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Hi, my 2002 Toyota Corolla still has the p0171 code. My mechanic replaced o2 sensors, mass airflow, cataliic converter, smoke test,changed fuel injectors and fuel pump. Did everything you guys suggested, a new mechanic double checked my car didn’t find anything. After we reset the code, sometimes don’t even get to drive it comes back immediately. Otherwise max you can drive about 10 miles. Please help
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What are your ST and LT Fuel trims reading? What are the 02 voltages on Upstream and Downstream? Could be complicated situation to diagnose however sounds like your mechanic is firing parts at it…
Did your mechanic drive test it and look at live data, or just fire the parts cannon at it? Both lean and rich codes can be caused by a number of issues, one needs to carefully analyze data to determine a probable cause of the code. Like jjohnson1 said I’d start by looking at the fuel trims and O2s, try to richen the mixture with propane and see how the O2s and trims respond. Was the smoke test done on a stone cold engine? Something like an intake gasket could seal itself as the car warms up. Any exhaust leaks?
If you take it to a shop, ask them to explain (with data) why they recommend replacing parts.
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