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Q: My truck is stuck in 4L or 4H also the speedometer is saying I'm going 100 mph when I'm only going 20 mph. Is my GEM Module bad?

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Im not sure if the 4 wheel drive switch has gone out or the gem module is bad or if something else is wrong because my truck is acting like its stuck in 4H or 4L. And the speedometer is screwed up saying im going 100mph when im only going 20mph-25mph. Also the 4x4 is flashing on my dash when the switch is on the normal setting AW4WD but when I turn it to 4H or 4L it stops flashing and doesn't even light up on dash.

My car has 200000 miles.
My car has an automatic transmission.

Hi there. The issue could be with the output shaft speed sensor on the tail shaft of the transfer case. The output shaft speed sensor is a sensor the registers the speed of the output shaft and lets the computer (ECM) know how fast the vehicle is going. If the output shaft speed sensor is working properly, then there is an issue with the electrical wiring from the output shaft speed sensor and the dashboard. If you need further assistance with the speedometer and 4WD acting up, then seek out a professional, such as one from Your Mechanic, to help you.

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