Exhaust Temperature Sensor Diagnosis

Hello,

I have a 2014 Sharan with a CFFB engine and 116,000 km on it that I currently own.
The particulate filter is no longer regenerating, and the engine is in emergency mode.
I noticed a weasel bite on the exhaust temperature sensor located in the exhaust manifold. However, the cable was still connected to some of the individual strands.
According to VCDS, the exhaust manifold temperature is 156 degrees at 2500 RPM when the engine is idling, which seems much too low to me. I'm measuring similar values both before and after the DPF.

Could it really be that one sensor fails and, as a result, the other two no longer provide accurate readings? I've read that all three sensors share a common ground connection in the power supply circuit.

How can the three sensors be safely diagnosed?

Thank you very much.
Thilo.

Hi,
"I would first obtain a wiring diagram to avoid having to make assumptions about common grounds, etc. In an older SSP, the sensors are individually connected to the STG (control unit), while in my RLF (radio location finder), they have a common line back to the STG (no common ground!)."
When the engine is cold, all temperature sensors should display ambient temperature. As the engine temperature increases, the temperature sensor on the exhaust manifold will heat up faster than the others. However, you cannot obtain accurate readings due to the engine running in a non-optimal state.
What does the error memory indicate? Is the wiring at least visibly in order now?
Of course, you can remove the sensors individually and test them with a hot air gun. However, I wonder if that's the right approach.
hg
Herbert.

Quote:

According to VCDS, the exhaust manifold temperature is 156 degrees at 2500 RPM when the engine is at idle.

Hello,

"It also seems a bit low to me, but it would be normal for an idle. If there's no load at 2500 rpm, it might also be possible."

The easiest way to check the temperatures is when the engine is cool. At that point, all sensors should display the same temperature, which should be approximately the ambient temperature.

Best regards, Rainer.

Evening.

Thank you for your responses.
The only error code stored is related to the DPF, indicating a lack of regeneration. I'll schedule a car scan for tomorrow.
Tomorrow, I will replace the exhaust sensor that was damaged by a badger. Before that, I want to be sure that I'm not wasting my time searching for something else.
After 24 hours of inactivity, the temperature readings were 20 degrees Celsius in the manifold, 16.5 degrees Celsius before the DPF (Diesel Particulate Filter), and 17 degrees Celsius after the DPF.

The owner had previously been to another workshop, and they mentioned something about the mass airflow sensor (MAF). However, they dismissed it immediately because they probably didn't see a way to make money from it. Also, either no error code was stored (deleted?), or they only looked at the values in the limp-home mode.
The last regeneration occurred at least 1400 km ago.

Good evening, Thilo,

After replacing the sensor, when measuring directly at the engine control unit (large connector), the resistance value between pin A9 and pin A89 should be between 90 and 100 kiloohms at 20 degrees Celsius.

The temperature sensor located before the diesel particulate filter, which should be connected from pin A32 to pin A89, should also be within this range.

The sensor located before the NOx sensor should have a resistance between 38 and 42 kiloohms, measured between pins A75 and A89.

There is a testing guide for the 3 sensors, which provides rough reference values at different temperatures. It is also possible to check the voltage values.

Best regards,

Michael.

Evening.

I replaced the sensor today and performed a stationary service regeneration.
Error memory is clear, the vehicle is running again.
The exhaust gas temperature during operation is between 450 and 550 degrees Celsius, and sometimes even higher.
I then reinstalled the old sensor, and the temperature doesn't rise above approximately 300 degrees.
So, the error was either actually caused by the weasel bite in the cable, or it could also be due to a defective sensor.


Sure, here's the translation:

"Vg" is an abbreviation for "very good." It is often used in online communication to express approval or agreement.
Thilo.

Thank you for the feedback .