DME 7.8

P0420

40 TWC Conversion, Bank 1 - Above Limit

Diagnosis conditions
- TWC temperature 420 - 600 °C
- 85 seconds within rpm/load range (cumulative)
- EVAP canister burden < 8
- Speed 1280 - 2440 rpm
- 20 - 40 %engine load (relative air charge)
- Oxygen sensing ahead of TWC is active
- Oxygen sensing after TWC ready for operation
- Engine starting temperature > - 20 °C
- No faults in memory

Possible fault cause
- Oxygen sensor ahead of and after TWC exchanged
- Valve lift fault
- Aged oxygen sensor after TWC
- TWC faulty

Diagnosis/troubleshooting

NOTE: If an ageing oxygen sensor is recorded in conjunction with a fault in the TWC, a check must be performed with a new oxygen sensor to see whether a TWC fault is still indicated.







Perform system test for small lift

WARNING: Test is carried out while driving. Have a second person operate the Porsche System Tester 2.

During the system test for small lift, the valves remain at small lift, regardless of the type of driving. Faulty switching conditions can be detected by rough running, just like with misfire detection. If a valve is not switched to small lift, the fault type 'under limit' is recorded.

Several cylinders may be stored as faulty, although only 1 valve on one cylinder is faulty.

In order to guarantee safety during repairs, the flat-base tappets of the inlet valves of the entire cylinder bank should be replaced if a fault occurs.

A faulty flat-base tappet can be detected because the oxygen sensor F(R) for this cylinder bank enriches the mixture (F(R) > 1) during acceleration with wide-open throttle - see drawing below. Difference from the other oxygen sensor > approx. 15 %. In the case of a fault, the flat-base tappets of the inlet valves for the entire cylinder bank must be replaced.







1 - Select system test.
2 - Select 'Request small lift'.
If "Valve lift diagnosis not ready" appears, a fault may have been stored.
1. Erase the fault memory.

3 - Activate the system test with the key [F8] immediately before acceleration with wide-open throttle.
The message "Drive link active" then appears.

NOTE: If 'Request small lift' appears, the valves remain at small lift, i.e. the performance is reduced dramatically.

4 - Perform acceleration with wide-open throttle in 2nd gear, until "Valve lift diagnosis complete" (max. 4,000 rpm) appears.
At speeds above 4,000 rpm, misfires may be stored. Delete the fault memory and repeat the test.

NOTE:
- If a fault is detected, it is only recorded in the fault memory after 6,000 ignitions (at idling speed approx. 3 minutes waiting time).
- It is important to observe the oxygen sensor during acceleration with wide-open throttle or to record its behaviour with the data logger.