Rick's Free Auto Repair Advice

Dead gauges GM trucks

Fix Dead gauges GM trucks

GM has issued a Technical Service Bulletin (1549143) for Dead gauges GM trucks 2001-05 Chevrolet Silverado and GMC Sierras equipped with the Allison LCT1000 transmission. The instrument cluster can be erratic, drop out, become inoperative, or result in a trouble code of P0721, C0237, P0500, C0055. In addition, the transmission may exhibit trouble shifting. Also, the ABS light can illuminate. The problem may be caused by a bad vehicle speed sensor (VSS) or a damaged reluctor wheel.
The Allison tranmission sends a speed signal to the transmission control module. The signal is AC voltage of 34Hz at 1MPH. The transmission control module converts the AC signal to a digital waveform and sends it to the powertrain control module. That speed signal is then fed to the instrument cluster, radio, ABS brake module and the cruise control. So a bad VSS can be the source of all these problems. I could tell you how to test the sensor, but you’d need an expensive Fluke multimeter. It’s cheaper to replace the sensor.

© 2012 Rick Muscoplat

Posted on by Rick Muscoplat


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