So what does the diagnostic system do?
The probe diagnosis page indications are in
green for normal readings and red for readings
that fail the criteria set at the bottom of the
Each temperature probe consists of two wires, a
positive lead and a negative lead. The two
numbers next to each identifier show the
resistance in Ohms of each lead.
For example, the line EGT1 8 3 means the
positive lead of the EGT1 probe has 8 Ohms
resistance, and the negative lead has 3 Ohms
When the probe is new, it will have relatively
As the probe ages, it’s resistance will slowly
go up. Eventually, the probe will measure
outside the pas/fail criteria you set at the
bottom of the screen, and change from green to
red, indicating that the probe should be
replaced before it fails and leaves you with no
temperature reading at all.
One other point to consider is that the longer
the wiring to the probes, the higher its
Every foot of EGT wire adds 1.7 Ohms/ft for the
+ lead and 0.8 Ohms/ft for the - lead. Every
foot of CHT wire adds 0.8 Ohms/ft for the + lead
and 1.2 Ohms/ft for the - lead.
A 24 ft harness will fail the criteria that an 8
ft harness will pass with. That is why we allow
the user to modify the pass/fail criteria on the
bottom of the screen.
The meaning of the
pass/fail criteria is as follows:
R MAX sets the maximum resistance (in Ohms) that
any single lead may have. If the R MAX is set to
20 Ohms a probe with either the positive or
negative leads measuring greater than 20 Ohms
will be annunciated in RED, otherwise its
displayed in GREEN.
R DIF sets the maximum resistance (in Ohms) that
the positive lead may differ from the negative
lead. If R DIF is set to 10 Ohms, the positive
and negative leads need to measure within 10
Ohms of each other to be annunciated in GREEN,
otherwise its RED.
Proper setting on G1234 with 8, 10, 14 foot
harness should be R
R DIF 10
Proper setting on G1234 with 20, 24 foot harness
R MAX 25
R DIF 15
Proper setting on G1234 with 30, 35 foot harness
R MAX 30
R DIF 20