EGT sensor

[Neils65]

Hi All,
I have just had my EGT sensor replaced as the eml came on and I used Icarsoft mb2 to diagnose. Took it to a local service garage who diagnosed the same. Had it replaced but yesterday the eml lit up again (yellow) with the same EGT issue. My car is a 2012 c220 blue efficiency diesel. The traction control and run flat indicators flash up sporadically and put it in limp mode, restricting it to 60mph but stop the engine and immediately start again and it is all back to normal. Not sure where I should go with this, could it be the front SAM? Any help would be appreciated

 

[Supernoodle]

You haven't stated what EGT fault you have, but if it's a circuit fault it doesn't necessarily mean the sensor is at fault, you should check the wiring first.

 

[Neils65]

Hi there, originally it was P0546 but there is no actual code now it just says EGT cylinder 1 short or open circuit or words to that effect. I have driven into work (approx 50 miles) this morning and no eml but I’m sure that it will reappear on my way home. Any suggestions regarding tracing a wiring fault?

 

[Supernoodle]

The module reports a code, which the tool translates to description, so there will be code but the important bit is the Exhaust Gas Temperature sensor open or short circuit to power description.
The EGT is a simple two wire device. It is nothing more than a resistor which forms one half of potential divider (if you remember those from school). One wire connects to a ground, the other connects to a sense pin. This pin is internally within the ECU is also pulled up to 5volts via a resistor. The resistance of the EGT varies with temperature, this variation changes the voltage that appears at the sense pin.When EGT resistance is high, sense pin is at 5v, as resistance lowers voltage at sense pin tends to 0v.
So if the EGT is open circuit, ECU sees 5v at the sense pin.That could be sensor fault or wiring between sensor and module, it can't tell difference, you need to check.

If none of that made sense, first just check across the ECU side of the temp sensor connector with it disconnected, you should see 5v. If not check individually for power/ground using a known ground and known supply. Then you can check for continuity between connector and module.

EGTs are the simplest of sensors and work the same on just about every car, a garage should know how to check these issues.

 

[Neils65]

Very much appreciated, thank you.