually be resolved by comparing the speedometer reading to the Tech 2 while driving. The table shown above
lists allowable speedometer variations. Any Air-Core speedometer that reads within these limits should not be returned for service.
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