Hyundai Sonata LF: Engine Control System / Injector Troubleshooting
The three waveforms below are taken from the #1 and #4
injectors. The top waveform is from the high side (feed side) of the #1
and #4 injectors, while the middle waveform is from the low side (ground
side) of the #1 injector and the bottom waveform is from the low side
of the #4 injector.
The middle waveform is the same as the top waveform because
there is no ground for the circuit. With no current flowing in the
circuit, the #1 injector is not energized and fuel does not flow.
The bottom waveform shows that ground is supplied and there
is a voltage drop across the #4 injector. With current flowing in the
circuit, the #4 injector is energized and fuel flows.

Other information:
Repair procedures
Replacement
1.
Disconnect the negative (-) battery terminal.
2.
Remove the crash pad lower panel.
(Refer to Body - "Crash Pad")
3.
Remove the steering column upper & Lower shroud.
4.
Remove the ignition switch (A) and disconnecting the Key Warning / immobilizer connector...
Removal
Engine removal is not required for this procedure.
•
Use fender covers to avoid damaging painted surfaces.
•
To avoid damaging the cylinder head, wait until the engine
coolant temperature drops below normal temperature before removing it...