A TPS - throttle position sensor is simply a variable resistor that changes in resistance as the throttle opens and closes. This resistance is translated into voltages in reference to the 5v reference voltage. This voltages indicates to the ECM what to do concerning ignition timing and fuel control. The TP sensor is used by the PCM for clear flood mode, torque converter engagement and release, and automotive transmission shift points, as well as for rationality testing for the MAP and MAF sensors. If the PCM detects that the throttle is at or close to wide open, the air-conditioning compressor is disengaged.
P0122 & P0123 Symptoms
Check engine light
Erratic transmission shifting points
Compressor keeps running at wide open throttle.
P0122 & P0123 Causes are
Faulty PCM voltage or grounds
Signal wires open or shorting to ground or power
Dirty throttle or defective linkages
Faulty TPS sensor, or incorrect VSS or MAP
P0122 & P0123 - DYI Steps to fix it
STEP 1: CHECK ENTIRE TPS SENSOR CIRCUIT
Most TPS have three wires: power (usually 5 volts), grounds and signal. A TPS can be tested in two ways: by measuring either varying voltage or resistance. Voltage measurement is always the ideal test method because it give accurate results and most ECM, PCM reads these voltages. To check for the presence of TPS signal, turn the ignition key to ON position and leave the TPS plugged in. Back probe each wire with a digital multimeter. The following readings should be found on each of the three TPS wires:
STEP 1: A 5volts on one of the 3 wires indicates voltage coming from the ECM/PCM as a reference voltage. If you don’t get 5volts on any of the wires, first check the fuse that powers the ECM/PCM. If good check the wire carrying the current from the ECM/PCM for opens or shorts to ground. If the wire is good, then the voltage regulator inside the ECM/PCM is bad, replace the PCM.
STEP 2: A ground (0v or 0.02v) on one of the 3 wires indicates grounding coming from the ECM/PCM. If its higher that 0.02volts there is possibility that circuit has high resistance or bad ground. Perform a voltage drop test on the ECM/PCM ground wire. To run a voltage drop test Click on this sentence.
STEP 3: The signal wire must not be either 5volts or 0v. At the same time it must vary from 0.5volts if the throttle is closed to 4.5volts if the throttle is open wide. This is due to the variable resistor inside the sensor that changes resistance in relationship to the throttle angle (opening). If you realised the voltage keeps skipping and jumping around, change the TPS sensor. If possible use a scope meter to confirm. But if it’s stuck to 5v or 0v it means the sensor is shorting to power or shorting to ground. In cases like this run a signal circuit integrity test first to confirm before replacing the sensor.
STEP 4: A code scanner will display P0122 (low voltage - sensor or wire shorting to ground or open) or P0123 (high voltage-sensor or wiring shorting to voltage, or open ground) or P0121 ( conflict with MAP & incorrect Vehicle Speed sensor). To be double sure plot the PID graph for the TPS throttle position sensor (Volts) and the IAC idle air control (%). As you depressed the accelerator to open the throttle watch out for increment in numbers for both TPS & IAC. This shows they are both working perfectly. Anything different indicates faulty TPS.
STEP 5: Service throttle linkage if its stuck or binding after inspection, which affects idle speed measurement..
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