P1129

P1129 on a Toyota is the general Electric Throttle Control System Malfunction set — it's the catch-all ETCS-i code that sets when the ECM has detected a fault inside the throttle control logic that doesn't fit cleanly into P1125 (motor circuit), P1127 (power source), or P1128 (motor lock). Common triggers: TPS1 and TPS2 disagreement greater than 10% of full-scale (the throttle body carries dual redundant TPS sensors and the ECM cross-checks them constantly), an internal H-bridge driver fault inside the ECM, or a software watchdog timeout in the throttle control loop. Cheapest-first ladder: (1) scan live data for TPS1 and TPS2 voltages with key on and the pedal slowly swept from rest to wide-open — both signals should track in opposite directions (one rising 0.5V to 4.5V, the other falling 4.5V to 0.5V on most Toyota ETCS-i variants) with <3% disagreement at any single sample point. If they diverge more than 10% at any blade angle, the TPS pair is the fault. (2) Inspect the throttle body harness for chafing or a partial short — a single broken TPS signal wire often presents as P1129 because both sensors share the harness path to the ECM. (3) Confirm 5V reference at the TPS connector (should be 4.9-5.1V); a sagging 5V reference can pull both TPS readings toward each other and trigger the cross-check fault without either sensor being independently bad. Expensive-misdiagnosis caveat: don't replace the ECM for P1129 — Toyota ECMs almost never fail internally in a way that throws P1129; the fault is in the throttle body (TPS pair) or the harness about 95% of the time, and a $1,200 ECM is the wrong answer when a $400 throttle body or $40 harness repair would have closed it.

Vehicle-specific patterns: 2002-2011 Camry 2.4L (2AZ-FE) and 3.0/3.5L (1MZ-FE, 2GR-FE) throw P1129 most often from TPS pair drift around 120K-150K mi — the dual potentiometers wear unevenly as the blade cycles. 2004-2013 Highlander 3.3/3.5L (3MZ-FE, 2GR-FE) and 2004-2010 Sienna 3.3/3.5L share the same TPS architecture and the same drift pattern. 2007-2012 RAV4 2.5L (2AR-FE) throws P1129 with a slightly later mileage onset (~140K-180K mi) and the TPS replacement is the durable fix. 2006-2013 Lexus IS250/IS350 (4GR-FSE, 2GR-FSE) and GS350 (2GR-FSE) throw P1129 with similar timing — Lexus throttle bodies are the same part-family as Toyota's and fail the same way. Estimated repair: $80 to $550.