Exhaust gas temp sensor

[steve-V8s]

Up stream from the DPF on my diesel Merc there is a gas temperature sensor. I am making the assumption that the ecu uses this to determine if the temperature is nice and hot before throwing in a bit more fuel to clean the filter. I have an intermittent management light and a code reader points towards the temp sensor reading being out of range ( -172c) .

Is this going to be something like a thermocouple generating a temperature related voltage or is it going to be a temperature related resistance ? If I knew what the ecu was expecting I could simulate the sensor or at least measure the output.

[anonymous-user]

Most EGT sensors have a built in amplifier to convert the raw signal from the probe into a suitable votlage level for the ecu to read. Sensors tend to be thermocouples (for robustness reasons) and the output can be 0-5v analogue, but more often it's Pulse Width of Frequency modulated TTL. They also tend to have a limited range, often 500degC to 1000degC, as anything below about 500degC is irrelevant.

You have to find out exactly which sensor is used on your engine to be more sure what type it is.

(Pieburg, Denso, and Bosch all do them)

[GavinPearson]

For information the EGT sensor is there to control the temperature of the turbocharger exhaust gas turbine so that they don't need to use high nickel content alloys.

[steve-V8s]

In this case I think there are two sensors, one in front of the turbo and one in front of the DPF, it is the DPF one I am interested in.

The part has a simple two pin connector so I am assuming it is a thermistor. If it had an inbuilt amplifier or pwm driver I would expect more pins.

I would be interested to know the normal resistance range. The example I have changes from 200k when cold to 300k hot. I would expect a bigger change and a significantly lower reading.