2004 Jeep Grand Cherokee P0122: Throttle Position Sensor Circuit Low - Engine Stalls and Check Engine Light On
Hello, I own a 2004 Jeep Grand Cherokee with a 4.0L V6 engine. The check engine light has come on, and the vehicle is now acting like it's about to stall—puttering and losing power. I've diagnosed a P0122 code: 'Throttle Position Sensor (TPS) Circuit Low Voltage'. I have already replaced the throttle position sensor twice, the throttle cable, and the associated wiring harness. I’ve also changed the engine oil, installed new spark plugs, and replaced the oil filter—yet the issue persists. The problem seems to be electrical in nature. Based on my research, P0122 typically indicates a low voltage signal from the TPS sensor, which can stem from poor wiring connections or faulty connectors rather than a failing sensor itself. I’ve tried using a digital multimeter (DVOM) with a KOEO probe to test voltages at the TPS connector, but I haven’t completed a full diagnostic yet. I’m seeking advice on how to properly diagnose this issue—especially checking the voltage on the two outer wires of the TPS sensor while the engine is off and then during idle. Any guidance or troubleshooting steps would be greatly appreciated. Thank you, Angie
Angie, you're on the right track—but it's important to start this in the correct section: the Jeep-specific forum. This is a common issue with 2004 Grand Cherokee models equipped with 4.0L V6 engines. P0122 — Throttle Position Sensor (TPS) Voltage Low — indicates an electrical circuit problem, not necessarily a faulty sensor. The most likely causes are loose or corroded wiring at the TPS connector or poor contact in the electrical plug itself. To troubleshoot effectively: use a digital voltmeter (DVOM) with a KOEO probe to measure voltage on both outer terminals of the TPS while the engine is off and then during idle. A healthy signal should show stable readings between 0.5V and 4.5V depending on throttle position. I've seen many cases where the issue resolves simply by cleaning or replacing the electrical connector—ensure all pins are making solid contact, especially in damp or high-vibration environments.