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Jim Grant's Tech Tips
‘95 Blazer
S/T, Oxygen Sensor Grief
Q: I am a service technician at a tire store
and would like some information on a certain vehicle. The vehicle is a
‘95 S/T Blazer, and the complaint was the "Service Engine Soon" light
was on steady. I performed the OBD system check to come to realize a code
set, a P0134 code. A fellow co-worker suggested that he had the same problem
with his ‘95 Blazer and the fault was with the EGR valve, so I serviced
the EGR valve. This did not correct the condition. I had performed the
Flow chart tests and come to realize that there was nothing wrong with
the sensor or maybe it is intermittent. I had suggested for the customer
to go to the dealer. I would like to know if you have any information
in this area? Your response would be greatly appreciated.
A: I’m
not really sure why you are servicing the Exhaust Gas Recirculation (EGR)
valve when the Diagnostic Trouble Code (DTC) P0134 is for a fault in the
Heated Oxygen sensor circuit. The simplest description for an Oxygen sensor,
is a sensor that is mounted in the exhaust, which creates a signal that
is used by the vehicle’s computer to determine if the engine is getting
the right amount of fuel to run clean and efficient. This oxygen sensor
has a little problem, it won’t create a signal if it’s temperature is
below 600 degrees Fahrenheit. During cold start-up or prolonged idling
there is not enough heat to make or keep the sensor working. A heating
element is designed into the sensor to get it quickly up to, and aid in,
maintaining operating temperature under these conditions. Today’s vehicle
computers are sharp enough to figure out that there is a problem (but
don’t give them too much credit, they’re still dumb and are easily confused)
and will turn on the "Service Engine Soon" light to alert you to a problem.
That’s the easy part! The fun begins in proving that the problem truly
exits where the computer says it does, then proving that the offending
sensor or electrical circuit is at fault.
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