Have a 1998 Chevy K3500 utility truck. Sometimes when you start it the tach and speedo will not come on. When this happens the trans will not shift out of second. When you turn on the heater fan the ABS light comes on for a while. If you shift to 4 wheel drive the fan will shut off. Auto part store put it on a dignostic and it said the left front wheel sensor missing and Abs not working. Is it just the wheel sensor grounding out or is it the engine control module?