← Back to list

2000 Lincoln Town Car 4.6L: P1131/P1151 O2 Sensor & PO303-PO308 Misfire Codes - Diagnosis Tips

Model: 2000 Lincoln Town Car Fault Code: P0300 Posted: 2016-09-10 15:00

I own a 2000 Lincoln Town Car with 140,000 miles and a 4.6L coil-on-plug ignition system. Recently, the vehicle has started throwing two oxygen sensor codes—P1131 (Bank 1) and P1151 (Bank 2)—indicating lean upstream O2 sensor readings, along with cylinder misfire codes PO303, PO304, PO305, and PO308. The car previously ran smoothly when warm but now exhibits a rough idle at all temperatures. I've spent the past two days researching this issue and am hesitant to immediately replace the O2 sensors. My understanding is that either the O2 sensors could be causing misfires or vice versa—misfires might be leading to incorrect lean readings. Is it unusual for both upstream O2 sensors on different banks to fail simultaneously? The vehicle had a minor tune-up before this, but now runs poorly regardless of temperature. I'm considering starting with spark plug replacement, but I don't understand why only specific cylinders (not all) would be affected if the issue were related to O2 sensor performance. I plan to clean the Mass Airflow Sensor (MAF) today, though I’m unsure whether that’s sufficient or if deeper diagnostics are needed. An additional note: just before the roughness began, I used an old key that wasn’t recognized by the system. The car briefly disabled itself and then restarted normally. Could this have triggered a fault in the Powertrain Anti-Theft System (PATS), leading to current misfire or sensor issues? I now see a PATS-related code: P1260 — 'Theft Detected - Engine Disabled.' Is this code still active, or is it just a historical record? Any insights into how these codes relate would be greatly appreciated. I'm mechanically experienced but am finding this issue particularly challenging and want to ensure I diagnose it correctly before proceeding with repairs.

Related fault codes

P0300P2177

Comments (4)

Anonymous 2016-09-10 15:28

O2 sensors are diagnostic indicators, not direct causes of misfires—so they don't typically cause cylinder misfiring. The lean readings (P1131/P1151) may be a symptom of underlying issues like fuel delivery or vacuum leaks. Start with a fuel pressure test and inspect for vacuum leaks. If the vehicle starts and runs normally without any Pats-related errors, it's unlikely that PATS is directly causing misfires. PATS anti-theft system can trigger temporary disengagement, but if the engine is now running properly, this suggests the issue may have been a transient event rather than an ongoing fault.

Anonymous 2016-09-10 15:54

Thanks for the clarification! I did not realize P1260 was still active. The code indicates that the PATS system detected a theft attempt, but since the engine is now running and no current faults are present, it's likely just a historical record. However, if the vehicle has been re-entered with a valid key or the system hasn't fully reset, this could affect sensor calibration or fuel trim settings—worth checking during diagnostics.

Anonymous 2016-09-11 06:32

Agreed—the engine is not disabled, so PATS-related issues are likely not the root cause. Have you cleaned the Mass Airflow Sensor (MAF)? Avoid using oiled air filters as they can interfere with airflow readings. Confirm there are no exhaust leaks—these can cause lean conditions and trigger O2 sensor codes. Also recommend checking fuel pressure and inspecting for vacuum leaks, especially around intake hoses and manifold gaskets.

Anonymous 2016-09-11 09:33

Thank you so much for the detailed guidance! I appreciate your help immensely. I will clean the MAF today using proper procedures—no oiled filters, just a stock Motorcraft air filter (which is nearly new). I’ve done many repairs on this vehicle before, but this one feels especially complex. I’ll systematically check for exhaust and vacuum leaks and perform a fuel pressure test as suggested. Once I complete these steps, I’ll follow your recommendations closely to identify the root cause. I’d love to stay in touch and learn more about diagnosing these issues on older 4.6L engines.