P0420

Symptom: The CHECK ENGINE lamp (MIL) is on

P0420

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 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 30-100 km/h

•	Open throttle

•	Engine speed (rpm) x load (kPa) = 60 000-120 000

•	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

. Intermittent faults may occur as a result of occasional short circuits and breaks in the wiring. Jiggle the leads and in-line connectors at several places and in different directions to reveal faults in the wiring harness. Observe the multimeter, ISAT scan tool or test lamp while carrying out this check.

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 at a steady throttle opening at 40-90 km/h for 4 minutes (select a gear so that engine speed is 2000-3000 rpm). Since throttle position changes should be avoided, as level a road as possible should be chosen for this test.

-	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 the diagnostic trouble code recurred?

yes

Proceed to .

no

The remedial measure taken was correct.