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2002 Buick LeSabre 3800 Engine Hesitation with P0131 O2 Sensor Code - Diagnosis and Fix

Model: 2002 Buick LeSabre Fault Code: P0131 Posted: 2008-05-13 15:00

I've been struggling with a persistent engine hesitation issue on my 2002 Buick LeSabre 3800 for approximately four months. The vehicle hesitates when starting from a stop—whether cold or hot—and responds sluggishly to throttle inputs, giving the impression it's starving for fuel. Previously, I noticed a lean oxygen sensor code (P0131), but that has since disappeared after recent repairs. Here’s what I’ve already done: - Complete tune-up and replacement of both O2 sensors - Replaced the entire exhaust system (covered under GM 80K emissions warranty; original catalytic converter was clogged) - Performed injector service - Installed new O2 sensors, which ran for about two weeks before a new converter was installed Diagnostic checks: - Fuel pressure test: 55 PSI at KOEO, 46–48 PSI at KOER — within normal range - No vacuum leaks detected during inspection - Ignition Control Module tested and found to be functioning properly A battery issue occurred about three weeks ago—initially sluggish starts. Upon testing, the battery was severely degraded with a rotted-out positive terminal (a known issue with AC Delco batteries). My current theory: The problem may stem from one or more of these sources: - Intake plenum leak - ECU damage due to voltage spike from the battery failure - Weak fuel pump performance I’m seeking input on whether I’ve missed any key diagnostics. Any insights would be greatly appreciated. Thank you, Joe

Related fault codes
P0131
Comments (7)
Anonymous 2008-05-14 13:32

The ECU is likely unaffected by the battery issue, as voltage spikes typically don’t damage it directly. However, double-check for vacuum leaks—especially in the intake plenum or intake manifold. Leaks near the injectors can cause misfires and hesitation. Additionally, if your 2002 Buick LeSabre has an EGR valve, remove it and inspect its operation. Check for blockages or damage in the EGR passages; air leakage into internal EGR paths may lead to erratic idle behavior. Please update with your findings.

Anonymous 2008-05-14 23:16

Thanks for the advice—I’ll reinspect the vacuum system and check the EGR valve. However, I’ve confirmed that symptoms only appear during acceleration (e.g., when taking off from a stop or accelerating through traffic), not at idle. I’ll verify all your suggestions and post results once completed.

Anonymous 2008-05-15 05:05

Has the catalytic converter been reinstalled and properly secured after replacement? Ensure it’s fully plugged in and functioning correctly.

Anonymous 2008-05-15 08:34

Thanks for asking—no, the issue persisted even within the first mile of driving after the converter was replaced. The dealership performed a full system rebuild from the intake manifold back. Initially, I thought this would resolve it, but it didn’t. I’m now considering whether the O2 sensors may have been damaged again during the two-week gap between their replacement and the converter installation. Is that a plausible scenario?

Anonymous 2008-05-15 15:51

Is your vehicle equipped with a Mass Airflow (MAF) sensor or a Manifold Absolute Pressure (MAP) sensor? What does your scan tool show for fuel trims and oxygen sensor readings? Check if fuel pressure is stable under load. Some 2002 Buick LeSabre 3800 models have known issues with clogged injectors or intake gaskets—verify these components. Also, clean the throttle body and inspect the EGR port. A proper O2 sensor scope reading is essential to confirm actual sensor behavior.

Anonymous 2012-01-08 07:16

Check each spark plug coil individually by removing the ignition wire and testing for spark. A weak or missing spark can cause hesitation during acceleration.

Anonymous 2012-01-08 12:43

Thank you all for your helpful input. The issue has now been resolved—the root cause was a loose wiring connection in the MAF sensor harness. After securing the wire, the engine runs smoothly and responds instantly to throttle inputs, like a kitten again.