Overview of Troubleshooting

To determine the cause of DTC P0442, a performance test is needed. The performance test uses a mechanical vacuum gauge and scan tool (MB991502) set on the fuel tank differential pressure sensor (TANK PRES SNER 73). The mechanical gauge reading is used to verify scan tool (MB991502) reading. A comparison of the mechanical gauge to the scan tool determines the problem in the system.
Prior to doing the performance test, several simple inspections are needed to exclude some possibilities of the symptom.