DTC P1371: Valve Lift Control Checksum Error-Above Limit: Diagnosis/Troubleshooting

Perform system test for large lift 

During the system test for large lift, the valves remain at large 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 large lift, the fault type over limit is recorded.

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

In order to ensure that the fault is repaired, 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 does not change the mixture at all given acceleration with wide-open throttle (F_R at 1) and enriches the mixture in the opposite cylinder bank (F_R > 1) see drawing below. Given a difference between F_R1 and F_R2 of more than 8 %, a fault is certainly present.

If the difference is less than 4 %, 1 valve may be faulty on both cylinder banks. In this case, all flat-base tappets of the inlet valves must be replaced.

Fig 1: P1371 Oscilloscope Pattern (Checksum Error - Above Limit)

Courtesy of PORSCHE OF NORTH AMERICA, INC.

1. Select system test.
2. Select Request large lift.

   If Valve 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.

4. Perform acceleration with wide-open throttle in 2nd gear, until Valve lift diagnosis complete appears.
   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 sensors during acceleration with wide- open throttle or to record their behaviour with the data logger.