Coolant Temp Sensor - 91 300-SEL
 

1991 300-SEL - M103 - 6 cyl

Check Engine Light comes on after idling up from a cold start in about 7 mins. Pulled the following codes:


13 - IAT - intake air temp sensor
22 - O2 sensor
31 - CTS - coolant temp sensor

Research reveals that not all of these may actually be defective. One or maybe two defective components could be causing all 3 codes. I'll have to dig.

I know where the IAT and O2 sensor are. There are supposedly 2 CTS' on this engine. One is for the temp gauge in the dash cluster; the other communicates with engine/fuel mgt.

Would anyone know if the part in the 2nd URL below is the sensor that communicates with engine/fuel mgt?

In my case - it's at the rear of the cyl head next to an engine hoist bracket. The elect. connector is 4-prong. Beru part number is 008-542-32-17-M47 - found in 1st URL on the right side of screen along side of part.

http://www.pelicanparts.com/catalog/SuperCat/3371/MBZ_3371_WATMIS_pg2.htm#item1

http://www.pelicanparts.com/cgi-bin/smart/imgdsply.cgi?pn=0085423217-M47







Thanks for your time.

Yes, the second link with the four prongs is for the CIS ECU.

The single pole unit is for the dash gauge.



Test the sensor before you replace stuff.

Thanks.

I queued up with another reputable online MB parts seller. They said the same.

In a post going back to 2002 - former founder(one of them) of mercedesshop.com - benzmac - indicated the M103 motor had 3 coolant temp sensors.

- coolant temp sensor - CIS/EZL - fuel mgt
- coolant temp sensor - Dash temp gauge
- coolant temp sensor - Aux. fans

My 1991 MB 300-SEL M103 has a 4 prong coolant temp sensor at the very back of the cyl. head. Not all M103 motors have this 4 prong sensor. In my case - this 4 prong sensor signals both the CIS/EZL and the Aux. fans - therefore eliminating one of the sensors.

A single pole sensor signals dash temp gauge as mentioned by previous poster.

008 542 3217 - CIS/EZL-fuel mgt - Aux. fans - 2 sensors in one

005 542 2617 - Dash temp gauge
|__replaced by 005 542 1017 - either one is valid if available

Will ohm test 008 542 3217 before replacing. I have a gut feeling that once the O2 sensor is replaced - the CTS/IAT codes will clear up. The O2 sensor is original - 24 yrs. old.