P0420

THREE WAY CATALYTIC CONVERTER





Symptom Of Fault.
The CHECK ENGINE lamp (MIL) is on.

Conditions.
Diagnosis not yet performed this trip

Heating Of The Three Way Catalytic Converter:
^ Vehicle speed > 0 mph (> 0 km/h)
^ Open throttle
^ Engine speed (rpm) x load (kPa) = > 60,000
^ Aggregate acceleration > 15 sec.
^ Above conditions fulfilled for 120 sec.

Evaluation Of The Three Way Catalytic Converter:
^ Speed 19-62 mph (30-100 km/h).
^ Open throttle
^ Engine speed (rpm) x load (kPa) = 60,000 to 260,000
^ Coolant temperature > 60°C (> 140°F)
^ Rear heated oxygen sensor > 0.4 V at any time in this driving cycle.
Rear heated oxygen sensor voltage changes are corrected in regard to engine load and rpm and totalled in a measurement window determined by the front heated oxygen sensor. If the total exceeds a calibrated value, the fault criteria are satisfied.

Diagnostic Help.
A temporary or permanent decrease in the capacity of the three way catalytic converter may be caused by:
^ leaded fuel or fuel with a sulphur content.
^ fuel additives.
^ additives in the motor oil if oil consumption is abnormal.





Diagnostic Procedure.
1. Check the exhaust system
- Start the engine and run it at idling speed.
- Check the exhaust system for leakage between the engine and the rear heated oxygen sensor.

Any leakage?
YES:
^ Rectify the fault and proceed to point 4.
NO:
^ Continue with point 2.





2. Check the rear heated oxygen sensor's cable
- Inspect the cable visually for chafing of the insulation or loose contacts in the connector.

Is the cable OK?
YES:
^ Change the three way catalytic converter and continue with point 3.
NO:
^ Rectify the fault and proceed to point 4.

3. Check the fuel system .
- Check the fuel pressure and fuel pump delivery flow.

All OK?
YES:
^ continue with point 4.
NO:
^ Rectify the fault and then continue with point 4.





4. Final check:
- Clear the diagnostic trouble code.
- Implementation of driving cycle:
^ Drive the car at varying engine loads and rpm until the temperature of the coolant reaches 60°C (140°F), or for at least 5 minutes if this temperature is reached earlier.
Drive the car with a steady throttle opening at 25-56 mph (40-90 km/h) for 4 minutes (select a gear that will keep engine speed at 2000-3000rpm).
^ Since throttle position changes should be avoided, as level a road as possible should be chosen.
- Evaluation of the driving cycle:
- Connect an ISAT scan tool.
- Select "READ ON/OFF".
- Select "DIAGNOSTIC STATUS".
- Select "CATALYTIC CONVERTER".

Does the ISAT scan tool show "NOT READY"?
YES:
^ Repeat the driving cycle.
NO:
^ Check whether the diagnostic trouble code has recurred.

Has it recurred?
YES:
^ Proceed at "Before Replacing a Control Module". Component Tests and General Diagnostics
No:
^ The remedial measure taken was correct.