Engine Controls - Oxygen Sensor Function/Diagnosis
SOURCE: Hyundai Tech Net Times Volume 13 Issue 5 2003TITLE: Oxygen Sensors
APPLIES TO: 96 - 04 All
SERVICE TIP:
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�C) when exposed to oxygen. The "stoichiometric" air-fuel 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 or less to reduce emissions):
^ 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 "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 1.00V 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.
^ Several Diagnostic Trouble Codes use specific terminology to refer to sensor location. The illustration and key below explain the following terms:
^ Engine BANK Bank 1 is closer to the dash panel, (also referred to as RH or right hand). Bank 2 is closer to the radiator, (also referred to as LH or left hand).
^ UP Refers to Sensor 1 or "front sensor". It is located closer to the exhaust manifold and before the catalytic converter.
^ DOWN Refers to Sensor 2 or "rear sensor." It is located after the catalytic converter.
The following examples show how to interpret oxygen sensor terminology:
B1/S1 = Bank 1/Sensor 1 = Dash panel side, BEFORE the catalyst or "upstream"
B2/S2 = Bank 2/Sensor 2 = Radiator side, AFTER the catalyst or "downstream"
^ The Hi-Scan Pro testing procedure is provided in the following section. The Hi-Scan Pro test is a quick procedure that provides basic sensor information.
Hi-Scan Pro Testing Procedure
Connect the Hi-Scan Pro and retrieve all diagnostic codes. Record the codes and freeze frame data (if available) for later reference.
1. A. Warm up the vehicle to operating temperature (for at least 3 minutes)
B. Select vehicle, year, etc.
C. Select "Engine"
D. Select "Data"
E. After OBD II data appears press "N"
F. Select "Custom Data"
G. Select "02-B1 S1" and "02-B1 S2" (front and rear oxygen sensors) and ENG RPM if no tachometer is available.
H. Press "N" and the selected data will appear.
2. While holding the engine speed at 2500 rpm in Neutral or Park (with no load) observe the front and rear oxygen sensors for approximately one minute. The front oxygen sensor should fluctuate rapidly between 0.095 and 0.995 V. The voltage should read higher than 0.600 V several times and lower than 0.350 V several times. The voltage should never exceed 1.00 V when using the Hi-Scan Pro.
If an Accent, Elantra or Tiburon front or rear oxygen sensor reads a fixed value of 0.425 V to 0.500 V, or a rear oxygen sensor reads a fixed value of 0.425 V to 0.500 V, or a Sonata reads a fixed value of 0.010 -0.080 V, check for an open/shorted oxygen sensor circuit or no output from the sensor.
The Hi-Scan Pro can also be used to check the sensors while the vehicle is being driven. An assistant is needed to perform this procedure. Use the Hi-Scan Pro as set up in the previous test procedure.
1. While driving in first gear, accelerate so the engine speed is near 4000 rpm. Quickly release the accelerator and observe the readings from both sensors. The sensors should read lean (in the range of 0.20 V down to 0 V) on the Hi-Scan Pro due to the fuel cutoff during deceleration.
2. While driving in first gear, accelerate hard and observe both sensors. The sensors should read rich (in the range of 0.60 V to 1.0 V) on the Hi-Scan Pro.
Oxygen sensors can be monitored using HDS. The sensors can be observed using either "Custom Meters" or "Signal Wave Forms" on the HDS unit. It is preferable to use "signal Wave Forms" since the signal resolution is better with the engine operating at 2500 rpm, which is required for proper testing.
The HDS testing procedure requires a more involved set up but provides more detailed information about the sensors' performance. Refer to Technical Service Bulletin #97-36-004 for the testing procedure.
When the HDS is used to monitor oxygen sensor signals on 1996 and 1997 Accent & Elantra and 1997 Tiburon vehicles, a 0.70 V (0.71 V for Tiburon) signal offset is observed. This shifts the sensor readings 0.70 V (0.71 V for Tiburon) higher so the new signal range is 0.70 V to 1.70 V (0.71 V to 1.71 V for Tiburon). This shift is seen only when using the HDS machine because the sensor signal is read before it is processed (filtered) by the engine control module (ECM). (This offset is not present when using the Scan Tool.) The offset has no affect on the sensor signal appearance or frequency.
The oxygen sensor voltage offset (or bias voltage) observed when using the Hyundai Diagnostic System (HDS) was changed on 1998 Accent, Elantra & Tiburon from the value of previous model years. The oxygen sensor voltage offset is 0.27 volts for 1998 Elantra and Tiburon, and 0.30 volts for 1998 Accent.
Oxygen Sensor Diagnostic Trouble Codes
The list below contains specific codes for Hyundai oxygen sensors and their explanations as needed.
In addition to further information found in shop manuals, several Technical Service Bulletins have been released regarding oxygen sensors. These can be found in the TSB bound manual or at the Hyundai Service website "Webtech Pro" section, (login required.)
Keeping up to date on Hyundai oxygen sensor technology will make oxygen sensor diagnosis easier for you.