december2022 - A11

an exhaust restriction resulting from a
melted or broken substrate? Do you hear
any rattling noises coming from the area
of the converter?
Next, a scan tool check. First to verify
the presence of the P0420 and/or P0430
DTCs but to also check for any others that
might be recorded in the ECM. Any DTC
or condition that increases emissions or
affects sensor readings can cause a converter
to fail the ECM tests even if the
converter is good. Correct all other DTCs
first and allow the Catalytic Converter
monitor to run again before proceeding.
While the scan tool is connected,
review the fuel trim data PIDs. Do they
indicate a system lean or rich condition?
If the vehicle is equipped with dual exhaust
and dual converters, is one bank skewed
lean while the other is skewed rich?
If the vehicle uses a conventional
oxygen sensor upstream of the converter,
graph and compare the signals from
the upstream and downstream sensors.
Most ECMs rely on this data to assess
the condition of the converter. The front
sensor should switch normally while
the rear sensor should remain relatively
steady. If it, too, fluctuates the same as
the front sensor, it is an indication that
the converter has failed OR the converter
has not started working, also known as
" lighting off " , because of an emissions
problem with the engine.
Vehicles using Wide Band Air Fuel
Sensors use a different diagnostic strategy
so take advantage of what the data Mode
$06 has to offer to help in your diagnosis.
Next, put the vehicle up in the air
and inspect the exhaust system and
converters for damage or obvious leaks.
Common sources of air leaks into the
exhaust that can skew the ECM's tests
are damaged flex pipes and stripped or
damaged sensor threads.
A smoke machine, especially one
that can adjust the amount of pressure
delivered, is one way to find elusive leaks.
The use of an ultrasound tool like this
Graph and compare the signals from the
upstream and downstream O2 sensors.
is another way to locate leaks that you
can't visually see. Another simple way to
check the exhaust is to connect your shop
vacuum cleaner to the exhaust, moving
the hose to the outlet side and turning it
on. Seal the hose to the exhaust and use
a soapy water solution to check for leaks.
After a quick visual, you can use a
thermal imaging camera to " see " the converter
in action.
Start the engine and allow it to reach
operating temperature and check the temperature
of the converter's front weld ring.
When using a five-gas analyzer, keep
in mind that:
* High HC emissions indicate unburned
fuel.
* High CO levels indicate partially
burnt fuel or oil.
* High NOx levels are normally caused
by high combustion temperatures and
pressures, slightly lean air/fuel mixture,
and excessively advanced ignition
timing.
Tailpipe emissions readings low in HC
and CO levels with high NOx emissions
are typically not caused by a defective converter.
The low HC and CO readings indicate
that the converter is functioning. The
root cause of the problem is an engine that
is emitting excessively high NOx emissions,
which in turn are caused by excessive
combustion chamber temperatures.
Any cylinder that is not working
as hard as the others is the most likely
cause of emissions issues. Most professional
scan tools can accurately perform
a cylinder balance test by dropping one
cylinder at a time.
You can also use the thermal imager
Even slight variations in the air/fuel
mixture will cause the converter temperature to
rise significantly.
to check cylinder power balance. Look for
cylinders that are running hotter or colder
than the others. Once identified, you can
focus your attention on the odd man out.
Remember, diagnosing Catalytic
Converter Efficiency Below Threshold
DTCs requires you to do two things. First,
determine the actual condition of your
customer's converter, and second, determine
what caused it to go bad in the first
place, OR if the converter is good, determine
what caused the ECM test to fail.
If you don't take the time to correct
Low HC and CO levels with high NOx emissions
are typically not caused by a defective converter.
the true cause, you'll only set yourself up
for a dissatisfied customer and an expensive
comeback.
VehicleServicePros.com DECEMBER 2022 11
http://www.VehicleServicePros.com

december2022

Table of Contents for the Digital Edition of december2022

Editor's Note: The technician shortage is getting real
Sneak Peek
Most Wanted
Electric vehicles - coming to a shop near you
In Focus
Diagnostic Tech: Using digital tools to reduce the friction of running a shop
Show Me Your Truck: 'Look at that Bad Larry!'
Go Sell Something: Writing a sales pitch
Driving Sales
Tales From the Road: An entrepreneurial spirit
SEMA/AAPEX Wrap-up
Diagnosing Progress
Common diagnostics and trends in hybrid and electric vehicles
Diagnosing faults on modern vehicles
The real cause of P0420/P0430 DTCs
How diagnostic tools cut through the ADAS confusion
When the tools become the tutor
Diagnostic products
december2022 - 1
december2022 - 2
december2022 - 3
december2022 - Editor's Note: The technician shortage is getting real
december2022 - 5
december2022 - Sneak Peek
december2022 - 7
december2022 - 8
december2022 - 9
december2022 - 10
december2022 - 11
december2022 - Most Wanted
december2022 - 13
december2022 - Electric vehicles - coming to a shop near you
december2022 - 15
december2022 - 16
december2022 - 17
december2022 - 18
december2022 - 19
december2022 - 20
december2022 - 21
december2022 - In Focus
december2022 - 23
december2022 - 24
december2022 - 25
december2022 - Diagnostic Tech: Using digital tools to reduce the friction of running a shop
december2022 - 27
december2022 - 28
december2022 - 29
december2022 - Show Me Your Truck: 'Look at that Bad Larry!'
december2022 - 31
december2022 - Go Sell Something: Writing a sales pitch
december2022 - 33
december2022 - 34
december2022 - Driving Sales
december2022 - 36
december2022 - 37
december2022 - Tales From the Road: An entrepreneurial spirit
december2022 - 39
december2022 - SEMA/AAPEX Wrap-up
december2022 - 41
december2022 - 42
december2022 - 43
december2022 - 44
december2022 - A1
december2022 - A2
december2022 - A3
december2022 - Diagnosing Progress
december2022 - A5
december2022 - Common diagnostics and trends in hybrid and electric vehicles
december2022 - A7
december2022 - Diagnosing faults on modern vehicles
december2022 - A9
december2022 - The real cause of P0420/P0430 DTCs
december2022 - A11
december2022 - How diagnostic tools cut through the ADAS confusion
december2022 - A13
december2022 - A14
december2022 - A15
december2022 - When the tools become the tutor
december2022 - A17
december2022 - A18
december2022 - A19
december2022 - A20
december2022 - Diagnostic products
december2022 - A22
december2022 - A23
december2022 - A24
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