What do i check too fix injector circuit 4 on cavalier 99

It means that the solenoid circuit that controls the valve internal to the injector has an open, or incomplete circuit. This means the injector cannot fire, thus no gasoline will get into the #4 cylinder. Usually, this problem is in the injector itself and is fixed by replacing the injector. It is possible, however, for the problem to be in the wiring to the injector from the ECM. In order to avoid buying an injector only to find that the wiring is bad, you can swap the suspect injector with one from another cylinder. If the fault changes to the other cylinder, change the injector. If the fault stays with the #4 injector, check the wiring.

"circuit open" means that the entire circuit, from the computer to the injector isn't making good connection. You will need to trace the wire all the way and find the break in the wire.

It's a fused circuit, so check the fuse, probably under hood, labeled injector. A shorted injector can shut down the injector drive circuit, so pull off all injector connectors, make sure fuse is good, then check for power to the injectors. Injector circuit should nave hot wire anytime key is on. Has constant voltage to injectors. When the computer internally grounds the injector ground wire, the injector will pulse.

Check the fuse for the injectors. If you have a test light, check for power to the injectors with key on. Pull off one injector connector to check for power. 2 wires to each injector-one is the power wire and powered anytime key is on. The other is the ground wire going into the computer, where it is internally grounded for a split second to pulse the injector-fuel is then sprayed out.
If power circuit is good, test the ground circuit: clip a test light lead to the POSITIVE POST of battery. Insert tester probe into the ground terminal of injector-the one that has no power with key on. Now have someone crank the engine over: test light should be blinking.
If both tests work-steady power to injectors with key on, and blinking tester on ground terminal with engine cranking, then the injector drive circuit and the ground circuit is working.
Let me know what you find. Good luck.

For fuel injection, usually the ground is inside the engine computer. The computer grounds the circuit for a split second to pulse the injectors. When key is on, the injector circuit has constant power to the injectors. When the computer grounds the circuit internally, the injector coil is energized, or pulsed.

Well code 204 means the computer has detected a high or low resistance in the circuit for injector number 4. The problem could be in the wiring harness or the injector itself.
The resistance of the injector would be checked first.

Why would you take any car to a dealership?

Never a car over 5 years old

PO271 Cylinder #4 Injector Circuit High

Take to a local repair shop

You won't have the ability to diagnose

The evidence suggests that you do indeed have a bad fuel injector. Inspect the wiring to make sure you don't just have a poor electrical connection there - then if that looks good replace the injector.

HI. One way to check which injector has the open circuit is to use an ohm meter.
With engine off disconnect each injector at a time and put the test leads of the ohm meter on the terminals of the injector, take a reading. The 4 readings should be approx. the same.
The injector at fault will show no reading ( open circuit)
So good luck with this test
Ps if you don`t have an ohm meter they are cheap to buy. you don`t need a profesional one
john

Still need the codes.
Injectors can go "bad" in a couple of different ways; all they are is an electromagneticaly controlled nozzle. When the ECU "fires" the injector, it pulses a ground circuit for 4-8 milliseconds, the electromagnet powers up, the valve at the bottom of the injector opens, and the fuel shoots out, under pressure. The wire can be bad/chafed/corodded/ The electromagnet may be weak. The nozzle may be stuck. Lots of things. But, to put in an injector for a number 4 cylinder misfire (p-0304 code) would be one of the last things that I would do.