PO121 : TP Sensor Performance
The PCM supplies 5V to the TPS - Throttle Position Sensor
. The TP sensor is a variable resistor that drops the voltage to about 4 volts at WOT(wide open throttle) to less than 1 volt at closed throttle. Some TP sensors are adjustable. others have a learn procedure to determine closed throttle.
PO171 Fuel Trim System Lean
In closed loop the PCM adjusts fuel delivery based on H2OS
1 readings and is indicated by long short fuel trim values. If lean the PCM will add fuel (fuel trim above 0%) if rich the PCM will reduce fuel(fuel trim below 0%)
PO128 ECT Below Thermostat Regulating Temperature
possible failed thermostat
, low or empty on coolant,
Engine Coolant Temp Sensor, Poor connection/Harness/Wires, faulty PCM Connection.