Mercedes-Benz W140 mass air flow sensor fault
S 500SEL 500
What are the symptoms of a faulty mass air flow sensor on the W140?
The engine runs unevenly or the revs fluctuate. The car can also run rich or go into emergency mode, in which the engine control unit uses fixed values. A car that runs poorly when warm and takes long to start can have the same fault.
Why does the W140 engine control unit go into emergency mode because of the mass air flow sensor?
The control unit monitors the sensor's circuit. If the circuit does not respond with the expected value, it goes into emergency mode. That is why even a fault in the sensor's wires or internal solder joints is enough to cause it.
How is a W140 mass air flow sensor fault repaired?
Check the sensors and their wires. Repairing the wiring harness alone is not always enough, and the sensors may have to be replaced. The internal solder joints of an old sensor can also be re-soldered. Reading the fault code helps point to the sensor.
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