Step by step guide on how to repair automobile lean code problems, this article
pertains to most vehicles.
Difficulty Scale: 4 of 10
Tools and Supplies Needed
- Code Reader
- Wrench set
- Socket Set
- Protective gloves and eye wear
Begin with the vehicle parked on flat ground in park with the emergency brake set.
- Once a
check engine or service engine soon light
has determined a lean engine code
has materialized, a repair procedure inspection is needed. Explanation: A lean code
is enabled when the computer has detected enrichment adjustments have maxed out,
with no results, this inability triggers the lean code.
Lean Mixture Code
Step 2 - Un-metered air which enters the intake
system of the engine can cause a lean mixture code to be triggered, inspect all
vacuum lines for cracks or dilapidation. Check the integrity of vacuum hoses at
each end of the hose.
Step 3 - The intake system utilizes gaskets which
seal various components, if these gaskets fail a
will result, causing the code failure. Use carburetor cleaner to help locate
any potential leaks by spraying around gasket surfaces and observe a rise in engine
idle speed if a leak exists.
Vacuum Leak Testing
Step 4 - An exhaust leak will allow fresh air to
enter the system on the negative pressure side of an exhaust event, this will cause
to produce a lean reading. An exhaust system manages both pressure
and vacuum cycles while an engine runs. To inspect for an exhaust leak, have a helper
start the engine and hold the idle at about 1500 rpm, listen for additional exhaust
noises coming from the system including
. Also, look for black soot at any point in the system as this can
indicate an exhaust leak.
Step 5 - After miles of driving, the mass air flow
sensor's filament or hot wire, can become contaminated due air impurities which
create false readings. Using sensor safe carburetor cleaner to clean this filament
can sometimes remove these deposits allowing the sensor to obtain a correct reading.
Service Mass Air Flow Sensor MAF
Step 6 - Testing the exhaust system
can help determine the functionality of the sensor. If the sensing
element fails, feedback information will be incorrect causing a lean mixture code.
Step 7 - When an engine misfires an almost clean
charge of oxygen is released into the exhaust system. This will cause the exhaust
system to test lean as tested by the O2 sensors, this can sometimes be fixed by
a tune up
Step 8 - An air intake boot transfers engine air
from the mass air flow sensor to the throttle actuator. If the
it can cause a false reading from the mass air flow sensor producing the code.
After repairs are completed, clear the trouble codes and allow the computer monitors
to reset by driving between 20 and 40 miles to confirm correct system functionality.
Common Misconception: When an engine misfires, the cylinder runs lean, not rich,
this is because the air to fuel ratio favors air by 14x. Therefore, an engine must
be running properly without
Air Intake Boot Replacement
to avoid lean mixture codes. Optimum air to fuel mixture (14 to 1)
is called stoichiometric
which means: chemically balanced. The engine fuel management system is controlled
by the computer and various sensors which feedback data.
- Check all vacuum hoses when replacing a single failed hose.
- Check connecting hoses to such items as a breather tube or EVAP system
Article first published 2016-11-28