Coolant Temp Sensor - 91 300-SEL

[Mike Richards]

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.

[Hit Man X]

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.

[Mike Richards]

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.