C0900

C0900 means the Cruise Control Throttle Actuator has a circuit or performance fault — on older mechanical cruise systems this referred to the vacuum-actuator servo or stepper motor that physically pulled the throttle cable, but on any 2003-and-newer drive-by-wire vehicle (which is essentially every passenger car since the late 2000s) C0900 traces back to the electronic throttle body itself or to the cruise function's command path through the PCM. Diagnostic order, cheapest first: (1) Scan live data on the throttle position sensor — modern ETBs have two redundant TPS sensors built in that should track each other across the 0-100% range; if TPS1 and TPS2 disagree by more than 3-5%, the ETB is faulty internally. (2) Check the throttle pedal position sensor (APP) for the same redundant pair behavior. (3) Inspect the throttle body for carbon buildup at the throttle plate — a carbon-stuck plate makes the ETB miss closed-position relearn and the cruise function fails its rationality check; a 15-minute throttle body cleaning with CRC throttle body spray and a soft brush ($8 of consumables) resolves a surprising number of C0900s on high-mileage GM and Toyota vehicles. (4) Verify the brake-pedal position switch is reporting correctly — a stuck-closed brake switch tells the cruise function 'brake is pressed' permanently and the throttle actuator command is blocked. (5) On the small minority of vehicles still using a separate cruise servo (some 1990s-early-2000s vehicles with cable throttle), test servo coil resistance per FSM and check vacuum supply to the servo can. Always perform the throttle-body idle-relearn procedure after any TB service — a TB that's mechanically clean but hasn't relearned closed position will still throw C0900 alongside P2111 / P2112.

Vehicle-specific patterns: any drive-by-wire GM Vortec V8 from 2007+ (LMG 5.3L, L96 6.0L, L86 6.2L in Silverado, Sierra, Tahoe, Yukon, Suburban, Escalade) and any Ford EcoBoost from 2011+ (1.5L, 2.0L, 2.3L EB, 2.7L, 3.5L EB) handle cruise through the PCM/ETB rather than a discrete servo, so C0900 on these is virtually always a throttle-body cleaning or a TPS-sensor ETB replacement. 2005-2010 Chevy Cobalt / HHR / Malibu throws C0900 alongside the larger ignition-recall family when the ignition switch intermittently kills 12V to the ETB. 2003-2009 Toyota 4Runner / Tacoma / Tundra throws C0900 from a failed APP (accelerator pedal position) sensor — Toyota issued multiple TSBs and the APP module is a sealed pedal assembly that swaps in 20 minutes. 2007-2014 Dodge / Chrysler / Jeep with TIPM gateway issues throws C0900 alongside U0405 when the TIPM CAN transceiver fails. 2008-2013 Honda Accord / Pilot / Odyssey with the J35 V6 throws C0900 from carbon-clogged throttle bodies that need cleaning + idle-relearn at every 60k-mile service interval. Estimated repair: $8 (throttle-body cleaning consumables) to $650 (full electronic throttle-body assembly with PCM relearn).