From another forum...

[Rawze]

(10-13-2023 )JMBT Wrote:  Volvos with red motors actually use a temp sensor, marked as temp 1, in the DOC/DPF can… or at least they did on CM2250’s

I think you guys are confused there on the engine side of things ...

Most all ISX's have this sensor in the DOC/DPF ..... but it is not actually used for engine EGT feedback. it is used for DOC/DPF inlet temps and not for engine output exhaust temps at all.

The setting 'C_EMT_Virtual_Sensor_En' (exhaust manifold temp input selection) is always set to one, and there is not even an input for it in the analog inputs sensor manager for it. I even looked up your exact CM2250 engine ser# there JMBT, and its set exactly like every other truck with a CM2250 ISX.

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On the Volvo's with the X15 enignes, it is set the same exact way.

The newer X15 programming in general does have some added minimal logic for an exhaust temp sensor in the analog inputs manager, but it is unused, and it is not even complete enough to assign a J1939 address to it, nor a pin in the face of the ecm. Nor is it tied into any other sensor.

And also, as such, if any system was actually using that input DOC temp1 sensor... a proper de-mandate would have made the gauge go to zero, because a decent de-mandate disables all of the the DOC/DPF input temp and other sensors under there.

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Of course, none of this has anything to do with any dash display of the vehicle side of things. The engine simply calculates EGT's, and has never been very accurate at it. This has been seen time and again. For accurate EGT feedback, a person needs a gauge with an actual feedback sensor for it installed.

So ... If there is a factory EGT gauge, Volvo, pete, kw, or otherwise, then it is either using its own feedback, separate from the engine, or it is only reading the estimated EGT which is not very reliable.