Improper Diagnosis Of Catalytic Converter Failure When DTC P0420 Is Present. (TS 29 09071)

IMPROPER DIAGNOSIS OF CATALYTIC CONVERTER FAILURE WHEN DTC P0420 IS PRESENT.

TECHNICAL SERVICE BULLETIN

CONDITION

Catalytic Converters are being replaced unnecessarily under warranty and customer pay. When the warranty return Catalytic Converters are evaluated at A.S.M.C., the majority are passing the P0420 diagnostic test.

CAUSE

Technicians must follow the comprehensive diagnostic process as outlined in the Suzuki Service Manuals.

CORRECTION

DO NOT replace the Catalytic Converter assembly purely based on the fact that the DTC P0420 is present, especially if there are additional codes stored. The P0420 Service Manual procedure, when followed, requires that a significant number of DTC's, when present, must be addressed and corrected prior to confirming the P0420 failure remains, and only then can it be properly diagnosed and tested.

Part Number	Description	Qty.	Notes
14190-85Z10	Pipe, Exhaust No.1	1	Referred to in the Service Manual as the Three-Way Catalytic Convertor (TWC)

KEYS TO A SUCCESSFUL DIAGNOSIS

1. Read and follow the Service Manual section for "DTC P0420: Catalyst System Low Efficiency".  Please see the example attached from the 2006 Forenza/Reno Service Manual.
2. Familiarize yourself with the "Conditions for Setting the DTC"  which must be met for the system to set the DTC (shown at the right").
3. Operate the vehicle within the "Conditions for Setting the DTC"  and observe the Tech 2 scan tool to confirm the readiness test completes. If the test does not run or fails to complete, to improve the consistency and success of completing the readiness test, please follow the "road test" process outlined below to ensure that the required conditions are met. The idle conditions suggested will help reduce the occurrence of interruptions once the detection sequence begins.

   Conditions for Setting the DTC 

   • EWMA Oxygen storage time is greater than 2 seconds.
   • Engine run time is greater than 570 seconds.
   • Airflow is between 2.25 and 6.5 g/s.
   • Throttle position is less than 1.5015%.
   • Engine Coolant Temperature (ECT) is between 70°C (158°F) and 105°C (221°F).
   • Ambient temperature is between -7°C (- 19.4°F) and 105°C (221°F).
   • Barometric Pressure (BARO) is greater than 72 kPa (10.4 psi).
   • Closed loop enabled.
   • Catalyst temperature is between 300°C (572°F) and 975°C (1,787°F).
   • Closed loop integrator change is less than 0.03.
   • Idle time is less than 75 seconds.

   Vehicle speed is less than 3 km/h (1.9 mph).

   "Road Test" 

   • After correcting and clearing any DTC's that were stored with the P0420, connect the Tech 2 scan tool and confirm that the Readiness Tests are also reset and indicate "Incomplete"
   • Start and drive the vehicle until it reaches operating temperature (approximately 5 minutes)
   • Continue driving the vehicle at steady speeds of 40 MPH or greater for an additional 5-10 minutes.
   • Find a suitable place to pull the vehicle off the road and bring it to a safe parking place.
   • Keep the engine running at idle, and in gear for vehicles with automatic transmissions, shift manual transmissions into "Neutral".
   • Set the parking brake and shut off the A/C, lights, wipers, and any other accessories that are running, that may affect engine load.
   • Again monitor the Tech 2 readiness display looking for the "O2 Sensor" to indicate "Complete/Passed"
4. If the Readiness Test for the Catalyst has been completed and there is no current or pending P0420 DTC stored, the catalytic converter is not defective and should not be replaced. If any DTC is set, correct and clear the code and repeat Step #3.
5. If the P0420 DTC is stored continue on to item #6 and proceed with further troubleshooting and diagnosis to determine the condition of the catalyst.
6. Ensure that all  items called out in the "Test Description" section of the procedure are completed prior to beginning the "Troubleshooting" portion or the findings may be falsely influenced, resulting in an incorrect diagnosis.

   Test Description 

   Number(s) below refer to the step number(s) on the Diagnostic Table.

   1. The On-Board Diagnostic (OBD II) System Check prompts the technician to complete some basic checks and to store the Freeze Frame and Failure Records data on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information is then stored on the scan tool for later reference.
   2. If any component DTC's are set, diagnose those DTC's first. A fault in a component can cause the converter to appear degraded or may have caused its failure. 
   3. This step includes checks for conditions that can cause the three-way catalytic converter to appear degraded. Repair any problems found before proceeding with this table. 
   4. If the three-way catalytic converter needs to be replaced, make sure that another condition is not present which would cause the converter to become damaged. These conditions may include the following: misfire, high engine oil or coolant consumption, and/or retarded spark timing or weak spark. To avoid damaging the replacement converter, correct any possible causes of converter damage before replacing the catalytic converter.
   5. Clearing DTC's allows the catalyst test to be run up to 6 times this ignition cycle. Once the ignition is cycled, the test will run only once. Driving the vehicle heats the catalyst to a test temperature. The ECM must see predetermined amount of time at above idle before allowing the catalyst test to run at idle. Once at idle, the ECM will allow the system to stabilize and then test the catalyst in 2 stages. 
   6. If no faults have been found at this point and no additional DTC's were set, refer to [Diagnostic Aids]  for additional checks and information.