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COMPONENT LOCATION

GENERAL DESCRIPTION

The ECM 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 converter. 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 ECM 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 ECM sets P0420 if the average of calculated oscillation size of rear HO2S signal during predetermined duration is higher than the predetermined threshold.

DTC DETECTING CONDITION

Item	Detecting Condition	Possible Cause
DTC Strategy	● Check catalyst oxygen storage capacity by evaluation downstream O2 sensor fluctuations	● Exhaust gas leaks ● Faulty rear HO2S ● Faulty three way catalyst converter
Enable Conditions	● Coolant temperature ＞74℃(165℉) ● 5 ＜ Vehicle speed(km/h) ＜ 180 ● Engine speed ＜ 3400rpm ● 200 ＜ Mass air flow(mg/rev.) ＜700 ● Canister load = 0.5 ● 400℃(752℉) ≤ Catalyst temp. model ≤ 900℃(1652℉) ● Lambda control active ＆ Stable driving condition ● Downstream O2 sensor operative readiness ● No opening / closing of Canister Purge Valve ● No relevant failure ● 11V ＜ Battery voltage ＜ 16V
Threshold Value	● Average malfunction index ＞ 0.3
Diagnostic Time	● 50 Lambda controller Cycles
MIL On Condition	● 2 Driving Cycles

SIGNAL WAVEFROM AND DATA

Test Condition		Scan Tool Parameter
Test Condition		O2 SNSR VOL.-B1/S1	Scan Tool Parameter
Normal Value when circuit is normal	Idle after warm up	Signal is switching from rich(above 0.45V) to lean(below 0.45V) a minimum of 3 times in 10 seconds.	above 0.7V
HO2S(B1S1) signal circuit open		Approx. 0.43~0.45V	-
HO2S(B1S2) signal circuit open		-	Approx. 0.43~0.45V

note

If any codes relating to injectors, HO2S, ECT(Engine Coolant Temperature)Sensor, Throttle Position sensor or Mass Air Flow Sensor are stored, do ALL REPAIRS associated with those codes before proceeding with this troubleshooting tree.

MONITOR DTC STATUS

Connect scan tool and select "Diagnostic Trouble Codes(DTCs)" mode

Press F4(DTAL) to select DTC information from the DTCs menu

Confirm that "DTC Readiness Flag" indicates "Complete". If not, drive the vehicle within conditions noted in the freeze frame data or enable conditions

Read "DTC Status" parameter

Is parameter displayed "History(Not Present) fault"?

note

History (Not Present) fault : DTC occurred but has been cleared.

Present fault : DTC is occurring at present time.

▶ Fault is intermittent caused by poor contact in the sensor's and/or ECM's connector or was repaired and ECM 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.

▶ Go to next step as below.

EXHAUST SYSTEM INSPECTION

Visually/physically inspect the following conditions:

Exhaust system between HO2S and Three way catalyst for air leakage, restriction and damage.

Damage, and for loose or missing hardware:

Was a problem found in any of the above areas?

▶ Repair as necessary and go to "Verification of Vehicle Repair" procedure

▶ Go to "Rear HO2S Inspection " procedure

REAR HO2S INSPECTION

Visually/physically inspect the rear HO2S for the following conditions:

Ensure that the HO2S is securely installed.(Pigtail and wiring harness not making contact with the exhaust pipe)

Check for corrosion on terminals

Check for terminal tension ( at the HO2S and at the ECM)

Any road damage

Was a problem found in any of the above areas?

▶ Repair as necessary and go to "Verification of Vehicle Repair" procedure

▶ Go to "TWC Inspection " procedure

TWC INSPECTION

Visually/physically inspect the three-way catalyst(TWC) converter for the following damage:

Severe discoloration caused by excessive temperature

Dents and holes

Internal rattle caused by a damaged catalyst

Also, ensure that the TWC is a proper original equipment manufacturer part.

Was a problem found?

▶ Replace TWC and go to "Verification of Vehicle Repair" procedure

▶ Check for poor connection between ECM and component: backed out terminal, improper mating, broken locks or poor terminal to wire connection. Repair as necessary and 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.

Connect scan tool and select "Diagnostic Trouble Codes(DTCs)" mode.

Press F4(DTAL) and confirm that "DTC Readiness Flag" indicates "Complete". If not, drive the vehicle within conditions noted in the freeze frame data or enable conditions.

Read "DTC Status" parameter.

Is parameter displayed "History(Not Present) fault"?

▶ System performing to specification at this time. Clear the DTC

▶ Go to the applicable troubleshooting procedure.