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Mercedes C180 W203 coolant fan on constant

Coolant fan is on constant. The signal wire from the engine ECU to fan was cut but the fan still operated on full power, replaced fan but problem still exists, any ideas.

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The fan is on because the wire is cut. If the ecu does not detect a signal from the fan switch it will default as on. Replace the wire and fan temperature switch and all will be ok

Posted on Apr 15, 2014


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SOURCE: coolant fan on 2000 S430 Does not work ,but fan motor is good,

they don't run all the time only when the temp sensor tells them. is the car overheating?

Posted on Aug 17, 2009

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My c180 2005 model had wouble engine noise when i started the engine to have it parked in the garage. Engine light was on. I drove it within 5metres into the garage. I towed it o mercedes and they d

Check the spark plugs, the spark plug wires and the coil packs. If they are good then the misfire could be caused by the Mercedes ecu computer. If you are not sure go to for more information about ecu misfire problems.

Dec 31, 2014 | 2002 Mercedes-Benz C180


Bad fuel economy and lumpy idling - possibly causes

<p><b><u><span>Excessive fuel consumption and 'lumpy' idling engine</span></u></b><br /> <p><b><span>Possible faults:-</span></b><br /> <p><b><u><br /></u></b><br /> <p><b><u><span>Coolant sensor </span></u></b><span><span> </span>- engine is signaled as being 'cold' all the time, not just at start up, causing ECU to set longer injection cycle </span><br /> <p><span><span>&oslash;<span> </span></span></span><span>Low coolant level can prevent sensor being able to detect coolant temperature</span><br /> <p><span><span>&oslash;<span> </span></span></span><span>Faulty 'open' thermostat allows coolant to circulate without regulation and perhaps prevents the engine from achieving normal running temperatures.</span><br /> <p><span> </span><br /> <p><b><u><span>FPR</span></u></b><span> - broken diaphragm allows fuel to enter the vacuum line and then into the inlet manifold. Additional source of fuel makes the fuel air mix richer causing a faster and lumpy idle.</span><br /> <p><span> </span><br /> <p><b><u><span>Vacuum leak </span></u></b><span>- 'high oxygen' signal from O2 sensor causes ECU to set longer injection cycle.</span><br /> <p><span> </span><br /> <p><b><u><span>O2 sensor</span></u></b><span> - 'high oxygen' sensor error causes ECU to set longer fuel injection cycle</span><br /> <p><span> </span><br /> <p><b><u><span>MAF</span></u></b><span> - 'over reads' in error the amount of air entering causing ECU to set longer fuel injection cycle </span><br /> <p><span> </span><br /> <p><b><u><span>IAT</span></u></b><span> - 'under reads' in error the temperature of incoming air causing ECU to set longer fuel injection cycle</span><br /> <p><span> </span><br />

on Jul 22, 2011 | Mercedes-Benz E-Class Cars & Trucks


ECT - Engine Coolant Temperature sensor

<p><b><span>2.2) <span> </span><u>ECT - Engine Coolant Temperature </u>(sensor)<u></u></span></b><br /> <p><b><u><span><span> </span></span></u></b><br /> <p><b><span>What is it?</span></b><span> This is small electrical device for measuring the coolant temperature in the engine</span><br /> <p><span> </span><br /> <p><b><span>Where is it located?</span></b><span> It is usually located on the engine near to the thermostat housing.<span> </span>The ECT is sited on the 'hot' side of the thermostat so that it senses the coolant/engine temperature before the thermostat opens and allows coolant to flow through the radiator.</span><br /> <p><span> </span><br /> <p><b><span>How does it work?</span></b><span> Modern temperature sensors consist of a thermistor in a sealed unit.<span> </span>As the temperature rises the electrical resistance varies proportionately; some thermistors increase their resistance with temperature (PTC - positive temperature correlation) whilst others decrease their resistance (NTC - negative temperature correlation).<span> </span>When the engine is cold at start up the coolant sensor sends an appropriate signal to the ECU.<span> </span>The ECU responds by increasing the length of the injection cycles to enrich the combustion mix.<span> </span>This is an electronic equivalent of pulling the 'choke' out on a carburetor.<span> </span>As the engine warms up the signals from the coolant sensor cause the ECU to shorten the injection cycles making the fuel mix progressively leaner.<span> </span>The process of coolant sensor and ECU interaction explains why engines have a slightly faster idle when starting cold than when running hot.</span><br /> <p><span> </span><br /> <p><b><u><span>Symptoms of faulty coolant sensor</span></u></b><br /> <p><b><span>Associated OBD2 error codes DTCs: <span> </span>P0115 - P119; P0125, P0126, P0128</span></b><br /> <p><b><u><span><span> </span></span></u></b><br /> <ul> <li><b><span>Poor starting</span></b><span> - If the coolant sensor reports in error that the engine is warm the ECU will not enrich the fuel mix at ignition.<span> </span>The engine will falter at idle if it is not given additional help by the driver by pressing on the accelerator pedal to maintain speed.<span> </span>Once the engine has warmed up the engine will behave correctly.</span></li> <li><b><span>Fast/erratic idle, Poor fuel economy - </span></b><span>conversely if<b> </b>the coolant sensor reports in error that the engine is permanently 'cold' the ECU will keep the fuel mix rich.<span> </span>This is OK at start up but will become more noticeable when the engine is hot; idle will be fast and lumpy.<span> </span>Fuel consumption will be high due the permanently rich fuel mix set by the ECU.<b></b></span></li> <li><b><span>Excessive emissions - </span></b><span>the enriched fuel mix delivered in response to ECT signal error causes the exhaust to be heavy in un-burnt hydrocarbons.<span> </span>This often results in 'emission test' failure.<b></b></span></li> </ul> <p><b><span> </span></b><br /> <p><b><span>How to check? </span></b><span><span> </span>Most often the <b>coolant sensor</b> is quite separate to the <b>temperature sender</b>, so a correct read-out on the dash board does not necessarily indicate correct sensor function. Using<b> </b>a voltmeter the resistance across the electrical terminals on the sensor can be measured.<span> </span>By removing the device from the car and putting the end of the sensor in a pan of hot water it should be possible to see an immediate change in resistance, it does not matter so much that the resistance goes up or down but that there is a discernable change with change in temperature.<span> </span>Generally high resistance equates to cold temperatures and vice versa. If there is no resistance change commensurate with temperature change then the sensor is at fault.<span> </span>If there is simply no resistance measurable (open circuit) then the sensor is at fault. If the sensor is working correctly check the connector, the wiring and the wiring insulation for faults and possible shorting.</span><br /> <p><b><span> </span></b><br /> <p><b><span>How to fix?<span> </span></span></b><span>Replace if found faulty</span><br /> <p><span><br /></span><br /> <p><span><b>NEXT 3.1) CKP - Crankshaft position sensor</b></span><br />

