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Amedee, Lexus Technician
Category: Lexus
Satisfied Customers: 26432
Experience:  ASE certified tech advanced level specialist. Wisconsin certified emissions state inspector
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1997 Lexus LS400: has a check engine light..air filter, fuel filter

Resolved Question:

My 1997 Lexus LS400 has a check engine light. The code is P0171 Bank 1 System lean. I have replaced the MAF sensor, air filter, fuel filter and had a smoke test done by 2 separate shops. No vacum leaks have been found. A third tech at an auto store listended to the engine and said that there was not an apparant leak at the manifold gasket. Please help.
Submitted: 6 years ago.
Category: Lexus
Expert:  Amedee replied 6 years ago.

How does the engine run? how does it idle and accelerate?

Customer: replied 6 years ago.
Vehicle and runs runs smoothly...and accelerates in all conditions normally. I also gave it a full tune up last month with Denso parts for what it's worth.
Expert:  Amedee replied 6 years ago.
Do you know what the fuel trims are at when the engine is fully warmed up?
Customer: replied 6 years ago.

I don't know what the fuel trims are. That level of detail is beyond my ability at this point. However, the fuel pump was replaced by the Lexus dealership approximately 18 months ago.

Expert:  Amedee replied 6 years ago.
If what you are saying it true, then chances are you just have plugged or restricted fuel injectors.
Customer: replied 6 years ago.
So a fuel injector cleaning would restore the fuel/air ratio and clear the code?
Expert:  Amedee replied 6 years ago.
1. Only if the fuel injectors are plugged up.

2. it all depends on bad they are. THey may need to be replaced.

Customer: replied 6 years ago.
Could an upstream or downstream O2 sensor cause a lean code? Are they difficult to replace on the 97 LS400?
Expert:  Amedee replied 6 years ago.
YES.. it is possible and no.. they are not hard to replace.
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