To Check if the injectors are opening, use a mechanics stethoscope or a long blade screwdriver.

Touch the top of the injector body to get the best audibility. If the clicking sound is faint or absent,
the injector is not opening or partially opening.

Naturally you could take them for calibration by a professional as well. This is a DIY article as the checking & replacement of injector/s can
be done with no special tools & with a decent tech aptitude.

Take out the top shroud by removing the four 13mm ABS nuts.

Remove the injectors electrical connectors,

Pull off connector while pressing the thin metal clip. I used a flat screwdriver with a 10 mm wide blade.
It worked perfectly & pulled the connectors with a long nose pliers.

Remove the plug wires 2, 4 , 6, 8 frm the plug end only.

Take out the ground wire on the fuel rail passenger side witha 13mm wrench.

Take out the injector harness & move it to the driver side of the engine bay.

Take out the nut holding the fuel rail down on the EGR valve holding bolt with a 10mm socket.
Remove the vaccum line on the FPR & others as you see necessary,,,

Now is the time to get the area arnd the injectors clean so that you will not introduce dirt into the injector passages later on.

Start removing the fuel rail starting from the passenger end.

Press tabs holding the injectors in place & pull upward a little at a time simultaneously.
(wiggle the injectors a little while pulling them upward)

Start from 1 & 2 & proceed towards 7 & 8.

Once you have the fuel rail with the injectors out lift the pass. side end as much as possible ,
without excessive force. This will give you enough room to remove the injectors frm the fuel rail.

Now you must close the injector openings in the head. (I used facial tissue one @ each hole).

To take out the injector from the rail, take out the metal retainer clip. The retainer clip can be rotated for easier removal.

Once metal retainer clip is removed, you can wiggle the injector out of the fuel rail.
All injectors came out without the O-ring when I did.

To replace the injector in the rail, better have the O-ring replaced prior to inserting forcefully with a twisting motion & little lubricant..

Then replace the Metal retainer clip. It can be inserted from an easy angle then rotated to the correct position.

Once you have the injectors replaced. Do not be in a hurry to put the rail back.

Leave the injectors outside & turn the engine on (not turn over) to verify no leaks.

Once you verify or rectify any leaks replacing them is the reversal of this procedure,,

You can take out the harness connector & connect to a used injector & listen.
You will not hear a loud clicking in the absence of the fuel pressure on the pintle, but will hear a faint vibration only.

Also you can measure the voltage across the connector terminals,,,should be the same as battery voltage at the time.

DTC (Diagnostic Trouble Code) s related to INJECTOR / S

P0131 to P0155,,,,,,,,, O2 sensor related

P0171` to P0175,,,,,,,,,,fuel trim system

P0201 to P0208,,,,,,,,,,injectors 1 to 8 control circts