Re: P0171 bank 1 too lean

On 28/2/2025 1:01 pm, AMuzi wrote:

On 2/27/2025 6:45 PM, Isaac Montara wrote:

I have a Mitsubishi Lancer ES early 2000s with a P0171 that keeps coming
back after I reset it with an OBDII hand-held code reading tool.
>
I put new spark plugs in and it still sets the P0171 bank 1 too lean.
When it idles, it often kills the motor so it's not getting enough fuel I
think.
>
But I don't know cars all that well. How do I increase the idle RPM on an early 2000s Lancer ES?

 This guy covered the usual items for 'lean bank'
 PCM software needs to be updated
Vacuum leaks (Intake Manifold Gaskets, vacuum hoses, PCV hoses, etc.)
Mass Airflow Sensor (MAF)
Plugged Fuel Filter or weak Fuel Pump
Plugged or dirty Fuel Injectors
 without success but then discovered an unusual failure:
 https://www.clublexus.com/forums/rx-2nd-gen-2004-2009/671879-finally- solved-p0171-and-p0174-codes.html
 

Interesting story and there are many like this. But the dealer scan tools should have been able to test for it. Look up OBD2 Mode $08 - control operations of on-board systems. Mode $08 allows the tech to control certain operations of the EMS allowing a scan tool to do bidirectional control of an onboard system or test. Most solenoids and emission equipment can be controlled and cycled independently of conditions and commands. Factory scan tools and the more expensive aftermarket scanners offer bi-directional functionality thus have Mode $08 capabilities. This is a very handy method of testing for equipment failure without the need to wait for the EMS to command the operation. Would have been very handy for you, no need to wait out the time or an idle situation.
HTH
--
Xeno
Nothing astonishes Noddy so much as common sense and plain dealing.
       (with apologies to Ralph Waldo Emerson)