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2003 Jeep Liberty 3.7L V6 P0306 Misfire: How to Diagnose and Fix the Issue

Model: 03 Jeep Liberty 3.7L V-6 Fault Code: P0306 Posted: 2010-04-14 05:28

I took my 2003 Jeep Liberty with a 3.7L V6 engine to a new mechanic, but I'm concerned about being misled. After sitting for several months, I started noticing an irregular popping sound coming from the engine—when it happens, it pushes the accelerator pedal against my foot. I've already replaced the spark plugs and checked the ignition wires, both of which have been confirmed as good. The mechanic scanned the system and reported two issues: 'Cylinder #6 misfire' (P0306) and a TP Sensor voltage above 4.5V. However, when I reviewed the OBD2 code list, I couldn't find the second one. The closest match is P1295 — indicating no 5V signal to the Throttle Position Sensor (TPS). I'm seeking advice on how to properly diagnose this issue and whether the TPS fault is directly related to the cylinder misfire. Any insights or troubleshooting steps would be greatly appreciated, especially for a vehicle with known common issues like those found in 3.7L V6 engines.

Related fault codes
P0306
Comments (3)
Anonymous 2010-04-14 09:21

Here's a practical step to diagnose the misfire: swap the coil pack from cylinder #6 with one from another cylinder and re-scan the vehicle. If the P0306 code moves to the new cylinder, it indicates a faulty coil pack. If the code stays on cylinder #6, then the issue is likely a bad valve—this is very common in 3.7L Jeep Liberty engines. Always check the coil pack and report back with your results. Also, perform a second scan after fixing the misfire to verify whether the TPS fault persists.

Anonymous 2010-04-16 05:50

Thanks for the advice! I'm trying to find a reliable mechanic and want to avoid being misled. What is the expected voltage at the Throttle Position Sensor (TPS), and does a TPS-related code directly affect cylinder #6 misfire? The 3.7L V6 engine has known reliability issues, so I’m looking for clear, accurate guidance. If it were an aircraft, I’d be confident—LOL!

Anonymous 2010-04-17 07:29

The Throttle Position Sensor (TPS) typically receives a reference voltage of 5.0V from the Powertrain Control Module (PCM). The output signal varies between approximately 0.26V when the throttle is fully closed and up to 4.49V when wide open. This data is used by the PCM to adjust ignition timing and fuel injection across all cylinders—so a TPS fault would affect engine performance generally, not just one cylinder. Therefore, while the TPS issue may contribute to overall drivability problems, it's unlikely to be directly causing the P0306 misfire on cylinder #6. As such, I recommend addressing the misfire first by replacing or testing the coil pack. Once the misfire is resolved and the code cleared, perform a second scan to check if the TPS fault reappears. I also agree with the suggestion to swap coils—this is one of the most effective ways to isolate ignition-related faults in this engine model.