Service Manual

Fuel Lift Pump ISB, ISBe and QSB (Common Rail [...]
Page 5-32 Section 5 - Fuel System - Group 05
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Voltage will only be present when the lift pump is
commanded ON and when the lift pump is connected to
the harness. To measure lift pump voltage, use the
INSITE™ electronic service tool lift pump override test
and a breakout connector between the lift pump and the
engine harness
Check the voltage and resistance at the lift pump.
If the voltage does not meet the specifications, check the
power supply.
System Voltage
12-VDC 9-VDC (minimum)
24-VDC 21-VDC (minimum)
Two additional components that could possibly be
included on 24-volt systems are a relay and a voltage
regulator.
The 2-pin Deutsch™ connector for fuel lift pump signal
and return that attaches to the lift pump on 12-volt
systems instead connects to a 24-volt relay. The relay,
when switched ON by the ECM, delivers 24 volts from an
OEM-connected source to the voltage regulator. The
voltage regulator converts the 24-volt input to a 12-volt
output. The lift pump used is a 12-volt lift pump and
grounds through an OEM connection.
NOTE: On some 24-volt systems, the harness may have
been replaced by a service harness without a voltage
regulator. This service harness still uses the relay
switched by the ECM, but uses an alternate, un-switched,
12-volt source instead of the OEM supplied 24-volt
source.
Specifications
• The relay is located in the harness between the
voltage regulator and the OEM power supply on the
bottom edge of the ECM. The relay is switched ON for
60 seconds after the keyswitch is turned ON. It is also
switched ON anytime the engine is cranking or
running. The relay must provide 24 volts of power
output to the voltage regulator.
• The voltage regulator is located just below the ECM. It
receives 24 volts from the relay when the relay is
switched ON. The regulator provides 12 volts of power
output to the lift pump.
• A 12-volt lift pump is used in vehicles with a 24-volt
power system. It should run any time the relay is
switched ON, as described above.
If the output voltage of the voltage regulator is 24 volts,
the regulator has failed and must be replaced.