Testing the Thermostat "Coolant Visit Workshop" fault

[steveatesh]

Need some help with my CLK 270D 2005 reg. Basically every time I start the car a few seconds after the engine starts I get the "Coolant Visit Workshop" fault up. From various forums I understand this can be anything from the radiator Suction Fan and module (expensive), the fuse, wiring, ECU, or the thermostat/coolant temperature sensor.

The fan starts at Fast mode and stays in that mode until a few seconds after switching the car off. I understand this is a safety mode and it is behaving correctly with this fault code. The engine temperature never really gets hot and hovers around the 60 degrees or so.

The fault developed while the car was SORNED, along with an Air Con fault which turned out to be a loss of refrigerant through a seal (repaired and working no problem now).

The fault showing is P1636-008 "Electric Suction Fan Open Circuit". This was at a Merc independent who was replacing a suspension part for MOT -I didn't ask him to go any further because he started blaming the Fan Module straightaway and quoting £500 plus at least.

I have checked Fuse 51 and a visual check of the accessible wiring looks fine. Before resorting to a dealer or Indy I would like to check the Thermostat/coolant temperature sensor as this is relatively easy repair. With the engine temperature sticking at 60 degrees or so I am conscious it may well be the Thermostat sticking open, but have no idea whether this would produce the fault as above (or it may stick at this temperature because the fan is at full speed?)

I am wondering if there is a way to test the thermostat in situ that I can do myself, or does anybody have any other suggestions? I have posted on MBClub but not received a single reply

thanks in advance.

[mbtech01]

From what you've described it does sound like the suction fan is faulty. Sometimes the main multiplug that's sits at the bottom can corrode & rot the terminals away. you'll need to remove the front undertray & you'll see the big multiplug sitting on the L/H (passenger) side at the bottom of the suction fan. It usually has to very thick wires/terminals & two small wires/terminals located in the terminal block. Just release it & have a look to see what state its in.
Regards the thermostat you may be right in that because the fans running all the time the cars never allowed to warm up fully, but on the other hand if the cars been laid up for a while & not been used you may have a lazy thermostat that's not closing fully & not allowing the engine to reach operating temp. Its not uncommon on older cars & I've just had the same problem on the wife's Bmw & ended up replacing the thermostat.
Hope this helps a bit & if I think of anything else I'll update you.

[steveatesh]

Thanks very much for your response. I'll check out the multi plug, but do you think the problem could be a faulty coolant temperature sensor as the root cause?

[mbtech01]

From my previous experience it sounds like the suction fan is your root cause but don't take my word for it until you rule out various things like the coolant temp sensor etc. There may even be a short in the wiring & if memory serves me right check the wiring that runs under the battery carrier as this is where the wiring from the engine ecu to the suction fan runs & may have rubbed through & be shorting out. As said I can't guarantee it but it's worth a check. As you previously mentioned the vehicle has been stood for some time & it's also a possibility that some mice or something similar may have decided to nest or feast in the scuttle area as they particularly like to feast on wiring looms etc.