[pontiacmonstr]

i have a 1998 grand cherokee. check engine light is on. i ran the code with a scanner. comes back as a speed sensor. advance auto has 2 different ones. they look nothing alike. my speedo and odometer work fine. i cleared the code, put it in drive, as soon as i start to move, the light comes back on. if i clear the code and just let it idle, it won't come on. i have 235/75/15 tires currently. i believe the originals were smaller. could the tire size be the proble tripping the light? what can i do besides going back to the original size? thanks!

[kngstrk]

Had this problem on past Jeeps, try the crankshaft speed sensor, typically located on the left side of the bell housing.

[salem1912]

What was the P-code? Tire size won't cause the lite.

[kustomlarry]

I have been having the check engine light demon problem with my 2000 cherokee. Sucks. Love the car. 198k and still rollin....AMC motors rule. My code is for the gas cap. Bastards.

[mechanickeith]

Tire size CAN kick a code. Computer knows what road speed is for a certain gear & RPM. Different size tire will have a wrong speed for the RPM, code pops up. Also, changing one tire on a newer car will kick a code. Different manufacture have different rolling speeds for their tires, even if they are the same size. 2 different brands of tires will kock a code. That said, is the code popping up instantly?? Or does it take a day or 2 to come back?? Could still be a speed sensor.

[BB70]

Without more scan tool info & a code number, I would suspect the output speed sensor on the trans. I believe it has 3 sensors, input, output and vss sensor. Input & output are used to determine internal trans slippage. Usually it won't shift properly when the output sensor drops out. Hope this helps. John