Mercedes radiator fan turning on when ignition switched off!
Discussion
Hi,
Car in question is a 2013 Mercedes C250 CDI
Very simply, when I switch the ignition off, within a minute the engine cooling fan turns on to full and sounds like a jet turbine until the battery dies. The fan turns off when the ignition is turned on and the car drives and runs fine otherwise. Two garages have looked at it including a Mercedes specialist with STAR diagnostics and neither know whats going. No codes, nothing. Battery has been load tested and is fine. The Merc specialist have recommended changing the fan unit so as to change the fan control module etc but they admit they are stabbing in the dark.
Any ideas? Getting desperate.
All comments welcome. Thanks.
Car in question is a 2013 Mercedes C250 CDI
Very simply, when I switch the ignition off, within a minute the engine cooling fan turns on to full and sounds like a jet turbine until the battery dies. The fan turns off when the ignition is turned on and the car drives and runs fine otherwise. Two garages have looked at it including a Mercedes specialist with STAR diagnostics and neither know whats going. No codes, nothing. Battery has been load tested and is fine. The Merc specialist have recommended changing the fan unit so as to change the fan control module etc but they admit they are stabbing in the dark.
Any ideas? Getting desperate.
All comments welcome. Thanks.
Has the coolant temp sensor been checked?
On my car it is sited in the rad top tank. Sometimes on switching the engine off it stays on (if already running due to coolant being >95C) or kicks in after a minute due to heat sink as hot coolant migrates to the rad top. It does switch off though when the coolant temp drops back. It is actually working correctly by detecting localised overheated coolant and is wired to switch when ignition is off to be able to do this.
If yours stays on to drain the battery then is it faulty sensor? Possibly the cheaper repair rather than modules!
On my car it is sited in the rad top tank. Sometimes on switching the engine off it stays on (if already running due to coolant being >95C) or kicks in after a minute due to heat sink as hot coolant migrates to the rad top. It does switch off though when the coolant temp drops back. It is actually working correctly by detecting localised overheated coolant and is wired to switch when ignition is off to be able to do this.
If yours stays on to drain the battery then is it faulty sensor? Possibly the cheaper repair rather than modules!
Can you or the garage lay your hands on a "known good" fan? It wouldn't even have to be mounted properly to your car, so long as you can get the wires plugged in (or bodge an extender) and then you'll see if it's the fan or not.
If the fan's electrics are cleverly mounted on the fan itself, ie one of the hottest points in the car, just behind the rad, I know I wouldn't be surprised by a failure... at least it's failed "on", which is better than only finding it has failed "off" when the engine goes "pop" in a traffic jam!
In the meantime, fit an on-off switch in the wiring
If the fan's electrics are cleverly mounted on the fan itself, ie one of the hottest points in the car, just behind the rad, I know I wouldn't be surprised by a failure... at least it's failed "on", which is better than only finding it has failed "off" when the engine goes "pop" in a traffic jam!
In the meantime, fit an on-off switch in the wiring
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