Erratic exhaust temp readings!! HELP!!

[Hoopsville]

Hi All,

I’m getting irregular exhaust gas temperature readings from my EGT sensor upstream from the SCR cat. It jumps from what appears to be the correct value (it varies depending on operating temp) to -0.04 degrees, and back. I thought it was the sender but if I disconnect the sender, the CDU (as it’s supposed to) puts up an estimated value (for me last night is was 5 degrees higher) - however that value also jumps back and forth to -0.04 too!!!

Anyone experienced this?? Any ideas welcome.

I’m using Xentry via pass thru, and on Diagnosis > SCR > Temperatures > Actual Values.

Connection/wiring looks ok. I’ve tried the “teach in” process for the sensor on Xentry too.

Car is ‘13 W166 GL350 Bluetec

Thanks ++.
Hoopsville

 

[supernoodle]

I would be careful looking at values in engineering units when you know you've got a problem. As you've mentioned they can be replacement values. If the fault is sporadic it will ramp between them.

You should have sensor values in volts, they aren't subject to any processing and will give a better indication on what's going on. You can use a multimeter to read it too.

The sense pin will be pulled up internally to 5v. The EGT is connected between this and ground. At low temps EGT resistance is high, input will read close to 5v. As temp increases resistance drops, measured voltage at sense pin will reduce.