Speedometer Correction for Non-Stock Tire Sizes
#11
01-09-2011, 12:14 PM
For 98+ years.
Chassis Diagnostic Manual. There, in section 29A, it explains the procedure needed to program the CAB for specific tire sizes. [The CAB sends a pulse stream to the PCM, which drives the speedo/odo; to change the calibration, the CAB needs to be told, among other things, the number of teeth on the RWAL sense ring and the rev/mi of the installed tires.]
So, if you change your tire size and your dealer hasn't a clue as to correcting the speed/odo, point him to the Chassis Diagnostic Manual, section 29A. It's all there.
NOTE: the 98 1/2 models do not use speedometer gears and the speed metering is taken from the ABS sensors. To change "gears" for different tire sizes requires reprogramming of the PCM. Dealers have been having problems with this procedure, and many axle ratio/tire size combination's are not available.
For 98 and under years
http://www.go.jeep-xj.info/HowtoSpeedoGears.htm
Chassis Diagnostic Manual. There, in section 29A, it explains the procedure needed to program the CAB for specific tire sizes. [The CAB sends a pulse stream to the PCM, which drives the speedo/odo; to change the calibration, the CAB needs to be told, among other things, the number of teeth on the RWAL sense ring and the rev/mi of the installed tires.]
So, if you change your tire size and your dealer hasn't a clue as to correcting the speed/odo, point him to the Chassis Diagnostic Manual, section 29A. It's all there.
NOTE: the 98 1/2 models do not use speedometer gears and the speed metering is taken from the ABS sensors. To change "gears" for different tire sizes requires reprogramming of the PCM. Dealers have been having problems with this procedure, and many axle ratio/tire size combination's are not available.
For 98 and under years
http://www.go.jeep-xj.info/HowtoSpeedoGears.htm
he just needs to look for a VSS in the tail housing of his t-case. they make speedo gears for up to 37" tires
#12
01-09-2011, 05:29 PM
