P0420
DTC P0420 CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD (BANK 1)Component Location:
GENERAL DESCRIPTION
The PCM uses dual oxygen sensors to monitor the efficiency of the manifold catalytic converter (warm-up catalytic converter). By monitoring the oxygen storage capacity of a catalyst, its efficiency can be indirectly calculated. The upstream (front) HO2S is used to detect the amount of oxygen in the exhaust gas before it enters the catalytic convertor. A low voltage indicates high oxygen contents (lean air mixture). A high voltage indicates low oxygen contents (rich air mixture). When the catalyst efficiency drops, no chemical reaction takes place. This means the concentration of oxygen will be the same at the rear as it is at the front. The output voltage of the rear HO2S copies the voltage of the front HO2S.To monitor the system, the lean-to-rich switches of the front HO2S to the rear HO2S is counted. The ratio of rear switches to front switches is used to determine whether the catalyst is operating properly. An effective catalyst will have fewer rear switches than front switches, that is, a ratio closer to zero.
DTC DESCRIPTION
The PCM calculates oscillation size of rear HO2S signal which represents catalyst conversion properties. This oscillation size will determine if catalyst conversion is low due to aging or poisoning from leaded fuel or misfiring. The PCM sets P0420 if the average of calculated oscillation size of rear HO2S signal during predetermined duration is higher than the predetermined threshold. If same error code is set in the next driving cycle, the PCM illuminates the MIL.
DTC Detecting Condition:
NOTE: If any codes relating to Oxygen (HO2S) sensor MAP, injector, a P2096, P2097 are present, do all repairs associated with them before proceeding with this troubleshooting procedure.
Specification:
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 0 should be below 0.2 V.
3. The switching time marked � from lean to rich should be within 2OOms,if longer than 200 ms HO2S may be not good.
4. The switching time marked 03 from rich to lean should be within 3OOms,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 regulator 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.
The amplitude of the signal output of the rear HO2S is small compared to the front HO2S because the rear HO2S detects emission gas purified by the catalytic converter. This is the normal signal waveform of the rear HO2S at idle.
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: If the wave form of rear HO2S looks similar to that of front HO2S, catalytic converter may be broken.
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 Repair" 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. Start engine and warm up to operating temperature.
2. Measure waveform between terminal 2 (up, down) of sensor harness connector and chassis ground.
Specification : For Rear HO2S : Part load(Approx. 2000 rpm) 500 - 1000 mV
3. Are the signal wave forms between front and rear HO2S about the same?
YES:
- Catalytic converter faulty.
- Repair 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.
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.