129Section 8 Component Testing and AdjustmentTP-6356 4/12
8.9 Engine Pressure and
Temperature Sensors
8.9.1 General
Use this section to test engine sensors (switches or
senders) installed by the generator set manufacturer on
the engine. Refer to the respective engine service
manual for testing sensors installed by the engine
manufacturer.
Use the following tests to determine if the sensor is
functional. All sensors should have part numbers
stamped on the metal housing. In cases where the
number is illegible or missing, refer to the respective
generator set parts catalog for the corresponding part
number. The user must determine the sensor part
number in order to determine the sensor specifications
which are found in Section 1, Specifications.
The sensors can be installed on the generator set
provided the leads are disconnected and a temperature
or pressure gauge is available to determine the engine
values. Otherwise, remove the sensor after draining the
respective engine fluid (oil or coolant) and test using a
separate pressure or temperature source.
The resistance of the oil pressure and water
temperature sender output signals varies as the
respective pressure and temperature change. Use the
resistance change for verification of sender function.
Disconnect all leads from the sender before checking
resistance. If the sender functions and the gauge does
not function, check the engine wiring harness, leads,
and connectors before replacing the gauge.
Some generator sets may have senders/switches
incorporated with the engine ECM (electronic control
module). Identify engine ECM senders/switches by
lead designations listed in the following testing
information. Refer to the wiring diagrams manual for
additional lead identification information. Use the
engine service manual for troubleshooting ECM
senders/switches.
8.9.2 Sensor Types
The sensors referenced in this section typically provide
the following controller inputs:
D High engine temperature shutdown switch
D High engine temperature warning (prealarm) switch
D Low oil pressure shutdown switch
D Low oil pressure warning (prealarm) switch
D Low water temperature warning switch
D Oil pressure gauge sender (see Section 8.9.5)
D Water temperature gauge sender (see Section 8.9.6)
8.9.3 Switch Testing
Before testing switch, disconnect the switch lead(s).
Pressure Switch
Some pressure switches make contact on falling
pressure and some on rising pressure; refer to the
respective drawing for contact style. Connect an
ohmmeter to the switch terminals. Switches with one
terminal require connection to ground on the switch
metal body. Apply the pressure value shown in
Section 1.7, Pressure Switches, and observe the
ohmmeter before and after values to determine if the
switch contacts open and close per specifications.
Temperature Switch
High water temperature switches make contact on rising
temperature. Low water temperature switches make
contact on falling temperature. Refer to the respective
drawing for contact style. Connect an ohmmeter to the
switch terminals. Switches with one terminal require
connection to ground on the switch metal body. Apply
the temperature value shown in Section 1.6,
Temperature Switches, and observe the ohmmeter
before and after values to determine if the switch
contacts open and close per specifications.
8.9.4 Sender Testing
Before testing sender, disconnect the sender lead(s).
Pressure Sender
Pressure senders change resistance values as
pressure changes. Connect an ohmmeter to the sender
terminals. Senders with one terminal require
connection to ground on the switch metal body. Apply
pressure values shown in Section 1.4, Pressure
Senders, and observe the ohmmeter values to
determine if the sender changes resistance per
specifications.
Temperature Sender
Temperature senders change resistance values as
temperature changes. Connect an ohmmeter to the
sender terminals. Senders with one terminal require
connection to ground on the switch metal body. Apply
temperature values shown in Section 1.5, Temperature
Senders, and observe the ohmmeter values to
determine if the sender changes resistance per
specifications.
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