P0123 TPS Fault Diagnosis and Repair for 2000 Dodge Durango (125K Miles)
Hello everyone, I own a 2000 Dodge Durango with 125,000 miles. It has been in excellent condition overall and runs smoothly when towing my 31-foot boat. However, I've recently noticed severe engine misfires and significant stalling issues. The vehicle is now displaying the following OBD-II diagnostic codes: - P0123: Throttle Position Sensor (TPS) Circuit Low Signal - P0133: Oxygen Sensor Heater Circuit Malfunction - P0171: System Too Lean (Fuel Mixture) I've tested the TPS and confirmed it has proper ground connection and outputs 5V at idle. The signal wire to the Powertrain Control Module (PCM) also reads 5V, which is consistent with expected values. However, the voltage does not vary appropriately as the throttle opens or closes — a key indicator of proper TPS function. I've verified the wiring harness and connections, and all appear intact. The TPS signal waveform shows no abnormal behavior during operation. Given that P0133 and P0171 are likely linked to an incorrect air-fuel mixture, I'm wondering if this could be a faulty PCM or a deeper issue with sensor calibration. Has anyone encountered this exact scenario before? Any insights or troubleshooting steps would be greatly appreciated. Thanks in advance!
Throttle Position Sensors (TPS) are one of the most common failure points on Dodge Magnum series engines (3.9L, 5.2L, -5.9L), often outperforming ignition system components like spark plugs, cap, rotor, and coils. It's essential to use an oscilloscope to monitor the TPS signal waveform for proper ramp-up and ramp-down behavior. At my dealership, we've replaced TPS units approximately three times per week — they're relatively inexpensive and easy to install as long as the throttle body mounting screw doesn't break.