Sonata GL V6-3.0L (1997)
Technical Service Bulletin # 97-36-004
Date: 971201
Oxygen Sensor- Operation/Diagnosis
Group: ENGINE ELECTRICAL
Number: 97-36-004
Date: DECEMBER, 1997
Model: ALL OBD-II VEHICLES
Subject
OXYGEN SENSOR DIAGNOSIS
Description
An oxygen sensor measures the amount of oxygen present in the exhaust gas. The oxygen sensor "element is coated with a catalyst metal that produces a
small voltage from 0 to 1.00 volt at temperatures in the range of 600°F (315°F) when exposed to oxygen. The "stoichiometric" air4uel mixture for
optimum fuel economy and emissions occurs at approximately 0.50 V. When the oxygen sensor output signal is above 0.50 V, the air-fuel mixture is
considered rich and when the signal is under 0.50 V it is considered lean.
Hyundai OBD II engine management systems (1996 and later models) include two heated oxygen sensors (heated oxygen sensors allow the vehicle to go
into closed loop in 20 to 30 seconds to reduce emissions):
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The "upstream" (front) oxygen sensor is located in the exhaust stream before the catalytic converter. The front sensor provides feedback to the PCM
that is used to identify if the air-fuel mixture supplied to the cylinders is rich or lean. Under normal operating conditions, the front oxygen sensor
signal will fluctuate from 0 to 1.00 V. The front sensor signal should fluctuate, crossing the 0.50 V center about seven times in 5 seconds with the
engine held at a steady 2500 rpm, when the vehicle is at operating temperature (the signals cannot be seen when viewing with the scan tool because
the scan tool's refresh rate is not fast enough; Hyundai Diagnostic System (HDS) can be used (see "HDS Testing Procedure" in this TSB)).
-
The "downstream" (rear) oxygen sensor is located after the catalytic converter in the exhaust stream. The rear sensor provides feedback to the PCM
to "fine tune" the air-fuel ratio and to monitor catalytic converter efficiency. The rear sensor signal will also fluctuate in the 0 to 1.00 V range but the
pattern is less predictable than for the front oxygen sensor because of its position in the exhaust system. Once the catalyst has reached operating
temperature, the rear sensor signal should change very little, if at all. If the rear sensor signal fluctuates at approximately the frequency of the front
sensor, it is an indication that the catalytic converter is not at operating temperature or is malfunctioning.
Oxygen Sensor Diagnosis
A properly operating oxygen sensor may have unusual signal characteristics that are the result of other components. A malfunction of any of the
following components may affect sensor signal characteristics:
^
Fuel injector(s)
^
Air flow sensor
^
Evaporative emission system
^
Intake air temperature sensor
^
Barometric pressure sensor
^
Engine coolant temperature sensor
^
Throttle position sensor
^
Intake system (vacuum) leaks
^
Low battery charge
^
Spark plugs
The PCM does not monitor either oxygen sensor signal when the engine management system is in open loop or when the purge solenoid is operating.
If codes other than oxygen sensor codes are present, diagnose/repair these conditions BEFORE continuing with oxygen sensor diagnosis.*
Note:
* A malfunctioning front oxygen sensor may cause fuel trim codes to set.