on Jul 22, 2011 | Mercedes-Benz E-Class Cars & Trucks

1 Answer

What do i need to fix to make the cooling fan work on my 1994 saturn SC2? Tried brand new relays(multiple) and nothing worked.

I would make sure the coolant temperature sensor is operating correctly. The 2 wires that are jumped into the distribution center are the load side of the relay, the other 2 blades in the relay base are the 12v signal and the ground. You can take a multimeter and make sure you have continuity to ground through one of the blades, the other will be the signal from the ECU witch gets its signal from the coolant temperature sensor.

Aug 02, 2014 | Cars & Trucks

1 Answer

Mercedes c180 steering


Sep 19, 2013 | Mercedes-Benz Cars & Trucks

1 Answer

C180 ac

You may need a mechanic for this.
In most cases the radiator fan is not pulling enough air thru the condenser when you are not moving. Either the fan is not running or there is a blockage.

Jun 09, 2013 | Mercedes-Benz Cars & Trucks

2 Answers

Car is overheating ...already replaced waterpump, flushed radiator, changed thermastat and replaced new water cap. there is no leak, and it over heats sometimes not everytime?

Make sure the small hose going from the reservoir to the radiator and the orifice at the reservoir are not clogged. If OK, check electric cooling fan system, specifically the Coolant Temp. sensor, Fan Relays and Constant Control Relay Module (CCRM).
Electric cooling fan system consists of a fan and electric motor attached to the fan shroud.
  • Engine temperature is monitored by the Engine Coolant Temperature (ECT) sensor.
  • Fan is controlled by Constant Control Relay Module (CCRM) with inputs from Powertrain Control Module (PCM).
The electric cooling fan is wired to operate only when ignition switch is in ON position and engine temperature exceeds specified temperature, or when A/C is on and vehicle speed is less than 45 MPH. During hard acceleration, the Wide Open Throttle A/C Cut-Off (WAC) relay controls the A/C clutch and cooling fan. A signal is sent to PCM and then to the CCRM, where the module de-energizes the A/C clutch and cooling fan, decreasing engine load during acceleration.
Good Luck!! A HELPFUL - 4 THUMBS - rating for this solution would be greatly appreciated. Thank you for using FixYa!!

Feb 16, 2011 | 1996 Lincoln Continental

1 Answer

Coolant fans are not running. unplugged coolant

Check out coolant temp sensor ,its wiring and condition of coolant all together they control that circuit.
Then make sure ECU is getting Temp sensor signal and is sending it to the relay accordingly. ( which in your case is probably not the problem because the fans went on when you removed and accidently grounded coolant sensor wiring) Only one thing left Good luck

Mar 24, 2010 | 2001 Chevrolet Venture

1 Answer

1994 c280

The 2 AC fsnd turns on when the Engine temperarure hot. It receives the signal from ECU throught the Engin temperature sensor ( Coolant). Your case happens since the Engine Temp sensor went bad. At beginning the temp sensor can not produce any resistance just like open then ECU thinking engine hot turns on the Fan. When your engine ia about 85, it is a normal temp then the sensor could produce some resistance matching the look up tabel for the ECU, then the ECU turn off the Fan. Some pepople has it run all the way since the wire contact to the sensor was off. Replace the Engin Temp sensor to take care of the problem.
You have 2 temp sensors on top engine, one for your temp read out, one for the fan purpose. If you don't know which one, wait for your temp at 85 and the fan is stopping, then unplug one, imediately the fan goes on, that the one. Good luck.

Jul 05, 2009 | 1994 Mercedes-Benz C-Class

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