Ford Transit 2002 Owner's Manual page 776

The IAT sensor output is useful if the engine being tested is cold or after an over-night cold
soak. The ECT sensor or CHT sensor and the IAT sensor should either indicate the same
value or be within 1 to 2 degrees Celsius of each other.
The ECT sensor output is important to display as it indicates the engine warm-up and
opening temperature for the thermostat. It will initially indicate a slightly higher reading
just before the thermostat opens and then drops back before settling to a near flat line
output (see graphic below).
Item Part Number
A -
B -
CAUTION: If the ECT sensor output reaches the 120ºC default line under normal
cooling system pressure, internal damage may be caused to the engine and a diagnostic
trouble code (DTC) will be set in the PCM. The test should be stopped and the cause
located and corrected. If the cooling system does not pressurize, the coolant will boil at
100ºC which may also damage the engine. CARRY OUT the Coolant Expansion Tank Cap
Pressure Test Component Test in this section.
If the WDS only allows the ECT sensor to be displayed in volts, refer to the following table
for corresponding Celsius values:
Volts
1.33
1.02
0.78
0.60
0.46
0.35
0.27
The CHT sensor output is useful to examine the cylinder head temperature rise during the
warm-up cycle and later during the normal light throttle cruise test. This sensor output may
vary between vehicles with manual transmission and vehicles with automatic transmission
and should be used for reference only.
The LOAD display is used for reference as it is necessary to maintain a stable load line
during the test. It is necessary to carry out the test under normal light throttle cruise
driving conditions and average loads, typically 40% to 70% of the load value.
The VSS output is used for reference but can help to identify misfires and sensors which fail
during the warm-up cycle.
The RPM display indicates the engine speed and can be compared with the DSRPM.
The DSRPM is the desired or calculated idle speed which the PCM commands the engine to
reach. If the thermostat opens too early (before the correct opening temperature has been
reached), the engine will not reach this value.
When using the WDS in data logger mode, the signals recorded should remain within the
Description
Thermostat opens
Thermostat settles into a cyclic open and closure pattern
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ºCelsius
60
70
80
90
100
110
120