P0856 error on R350L 4matic

R350L · Oct 15, 2015

Hi all,

The other day my check engine light came on. I hooked up a scanner and was able to pull the following code:

P0856
Y110 (three-disk thermostat valve): Short circuit to ground or to positive (P0128)

I noticed that the coolant temperature reaches 65-70 degrees Celsius at the max. instead of its normal operating temp of 80 degrees Celsius.

It could be a dirty connector as there is an electrical connector on the thermostat's housing and the scanner reports a short circuit.

Anyone else encountered this code on a R350L 4matic (2006) or similar model? How did you fix it?

Best regards,

William

marc hanna · Oct 16, 2015

I haven't had the problem, but you could dose it with some electrical contact cleaner and then apply some dielectric grease to it the contacts and see if that solves the problem. I would recommend disconnecting the battery.

Otherwise, you likely need a new thermostat.

octoberone · Oct 26, 2015

P0856 is "thermostat stuck open" - the coolant will keep cooling down the engine no matter whether it is cool enough.

R350L · Oct 26, 2015

Thanks guys, I ordered a new Wahler thermostat in Germany (€62) and hopefully this will fix the problem.

P0856 error on R350L 4matic

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