Symptoms

Momentary power drops in various areas of engine operation, coupled with rattling sounds under the floor of the vehicle and loud roaring noises, often from the beginning of the mid-speed range.

Cause – throttling the exhaust gas flow in the catalytic converter

Under the influence of strong variable thermal loads, the catalyst monolith may come loose or crack in the housing and obstruct the flow of exhaust gas from time to time. The resulting abnormally high exhaust back pressure leads to a reduction in engine power. On a bumpy road, the loosening of the ceramic monolith makes itself felt by clattering and rumbling (in the medium speed range).

Troubleshooting and fault elimination

In this case, the fault memory usually does not contain any codes. If the fault does not occur during a test drive, you can drive onto the lift and tap the catalyst with your hand. Rattling inside will then be clearly audible. attention: wear gloves, because there is a risk of burns!