2004 e320 cdi w211 Have taken for engine diagnostics and had faults cleared, engine management light. Unfortunately by bad coincidence upon leaving indie steering is very heavy, indie checked tyres, belt, fluid level etc but nothing obvious. Steering remains constantly stiff at whatever speed and with front end jacked up, resistance to manually turning wheel direction is equal with engine running or not. I can hear pas pump hissing as it normally does when turning at standstill. My question is what is the most likely component to be at fault: Wheel speed sensor steering solenoid pump or rack? And how do I test them to confirm the culprit?