Maybe not so hard. Engine rpms are critical to the Klima relay. Engine rpms are criticla to tach operation. Engine rpms are critical to ABS and posibly un noticed, engine rpms are critical to idle speed stabilization.

The unusual thing is that diesels have no ignition so how does one get engine rpms? Turns out the OVP is critical here because it powers the EGR transducer which takes the crank sensor inducted AC pulse and converts it to a square wave DC rpm (engine speed) signal. Fix the rpm problem and you have probably fixed everything.

I would scope the induced crank signal versus eng speed signal where ever it don't work and work back to the EGR transducer or the crank sensor.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician