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Matt, Mechanical Engineer
Category: Mercedes
Satisfied Customers: 22745
Experience:  BEng hons Mech engineering, in auto industry 22 years
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My friend has a diesel Avantegarde 2003 which has been cutting

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My friend has a diesel Avantegarde 2003 which has been cutting out when driving, causing loss of power steering etc. it's been into garage today and had crank sensor changed. No faults showing. They ran it for. 3 hours with no issues, as soon as she got into it it cut out on her again. Any ideas as it's costing her a fortune

This could be a wiring issue as things tend to expand when hot and its possible a poor or partial electrical connection is being pushed apart on one of the major sensors so check the connection plug and wiring to the following;
Airflow meter
Crank position sensor
Cam position sensor
O2 sensor
Throttle position sensor

Also worth checking the connections to the fuel pump for the same reason - unplug each in turn and give them a good squirt of switch / contact cleaner - Not WD40

and also unplug and inspect the main power relays and fuses for signs of overheating or corroded terminals - so the ones for the ECU and the fuel pump

And also unplug the wiring loom connections in the engine bay one at time and inspect for corroded or recessed pins.
also check for any oil on the end of the sensor wiring looms as you can get the situation where oil enters the wiring from a component that is leaking, into the wiring harness andyou then have to replace the component and clean or replace the wiring
.Usually this can short out a data circuit or control circuit and can cause issues like this here
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Customer: replied 3 years ago.
I take it none of the above would show on a diagnostics check. There was nothing showing when they checked today
Hello Dawn

wiring faults don't always show up on diagnostics as the ECU looks for a set of values from each sensor which can be fooled by an earthing fault