9
Test
To measure injector current:
1. Clamp the Low Amp Current Probe around the B+
side or the control side wire of injector. Do not
clamp the probe around both wires.
2. Verify that the probe jaws are fully closed.
The injector current readings display.
3. If a negative waveform displays, open the jaws
and clamp the probe in the opposite direction.
Tech Note
If injectors are difficult to access, it may be possible
to check injector current at the fuse box (if
applicable).
To check injector current at the fuse box:
1. Locate the fuse box and remove the injector fuse(s).
2. Install an inline fuse harness in place of the
fuse.
3. Clamp the Low Amp Current Probe around the
inline fuse harness.
On sequential fuel injected vehicles, each waveform
represents current flow through one injector. On bank-fired
injectors, each waveform represents current flow through
the injector bank. The injector waveform should have a
gradual rise or ramp as the current begins to flow through
the injector or the injector bank. Current flow through
each injector or injector bank should be about the same
(refer to Figure 6).
Figure 6.
If an injector or an injector bank has high current
flow, suspect a shorted injector (refer to Figure 7).
Figure 7.
If an injector peak is missing, suspect an open injector,
wiring, or defective PCM driver circuit (refer to Figure 8).
Figure 8.
To measure amperage, measure the maximum voltage
of the waveform and use 100 mV = 1A for calculation.
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