S-SERIES INSTRUMENTS
Testing
The diagnostic procedure outlined below can be followed
to
help
determine
the
cause
for
an
inoperative
pyrometer.
The component units (gauge and sender unit) are not
repairable. If tests indicate that a unit is faulty, replace it.
Before making diagnostic tests, inspect pyrometer wiring
circuits for damaged wires or loose or corroded
terminals. (Refer to vehicle wiring circuit diagrams in the
Service Manual.) Make any necessary repairs.
The pyrometer system can be checked with a volt-
ohmmeter (Simpson Model 260 or equivalent). Perform
tests in the following sequence to locate the problem.
1.
Disconnect leads from pyrometer gauge.
2.
Test sensor and cable assembly as follows:
a.
Set ohmmeter on Rx1 scale.
b.
Connect ohmmeter leads to sensor cable
terminals (Test 1, Figure 25).
c.
Ohmmeter should read 4 2 ohms (2-6 ohms).
d.
If specified ohmmeter reading is obtained,
sensor and cable are OK. Trouble is in
pyrometer gauge. Replace gauge.
e.
If ohmmeter reading is low (no resistance),
check for short in cable assembly.
f.
If ohmmeter reading is high (high resistance),
proceed to Step 3.
3.
Test sensor (thermocouple) as follows:
a.
Disconnect sensor leads from cable assembly.
b.
Connect ohmmeter to sensor lead terminals
(Test 2, Figure 25).
c.
Ohmmeter should read 1 ohm or less.
d.
If specified ohmmeter reading is obtained,
sensor is OK. Fault is in cable assembly.
Replace cable.
e.
If ohmmeter reading is high, sensor is faulty.
Replace sensor.
CTS-4140Y - Page 15
