Make it buzz.

The frequency valve is controlled by the lambda control computer. It is powered by the OVP relay. If the valve isn't buzzing the chances are that the OVP relay is dead. On that SL it is difficult to get to. It is in the relay cluster above and to the right of the passengers feet. It is usually purple or some color other than silver as the rest of the relays are. It doesn't have an external fuse as the later OVP relays did.


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Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician