This is going to be a bit long winded but here goes:
Just put 225/75R16 High Tec retreading muds on the '03 Grand Vitara 4x4. Rides and drives great, just rubs a bit on turns and stuff. A lift is coming to fix that.
To correct for the bigger tires I put on a Yellow Box speedo recalibrator from Black Robotics in Australia. It was recommended to me by a guy who put one on his '99 GV for similar reasons.
Installation wise you tap it's power wire to the '03's power wire going to the speedo (the '03 GV has 3 total wires - power, ground, and the ECM wire), ground to the factory sensor ground wire, and then snip the factory ECM wire in two. You connect the Yellow Box so that the ECM wire from the VSS in the transfer case goes to the Yellow Box first and then up to the ECM. This way, by flipping some switches, you can change the signal the ECM gets and correct your speed sensitive components all at once.
I installed the Yellow Box last weekend and left it in the neutral (doesn't affect the signal) position as the new tires had not arrived yet. Today we had the tires installed and after driving across town with the inaccurate speedo I dropped the wife off at work and started tinkering. I flipped the appropriate switches and according to my GPS am now indicating only slightly faster than the vehicle is actually going.
Shhhh....don't tell the wife but I left her lead foot a 2mph at 55mph buffer to keep her out of trouble.
So anyways, I drove it around some and tested it out, works great, rides great.  Accurate speedo and the trans is shifting fine.
Then I found a future subdivision that's roads were all covered in 6" of melting slush and snow. Eager to test the taller mud tires out I shifted into 4hi and went at it. Other than simply not touching the ground a few times it did excellent. FAR better than the carish tires it had from the factory. Never worried once. Then as I was leaving I noticed something.
The service engine light is on. Hmmm.......... a scan at the local parts store says it's code P1875:
4WD low switch circuit malfunction
The FSM explains it as this:
"While driving at higher than specified vehicle speed and with more than specified throttle valve opening, the following conditions are satisfied for specified time.
-Vehicle speed sensed by vehicle speed sensor is more than 10 km/h higher than that sensed by A/T output shaft speed sensor.
(2 driving cycle detection logic)"
It also says the following under the codes section:
"Difference between vehicle speed detected by VSS and vehicle speed detected by output speed sensor and compensated vy 4WD low switch is larger than specification."
What exactly is it saying and has anyone had this issue? I don't think there's any way the computer can tell what speed the VSS is actually reading as I've changed that signal in between the VSS and the ECM. So I should be good there...right? Are there any other sensors in the drivetrain where the OBD-II computer can tell how fast the wheels are turning? I'm kinda leaning towards that explanation but can't figure out where that sensor would be.
Or am I looking in the wrong direction and this is a 4WD problem? Oy, I'm confused. ??? It rides and drives just great and other than the SES light you'd never know anything was going on.
