GMC/CHEVROLET: SIR MIL ON AND TECH 2 WILL NOT COMMUNICATE WITH SDM. SOME MODULES MAY SET A COMMUNICATION DTC U0151 AGAINST SDM. DIAGNOSTICS MAY LEAD TO REPLACEMENT OF SDM AND REPLACING SDM MAY FIX THE CONCERN FOR A SHORT TIME OR IT MAY FAIL AGAIN ON THE FIRST OR SECOND IGNITION KEY CYCLE. THE HD SILVERADO AND SIERRAS ONLY. *PE