Hi guys, I'm looking for advice on what seems to be an unusual problem. My truck's speedometer normally behaves perfectly, except when I'm driving at 72-78mph! Then, it jumps all over the place; my edge tuner reports 30-206mph! once I get up to 80mph, the speedo smooths out again and reports accurately. Slowing down from 80mph, the speedo goes crazy again through that same range. Typically the parking brake and ABS lights come on when this is happening. Sometimes the check engine light comes on too, throwing a "speed sensor" or "transmission communications bus" code and puts the transmission into limp mode (5th gear no lockup) until I shut off and restart the engine. If the transmission is limping, the speedo still behaves the same way.
I've replaced the speed sensor in the transfer case but it had little or no effect. The old speed sensor had minor wear on it, like it had rubbed. At this point the dealer says that the reluctor wheel in the transfer case may be at fault. Also FYI, the gauge cluster was replaced 3 times under warranty by the first owner of the truck according to GM's records.
Any ideas?
I've replaced the speed sensor in the transfer case but it had little or no effect. The old speed sensor had minor wear on it, like it had rubbed. At this point the dealer says that the reluctor wheel in the transfer case may be at fault. Also FYI, the gauge cluster was replaced 3 times under warranty by the first owner of the truck according to GM's records.
Any ideas?