P0138
DTC P0138 02 SENSOR CIRCUIT HIGH INPUT (BANK 1/SENSOR 2)
GENERAL DESCRIPTION
The rear heated oxygen sensor is mounted on the rear side of the Catalytic Converter (warm-up catalytic converter) or in the rear exhaust pipe, which is able to detect the catalyst efficiency. The rear heated oxygen sensor (HO2S) produces a voltage between 0 V and 1 V. This rear heated oxygen sensor is used to estimate the oxygen storage capability. If a catalyst has good conversion properties, the oxygen fluctuations are smoothed by the oxygen storage capacity of the catalyst. If the conversion provided by the catalyst is low due to aging, poisoning or misfiring, then the oxygen fluctuations are similar to signals from the front oxygen sensor.
DTC DESCRIPTION
PCM sets DTC P0132 or P0138 if the PCM detects signal voltage higher than the possible range of a properly operating front or rear heated oxygen sensor (HO2S) respectively.
DTC Detecting Condition:
Specification:
Schematic Diagram:
SIGNAL WAVEFORM & DATA
This figures show the wave form measured at terminal 2 of HO2S at idle RPM.
1. The average voltage of HO2S should be 0.5 V.
2. When sudden decceleration,the voltage at point (1) should be below 0.2 V.
3. The switching time marked (2) from lean to rich should be within 200 ms,if longer than 200 ms HO2S may be not good.
4. The switching time marked (3) from rich to lean should be within 300 ms,if longer than 300 ms HO2S may be not good.
5. In case the average voltage of HO2S is over 0.6 V.
Possible cause: Injector_leakage,faulty Pressure regrator Faulty MAPS,ECTS.
6. The rear oxygen sensor output is usually not changeable like front oxygen sensor,however,if it moves like front oxygen sensor,the catalytic converter is broken.
If you release the accelerator pedal suddenly after engine running about 4000 rpm, fuel supply will stop for short period and the 02 sensor service data in the Hi-Scan (Pro) will display values 200 mV or lower. When you suddenly press on the accelerator pedal down, the voltage will reach 0.6-1.0 V.When you let the engine idle again, the voltage will fluctuate between 200 mV or lower and 0.6 - 1.0 V. In this case, the O2 sensor can be determined as good.
MONITOR DTC STATUS
This is the inspection procedure to determine whether it is present DTC or memoried one by monitoring the current signal or by using the function of oscilloscope with Hi-scan pro.
1. Connect scantool to Data Link Connector(DLC).
2. Warm up the engine to normal operating temperature.
3. Monitor the "HO2S signal" parameter on the scantool.
NOTE: The data shown above is only for reference and there may be a little difference actually.
Service standard For front HO2S
- When decelerating suddenly from 4000 rpm: 200 mV or less
- When engine is suddenly raced : 600 - 1000 mV
- 1500 rpm: The fluctuation between 400 mV or less and 600 - 1000 mV For Rear HO2S
- Part load(Approx 2000 rpm) 500 - 1000 mV
4. Is parameter displayed within specifications?
YES: Fault is intermittent caused by poor contact in the sensor's and/or PCM's connector or was repaired and PCM memory was not cleared.
Thoroughly check connectors for looseness, poor connection, bending, corrosion,contamination,deterioration, or damage Repair or replace as necessary and then go to "Verification of Vehicle Repar" procedure.
NO: Go to "W/Harness Inspection" procedure.
TERMINAL & CONNECTOR INSPECTION
1. Many malfunctions in the electrical system are caused by poor harness and terminals. Faults can also be caused by interference from other electrical systems, and mechanical or chemical damage.
2. Thoroughly check connectors for looseness, poor connection, bending, corrosion, contamination,deterioration, or damage.
3. Has a problem been found?
YES: Repair as necessary and go to "Verification of vehicle Repair" procedure.
NO: Go to "Signal circuit inspection" procedure.
SIGNAL CIRCUIT INSPECTION
1. Check for short to power in harness
1. Ignition "OFF'
2. Disconnect HO2S sensor connector and PCM connector.
3. Ignition "ON" & Engine "OFF"
4. Measure voltage between terminal 2 of sensor harness connector.
Specification: below 0.5 V
5. Is measure voltage within Specification?
YES: Go to "Component Inspection" procedure.
NO:
- Short circuit to battery between HO2S harness connector and PCM harness connector.
- Repair as necessary and then go to "Verification of Vehicle Repair" procedure.
NOTE: In case,when HO2S harness connector disconnected,the output voltage at terminal 2 is 12 V.
- Possible cause: Short circuit to battery in harness between E/R-J/BOX and terminal 2 of HO2S heater.
COMPONENT INSPECTION
1. Check HO2S
1. Thoroughly check HO2S for contamination,deterioration or damage.
2. Is HO2S contaminated, deteriorated or damaged?
YES: Substitute with a known-good HO2S and check for proper operation. If the problem is corrected, replace HO2S and then go to "Verification of Vehicle Repair" procedure.
NO: Go to "Check PCM" as below.
2. Check PCM
The purpose of checking PCM is to determine whether there is any malfunction of PCM.
1. Ignition "OFF"
2. Disconnect HO2S sensor connector.
3. Connect Scantool and Engine "ON"
4. Select simulation function on scantool.
5. Simulate voltage at terminal 2 of HO2S sensor signal connector.
6. Verify HO2S voltage to change while raising or lowering simulation voltage with scan tool within 0.2 - 0.8 V
Specification: If the data is changeable as simulation voltage changes, it's OK
7. Is HO2S signal value changed according to simulation voltage?
YES: Thoroughly check connectors for looseness, poor connection, bending, corrosion, contamination, deterioration or damage Repair or replace as necessary and then go to "Verification of Vehicle Repair" procedure.
NO: Substitute with a known-good PCM and check for proper operation. If the problem is corrected, replace PCM and then go to "Verification of Vehicle Repair" procedure.
NOTE: It is not permitted to check the internal resistance of HO2S with analog multimeter.
VERIFICATION OF VEHICLE REPAIR
After a repair, it is essential to verify that the fault has been corrected.
1. Monitor and record the Freeze Frame Data for the Diagnostic Trouble Code (DTC) which has been diagnosed.
2. Using a Scantool, Clear the DTCs.
3. Operate the vehicle within conditions noted in the freeze frame data or enable conditions.
4. Monitor that all rediness test have been verified as "Complete"
5. Are any DTCs present?
YES: Go to the applicable troubleshooting procedure.
NO: System is performing to specification at this time.