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Hipo64
Hipo64, Mercedes Technician
Category: Mercedes
Satisfied Customers: 3485
Experience:  Work and diagnose electronics on daily basis.
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2006 clk350: high speed..overheating..alternator diagnostic test done

Resolved Question:

Hello guys I am working on a 2006 clk 350 (272 engine) and the engine fan keeps spinning at high speed . The vehicle is not overheating . The battery light came up on dash and the alternator diagnostic test done with Star diagnosis machine . The alternator failed the load test and the regulator was replaced upon which charging returned to normal .What could be causing the fan to spin at high speed constantly with A/C on or off .
Submitted: 5 years ago.
Category: Mercedes
Expert:  Hipo64 replied 5 years ago.

Hipo64 :

Hi and Welcome to Just Answer!

Hipo64 :

it sounds like engine computer has lost power or communication.

Hipo64 :

cooling fan will come on as safety future

Hipo64 :

if you have another car there disconnect computer with ignition in on position and fan should come on at high speed.

Customer:

how do i get the fan working normally again .

Hipo64 :

you need to scan the vehicle for fault codes. also check engine computer power supply circuits.

Customer:

i have fault code 0750 self adaptaion of mixture formation for enleanment left cylinder bank.0521 diagnosis tumble flap "intake manifold " short circuit to ground tumble flap sticks in actuated position . 0746(p0172) self adapation of mixture formation for enleanment at idle for right bank is below permissible limit .2092 mixture in right bank is too rich when idling . 2096 the mixture in the left cylinder bank is too rich when idling . 1337 alternator serial interface. All these codes were presnt when I initially scanned the vehicle but besides the alternator code didnt see why it would keep the fan running at high speed hence the reason for not mentioning it earlier . the car starts and runs (do you still want me to check computer power supply )

Hipo64 :

yes check computer power supply and 5V reference voltages. if codes are present with engine not running, there is problem with electricl system

Customer:

i will do as you say tomorrow , with the power supply and reference voltages one final question . if the power supply and reference voltage is ok but the fan still runs at high speed are there any other suggestions .

Hipo64 :

if it works high speed without engine running and all circuits and cignals OK. -ENGINE COMPUTER FAULT

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