P1516

P1516 sets when the Throttle Actuator Control Module (the PCM's internal ETC monitor) detects that the throttle blade position does not agree with the commanded position within tolerance — typically the actual TPS reading differs from commanded by more than 8-10% for longer than 200 ms, or the rate-of-change doesn't match the commanded slew rate. This is a safety-critical code: most platforms force Reduced Power Mode and limit RPM to 1500-2000 once P1516 sets. Diagnose with the engine off, key on: scan-tool both TPS sensors (modern GM ETC bodies have two redundant 5V Hall sensors reading 0.5V/4.5V and 4.5V/0.5V counter-rotating) and verify they sweep smoothly and oppositely as you blip the throttle body manually with a clean finger. If both sensors track correctly but the blade won't move to commanded position under PCM control, the throttle body motor is failing or the gear train has carbon buildup binding the blade — remove the intake duct and inspect the bore for the brown carbon ring that prevents full closure. The expensive misdiagnosis: throwing a $350 throttle body at the car when a 20-minute throttle-body cleaning with the blade held open would have restored normal sweep.

Vehicle-specific patterns: 2005-2010 Cobalt/HHR/Malibu 2.2L/2.4L Ecotec is the leading P1516 platform — the throttle body motor brushes wear and the blade sticks during cold-start commanded sweeps. 2007-2010 Tahoe/Yukon/Silverado 5.3L sees P1516 from carbon buildup on the blade documented in PIP4569 — clean before replace. 2004-2008 Grand Prix 3.8L Series III throws P1516 when the throttle-body 5V reference shares with a failing MAP sensor and pulls the reference low. 2008-2012 Acadia/Traverse/Enclave 3.6L LY7 gets P1516 from internal throttle body motor failure (a known wear item by 100K). Estimated repair: $90 to $480.