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2002 Mercury Sable LS O2 Sensor Replacement Failed: P1131, P1151, P0401 Codes After Installation

Model: 2002 Mercury Sable LS Fault Code: P0401 Posted: 2016-01-19 17:11

I recently replaced both the downstream and upstream oxygen (O2) sensors on my 2002 Mercury Sable LS. After the replacement, my vehicle now shows three diagnostic trouble codes: P1131, P1151, and P0401. My handheld OBD-II scanner displays these codes, along with an undefined code that does not appear to be readable. I am concerned because this is a significant number of issues for a vehicle with only basic plug-in diagnostics. The presence of both P1131 and P1151 suggests a lean condition in Bank 1 and Bank 2, while P0401 (Pending) indicates insufficient exhaust gas flow — which may be related to the oxygen sensor readings or underlying engine performance issues.

Related fault codes

P0401P1131P1151

Comments (2)

Anonymous 2016-01-19 17:32

I'm now seeing 'insufficient exhaust gas flow' along with P1131, P1151, and P0401 — that's an unusually high number of codes for a 2002 Mercury Sable LS. I've never encountered this before. My scanner is just a basic plug-in device. I need help diagnosing this issue quickly and affordably.

Anonymous 2016-01-20 08:29

These are the only active codes: P1131 and P1151 — both related to Bank 1 and Bank 2, indicating a lean mixture condition. Vacuum leaks are one of the most common causes. Check for any loose or damaged hoses, especially around the intake manifold. P0401 (Pending) is directly linked to this issue and may be contributing to the lean readings. It indicates that exhaust gas flow is below expected levels — a symptom often tied to sensor inaccuracies or engine performance problems. For more details: https://www.obd-codes.com/p1151-ford, https://www.obd-codes.com/p0401