P2100

P2100 means the ECM has lost continuity on the throttle actuator control motor circuit — the electric motor that physically opens and closes the throttle blade on a drive-by-wire (ETC) system isn't responding, or its circuit reads as open. This is not a sensor code; this is the actuator itself or its dedicated H-bridge driver in the ECM. The car will be in limp-home mode within seconds of this code setting — typically forced idle around 1,000-1,500 RPM with a hard cap that won't let you above 25-30 mph. Cheapest-first diagnostic: pop the throttle body off and look at the blade. If it's coated in coffee-ground carbon (the norm past 60k miles), a $100 throttle-body cleaning service often clears it because the motor was binding against deposits and the ECM finally gave up. If the blade is clean, inspect the 6-pin connector at the throttle body for backed-out pins, green corrosion, or melted plastic from exhaust-manifold heat soak. Then backprobe the two motor-drive wires with a DMM keyed-on — you should see roughly battery voltage on one and ground on the other as the ECM commands the blade open, then they should reverse to spring it closed. If both pins read 0V or both read battery, the ECM driver is dead; if one reads battery and the motor doesn't move, the motor winding is open.

Vehicle-specific patterns: 2005-2010 Ford Five Hundred / Taurus / Mercury Montego with the 3.0L Duratec is the classic P2100 callback — the throttle-body actuator motor brushes wear out around 90-120k miles and the entire throttle body has to be replaced (Ford doesn't sell the motor separately), running $300-500 in parts plus an hour of labor and the relearn. 2003-2007 Cadillac CTS / SRX with the 3.6L LY7 throws P2100 from the same wear-out pattern, often with a P2101 companion code. 2007-2012 Nissan Altima / Maxima VQ35 sees P2100 from a known harness chafe at the throttle-body connector where it routes over the valve cover — repin or replace the pigtail and the code clears. 2008-2014 Mini Cooper R56 throws P2100 from internal water intrusion into the throttle body when the cowl drains plug; dry it out and reseal the cowl. Critical: NEVER clear a P2100 without running the throttle-relearn procedure (key-on / engine-off / 30-second wait / cycle key) — the ECM stores blade-stop positions in volatile memory and a fresh install with no relearn will throw the code right back in 5 miles.