Intermittent temperature guage & coolant fans running.

Mar 13, 2023 | 02:53 PM

Merc E350

Thread Starter

Newbie

Joined: Mar 2023

Posts: 1

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E350 W212

Intermittent temperature guage & coolant fans running.

Hi all. I don't know if someone can help. I have a 2013 E350 W212 and am occasionally have some strange issues where the temperature guage won't rise at all and the cooling fans come on. If I switch off the engine and switch back on again the temp guage goes up and the fans go off. It's not every time I drive it, just every now and again.

Thanks to everyone in advance for any help.

Mar 13, 2023 | 04:22 PM

CaliBenzDriver

Out Of Control!!

Joined: Apr 2019

Posts: 11,924

Likes: 6,776

From: Silicon Valley

W212 MY'14 M276-3.5NA @75kMi

tricky failure...

Quote:

Originally Posted by Merc E350

Hi all. I don't know if someone can help.

I have a 2013 E350 W212 and am occasionally have some strange issues where the temperature guage won't rise at all and the cooling fans come on.

If I switch off the engine and switch back on again the temp guage goes up and the fans go off.
It's not every time I drive it, just every now and again.

Thanks to everyone in advance for any help.

> RECAP:
Intermittent wrong temperature sensing once a while with supersonic fan on.

You have the conditions pretty well defined

so we can have a better focus!

> 1...2...3 Bingo:
All preliminary attention would be focused on sanity checking the temperature sensor (not the A/C pressure sensor).

However you've noted restarting the car clears this issue! We know the engine temp is doctored and posted on the CAN bus for the iCluster to display.

Essentially the ECU is distrusting the sensor for some reason then racing the fan as a form of cooling protection plus driver warning.

The $2,000 question then becomes: what failure causes the ECU to engage in safe-mode cooling ?

> PRELIMINARY CHECKS:
We want to rule out bad sensor circuit, unit or wiring.

1- Have a look at the connector to see if coolant is leaking through the pins into the connector.

2- Read the temperature data with your scanner when this happens.

> ADVANCED CHECKS:
We want to figure what pushes ECU over the edge.

1- Scan for ALL faults for health assessment.

2- Suspect something fancy or classic poor GND.

That means you may have a "no parts", labor only repair.
🤞

Last edited by CaliBenzDriver; Mar 13, 2023 at 04:44 PM. Reason: safe-mode cooling