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Old 01-08-2009, 02:11 PM
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Join Date: Nov 2000
Location: Knoxville, TN USA
Posts: 56
W140 Duovalve or Temp Sensor

The heat stopped working on the passenger side of my '98 S420. I ran the diagnostics and found the temperature (4) on the right side heater core to be about the same as the ambient while the left side (3) displayed heated coolant. Unfortunately it would appear that the duovalve has failed, however, in running the trouble codes for the system though no code was thrown for a failed duovalve (B1418) also I checked continuity for the coils as suggested by the "V12 uber alles" rebuild instructions and found it to be ok.
Before parting with $500 to replace, I would love to check the temperature sensor operation first. Where would I find said sensors. The overhead cabin pump sensor is fine but I just can't fine the heater core sensors.

Any help would be appreciated.


Steve Short
'91 300SE sold
'92 190E 2.3 sold
'99 S420
'06 Mini Cooper S
'08 Triumph Rocket III
'02 CLK430
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Old 01-18-2009, 03:17 PM
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Join Date: Jan 2009
Posts: 2
Check out this website. It has good schematics of your car.

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