2006 379 Pete w/cm870 ISX.

[Rawze]

(10-18-2023 )Peashooter67 Wrote:  I found this mystery ambient air temp sensor and found it by accident.
In insite the ambient air temp sensor is actually your egr temp sensor or at least I think it is.

It was reading erratically for a while causing derates and high egt and then one day shortly after my query here it just quit and put out three dashes. This week end I got really tired of running incercles with no resolution from anywhere and just start unplugging every wire plug I could find.

Wow

When I unplugged the egt temp sensor all the sudden the ambient air temp sensor started showing a reading of 72* constant with no change. Plug it back in - - -, unplug it 72* and my full throttle derate went away.

I am not so sure that the amb sensor itself is actually the egr temp sensor. You likely still have not fount it.. or it may be calculated (some vehicles, it is only calculated) via looking at several other sensors. The ambient temp sensor does compare itself to other sensors at ecm power up, so it could simply be coincidence that the faulty EGR temp sensor was effecting the amb sensor readings indirectly.

Also, that particular temperature of 72 (or sometimes 73) F is used as a default value, assigned to the amb temp sensor, when it bypasses and cannot be evaluated properly.

I.E.> Your description of what happened to the amb sensor is very coincidental to what happens when it falls back to its default value, and not reading any actual temps, for one reason or another.