P0122

P0122 means the Throttle Position Sensor signal voltage is below the floor, typically under 0.2V on a 3-wire potentiometer or under the TPS1 minimum (around 0.3V) on a 6-wire ETC. The ECM reads that as a closed-throttle signal that physically cannot be lower than the calibrated rest position, which means either the sensor has failed shorted to ground, the signal wire is grounded in the harness, or the 5V reference has dropped out and pulled the signal with it. On most platforms the engine drops to a hard limp-home idle (1000-1200 RPM, no pedal response or severely reduced authority) when P0122 sets, because the ECM cannot trust the throttle reading. Cheapest-first ladder: key-on engine-off, unplug the TPS connector and backprobe the signal pin at the harness side; with the connector unplugged the signal pin should float to 5V (open-circuit reference). If it stays at 0V with the sensor unplugged, the signal wire is shorted to ground between the connector and the ECM. If it goes to 5V unplugged but drops to 0V plugged in, the sensor is internally shorted. Verify the 5V reference at the connector reads 4.9-5.1V and ground integrity is under 0.1V drop. Don't replace the throttle body before checking the connector for moisture intrusion, because a wet connector will short signal to ground and mimic a dead sensor exactly.

Vehicle-specific patterns: 2002-2007 Jeep Liberty 3.7L sees P0122 frequently from a chafed TPS signal wire where the harness routes past the intake manifold bracket, shorting the signal to ground intermittently before going hard-fault. 2003-2008 Honda Pilot/Odyssey J35 V6 with cable-actuated throttle sees P0122 from internal TPS wiper failure where the element shorts to the case ground at the closed-throttle position. 2007-2014 GM 5.3L/6.0L Silverado, Tahoe sees P0122 from the throttle body internal TPS1 element failing shorted; the entire throttle body is the GM replacement and it requires a relearn. 2005-2010 Dodge Charger/Magnum 5.7L Hemi sees P0122 from a known-defective lot of ETC throttle bodies, Mopar TSB acknowledged failures. Estimated repair: $80 to $450.