Outside temp reading too high

AmoS500

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SLK250 R172
Hi, the digital temp reading is showing readings above 35 all the time.
I have been told that the sensor is on the front bumper but where?

Pls help

thanks
Vito 2004 Traveliner 109cdi
 

Xtractorfan

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Normally slotted in beside one of the spotlamps.. yours may have come adrift..
 
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AmoS500

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SLK250 R172
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Thanks, how can I get to it pls and what does it look like

rgds
 

Xtractorfan

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If you carefully scan across the bumper, especially around the spotlamp covers you will see a little round hole, check round the back of that area and you will see some wires plugged into the bumper, on the end will be a little probe, tht is your temp sensor
 

Hertfordshire Merx

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Unfortunately they do fail reasonably often and can cause starting problems and fuel consumption issues so get it sorted quick!!!!:neutral:
 
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AmoS500

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Unfortunately they do fail reasonably often and can cause starting problems and fuel consumption issues so get it sorted quick!!!!:neutral:

WOW never thought a temp sensor could affect so much!, thanks will find it asap!
 

Hertfordshire Merx

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WOW never thought a temp sensor could affect so much!, thanks will find it asap!

Yes, the ambient temperature data is put on the engine and body CAN network to be distributed to the control units needing the information such as the A/C control unit, engine control unit, instrument cluster etc etc.

If you think about it logically, if the outside temp is registered as too low, the engine control unit will adjust the injection opening time so more fuel enters the engine for cold start etc. Hence you'll use more fuel.
 
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AmoS500

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Hi, Just been off the phone to Mercedes and a local Merc specialist, both said that the ambient temp has no impact to the ECU etc..., it is purely for the driver.
 

johnmearl

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does any one know the part number for a outside temperature sensor for a E240 1998
 

SQ_W211

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Hi, Just been off the phone to Mercedes and a local Merc specialist, both said that the ambient temp has no impact to the ECU etc..., it is purely for the driver.

They may be telling porkies but it will have impact on the car running maybe not soo much on the fuel consumption.

The fact that you are getting a very high read, it may have sloted out of the bumper insert and gone near the radiator which may give higher reading....
 

rayhennig

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Is this true?

On a 124, the sensor was for the driver only and is behind the number plate. When the car is in the sun, I often see 40+ C on the readout but the true amblient temp is, perhaps, less than 30.

To answer the original post, if it's reading consistently high, I would assume the sensor to be faulty. Mine was and it was easily fixed with a new sensor.

I doubt whether this sensor would be used for engine management, even in a newer vehicle. There are sensors on the engine and these measure ACTUAL ENGINE TEMP, so why confuse the issue?

Having said all that, I don't know about later vehicles so comment from the wise would be appreciated.

RayH
 

television

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The outside temp wire goes straight to the instrument cluster and no where else,,it was an extra on some cars.

When they fail they show 38c there abouts and have no effect on the engine.
 

INKJET

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TV is spot on

I had the same problem on my 2000 model CLK , the bumper had been off for some paint repair work and the sensor had come out of it holder, it was in an area behind the bumper and close enough to the radiator to allow air from the rad to pass the sensor to give a higher reading than ambient.

It is also easy to push it out of the sensor when cleaning the car with a sponge if you heavy handed.

The location (on both my 2000CLK & 2007 E class estate) is to the right of the number plate when viewed from the front and is located in the dumy black mesh grill's near the fog lamps, it is a small cone shaped sensor and protudes only a few millimetres, so it is easy to miss, if you have just a hole there, then it's probably pushed back through behind the bumper, you can access this by removing the small under tray on the near side, three screws i think.

If its reading ambient when the car has been left overnight, but increase the faster you go then that's the likley cause
 

Hertfordshire Merx

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OK to clear things up I have checked WIS and looked at the function of the ambient temperature sensor for a number of different vehicles and they all work the same from various months in 1996 onwards.

I have the information for a vito (document number GF54.30-S-3019SH) so here goes:

To display the temperature, the outside temp indicator requires, the outside temperature, a speed signal and the engine running time. and as of 1996 it also requires the engine coolant temperature.

The speed signal, engine running time and engine temperature are determined internally by the instrument cluster.

The outside temperature is read in by the SAM control unit (N10) and passed as a value on to the Interior Network CAN 'B'. The instrument cluster therefore picks up the temperature from the CAN network and processes the this data and controls the display accordingly.

Since the outside temp display depends on the speed, engine running time and coolant temp, high temperatures (influenced by the heat generated by the engine and radiator for example) are not displayed when the vehicle is stationary or moving slowly.

The sensor consists of a negative temperature coefficient (NTC) resistor. The NTC integrated in the outside temp sensor (B14) changes its electrical resistence according to the outside temperature. The electrical resistance decreases as the outside temperature increases. Temperature range is -40c to +60c/140f.

Hope this helps you out.
 

television

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Could the Vito be different to the cars,,it was an extra on many
 

Hertfordshire Merx

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Checked WIS and raised document GF54.30-P-4104A, which is applicable to 129, 140 >1.6.96, 170, 163, 202 with accessory code 240a (outside temp display), 202 as of 1.8.96, 168, 208 up to 31.7.99 and 210 as of 1.6.96 up to 30.6.99

Was only an option on 202 by the looks of it.

same relevance applies as with Vito.
 

television

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Checked WIS and raised document GF54.30-P-4104A, which is applicable to 129, 140 >1.6.96, 170, 163, 202 with accessory code 240a (outside temp display), 202 as of 1.8.96, 168, 208 up to 31.7.99 and 210 as of 1.6.96 up to 30.6.99

Was only an option on 202 by the looks of it.

same relevance applies as with Vito.

Thank very much, I will take a read of it all :D:D:D
 

Alex Crow

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but the outside temp sensor has no impact on engine function does it? the coolant and intake air temp sensors handle it all.
 

Hertfordshire Merx

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The temperature sensor is wired into the front SAM and the data it produces is put onto the CAN 'B' network (body CAN) it is then sent into the instrument cluster (which is a control unit in its own right) which puts it out onto CAN 'C' (chassis CAN).

I havent had time yet to look into where it would be relevant to what control units from that point onwards, I'll take a look later when I have finished todays work.
 

pauline66

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hi my temp gauge is showing 120 and car gower i checked water and oil and they were fine i even left car for a day to see if it would be ok and when i started my car on a cold engine it went straightto 120 again and the fan kicks in but today i started it and it was bouncing up and down between 0 and 60 what cbe everyone thinks it may be a blockage or thermostat sticking.thankyou
 

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