915is ECU fault

Measure the resistance of the #4 EGT Sensor.
It should be ~220 Ohms at Room temperature.
-50°C indicates Infinite (Open) Ohms.

Check for an OPEN Fuse in the FuseBox again.
The #4 EGT Circuit is shared with one of the Documented Fuses.
Likely F6, F8,  F10, or F16   But check them all just for completeness.

Swap your #4 EGT sensor with another cylinder.
If the fault moves to the other cylinder, The Sensor is bad.

If none of this works, Look for an Open Wire or Connection in the Harness.

HI

I checked Fusebox , all the Fuse were OK. 

its odd for me that all the EGT have error at the same time 

I checked the EGT connectors ( 4 pin connector ) ( 1=+5v , 2=EGT4,   3= EGT2   4=GND)

I send you a picture of EMU fault , 

What is the Thermistor  Drive ?

I'm waiting for your solution 

best regard 

I do not have a 915is to reference so I will make an educated guess.

With the Lanes powered up ...

Guess #1
If the EGT Sensors Do NOT share the #1 Pin on the connector.

EGT #4 is connected to pins 1 and 2 and EGT #2 is connected to Pins 3 and 4.
With your meter set to Ohms (Not Continuity);
On the Connector to the sensors:
Pins 1 to 2 should Measure ~210 Ohms at Room Temperature.
Pins 3 to 4 should Measure ~210 Ohms at Room Temperature.
On the Connector going to the ECU:
Pin 1 should measure +5V referenced to the Airframe Ground.
Pin 4 should measure +5V referenced to the Airframe Ground.

The connections might also be EGT 2 on 1 and 3, and EGT 4 on 2 and 4.
Use your powers of observation.

- - -

Guess #2
If the EGT Sensors DO share the #1 Pin on the connector. 

EGT #4 is connected to pins 1 and 2 and EGT #2 is connected to Pins 1 and 3. Pin 4 is the Shield.
With your meter set to Ohms (Not Continuity);
On the Connector to the sensors:
Pins 1 to 2 should Measure ~210 Ohms at Room Temperature.
Pins 1 to 3 should Measure ~210 Ohms at Room Temperature.
On the Connector going to the ECU:
Pin 1 should measure +5V referenced to the Airframe Ground.
Pin 4 should measure +0V referenced to the Airframe Ground.

Compare the readings on the 1/3 EGT connector to the 2/4 EGT Connector.

- - -
You are mixing what you are saying.
Are you reading EGT values off the ECU CAN-Bus using the BUDS Interface?
Or are you using a panel-mounted EMU?

- - -
The EGTs are high-tempThermistors.
The Thermistor Drive is the 5-volt power supply for the EGTs.
If the 5 Volt Thermistor Drive Power Supply Faults out,  ALL the EGTs will fail as a group.

- - -
There is also the option of swapping the 1/3 EGTs with the 2/4 EGTs to see if the fault moves to a different cylinder.

Bill, I think Marco is saying he has all four EGTs in fault, not just a fault on #4.  Look at the photo of the fault log he posted, its clearly a problem with the thermistor power supply. I’m guessing this is an internal ECU problem.  

Thank you Bill 

EMU and B.U.D.S show that all 4 EGT have error , I swap the 1,3 with 2,4 but nothing change.

next day I swap 1,3 with another engine and the problem solved.

its was interesting for me that when only 1,3 EGT have problem why all 4 EGT shows error??

Thank you so much and have a good time 

Happy new year