Snap-On EETA308D, Reference Manual

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6
3.6.2 Fuel Pump Current Measurement
Recommended Probe Setting: 20A
Note: Before taking measurements or clamping the
probe jaws around any wire, complete the Setup
steps below.
Setup
1. Use the On/Off and Range Selector switch to select
the 20A setting.
2. Perform the Low Amp Current Probe Zero
Adjustment procedure (refer to section 3.3).
Test
Important Note: If the vehicle has more than one fuel
pump, test each pump independently.
To measure fuel pump current:
1. Clamp the Low Amp Current Probe jaws around the
fuel pump voltage supply circuit near the fuel tank or
at the fuel pump relay.
2. Verify that the probe jaws are fully closed.
The fuel pump current readings display.
3. If a negative waveform displays, open the probe
jaws and clamp the probe in the opposite direction.
Humps in the waveform represent the condition of
the pump commutator and brushes (Figure 2).
Waveform humps are considered normal.
As brushes wear, the waveform will degrade, and the
pump speed may slow down (refer to Figure 3).
Figure 2 .
Figure 3 .