Working on '06 GMC C7500, 8.1 V8 Gas, Allison: Unit has very occasional (1 time in hundreds 0r 10 in a row) engine de-rate and P1516 code setting. First code read showed P102 MAF, P0327 knock sensor, P1516 & P2101 "throttle actuator position perfromance". Subs... Login to read more.