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2003 Buick Park Avenue P0172 Bank 1 Rich Code: Diagnosis and Next Steps

Model: 2003 Buick Park Avenue Fault Code: P0172 Posted: 2019-03-07 08:02

My 2003 Buick Park Avenue has a stored P0172 code indicating a rich condition in Bank 1. The MIL is illuminated, but the engine starts and runs smoothly with no misfires or vacuum leaks. I've checked the air filter and air box—no restrictions found—and fuel pressure appears normal. The car performs well under all conditions. What should I check next to resolve this issue? Any guidance on troubleshooting would be greatly appreciated.

Related fault codes
P0172
Comments (6)
Anonymous 2019-03-07 11:26

https://www.obd-codes.com/p0172

Anonymous 2019-03-08 09:25

Restricted airflow affects both fuel banks. The PCM is detecting a rich condition in Bank 1. Increased fuel pressure would impact both banks. I suspect leaking fuel injectors. Does the engine start smoothly when hot? Check for oil contamination or fuel smell. Do you have an OBD-II scanner or code reader available?

Anonymous 2019-03-08 10:23

Also, remove the vacuum hose from the fuel pressure regulator and run the engine for several minutes. Observe if fuel leaks out—this could indicate a ruptured regulator. A failed regulator affects both banks but may trigger additional codes on the other bank. Use a scan tool to check short-term and long-term fuel trims at various RPMs (idle, 1500, 2500, 3500). Consider using a Techtron Total Fuel Cleaner as a potential remedy.

Anonymous 2019-03-08 12:37

The engine starts fine and does not produce black smoke or noticeable exhaust emissions.

Anonymous 2019-03-09 08:42

What is the behavior of your oxygen sensor at idle? Does it switch between 200 mV and 800 mV? A faulty O2 sensor can send incorrect signals to the PCM, leading the system to incorrectly adjust fuel mixture—either too lean or too rich. Monitor both short-term and long-term fuel trims across different RPMs (idle, 1500, 2500, 3500). Without scan tool data, diagnosis is limited. You may need to backprobe the O2 sensor signal wire with a digital multimeter. Have you tested or replaced the fuel pressure regulator?

Anonymous 2019-03-09 08:49

I've also seen cases where a faulty MAF (Mass Airflow) sensor causes a rich condition at idle, especially in older vehicles like this model.