P0204 code: Injector Circuit/Open - Cylinder 4
P0204 means injector Circuit/Open - Cylinder 4. The code says where to look, not what failed — the fix depends on which cause your car actually has.
What P0204 means
P0204 is the engine computer reporting that the cylinder 4 injector circuit isn't behaving electrically — it detected an open, a short, or resistance outside the expected window when it tried to pulse that injector. This code lives in the wiring-and-coil world, not the fuel-flow world: a clogged injector would not set it, because a clog doesn't change the circuit's electrical properties. In practice the fix is most often at the connector (corrosion, a loose terminal, or a plug knocked off during other work), next most often in chafed or broken harness wiring, and after that a failed winding inside the injector. The computer's own injector driver fails only rarely. Since cylinder 4 usually stops firing, the misfire code P0304 is a common companion.
P0204 symptoms
- Cylinder 4 misfire — P0304 frequently stored with this code
- Rough idle and vibration at stoplights
- Noticeable power loss; the engine feels flat
- Check-engine light, which can flash under an active misfire
- Longer cranking before startup on some engines
What it costs to fix P0204
Typical range: $80–$550 · about ~0.5–2 hrs of labor
| If the cause is… | Part | Labor |
|---|---|---|
| Fuel injector (single) | $50–$300 | ~0.5–2 hrs |
| Wiring / connector repair | $10–$60 | ~0.5–1.5 hrs |
On most inline four-cylinder engines cylinder 4's injector is easy to reach, keeping labor low. V engines that require intake-manifold removal push labor toward the high end. These ranges cover typical gasoline port and direct-injection engines; diesel injectors cost several times more.
The price swings on which cause it turns out to be — so confirm the cause before paying. Diagnose P0204 for my exact vehicle →
How to fix P0204
Moderate — doable at home with common tools and patience
- Confirm only cylinder 4 is affected
Pull the full code list. P0204 with P0304 and nothing else keeps the hunt on cylinder 4. If you smell raw fuel or the engine floods, the control wire may be shorted to ground and holding injector 4 open rather than dead — stop cranking and find the short before running it further.
- Inspect the end-cylinder harness run
On many four-cylinder engines cylinder 4 is the end cylinder nearest the transmission, and its harness branch can pass close to the exhaust manifold, a lifting bracket, or the dipstick tube. Look for melted insulation, a rubbed-through loom, and a connector baked brittle by heat.
- Compare injector 4 against the other three
Measure across injector 4's pins with the connector off, then measure injectors 1 through 3 the same way. On a healthy engine they read nearly identical, typically in the low-to-mid teens of ohms for high-impedance types; an outlier or open reading on injector 4 condemns it without further guesswork.
- Check for voltage drop on the feed
With the connector plugged back in and the engine running, back-probe the feed terminal at injector 4 and compare it with battery voltage. A difference of more than a few tenths of a volt means resistance in the feed — a corroded splice or a tired connector — that can trip the code even with a good injector.
- Replace the injector or repair the circuit
A failed winding means a new injector with fresh O-rings and a leak check under key-on pressure before starting. A damaged wire gets a soldered, heat-shrunk repair routed away from whatever cooked it. If both pass, an engine-computer driver fault is possible but should be the last conclusion.
DIY or shop? Most cylinder 4 circuit faults turn up with a multimeter and a careful look at the harness near the end of the engine, which is reasonable home-mechanic work. Replacing a port injector is a moderate job; a direct injector is not, because the high-voltage drive circuit and the special seals and pullers make it a shop task. Hand it over too if the engine is flooding or the tests lead back to the engine computer.
Tools for the DIY steps: Digital multimeter · Back-probe pins · Flashlight · Fuel injector O-ring kit · Heat-resistant wiring loom
Not sure which step applies to your car? Get the likely cause for your exact vehicle before buying anything for P0204.
Start a case with P0204 and your car. Redline weighs these causes against what your car shows, and names the check that would settle it before you buy parts.
Can I drive with P0204?
Redline can’t determine from a symptom or code alone whether your car is safe to drive.
P0204: common questions
I have both P0204 and P0304 — which do I fix?
They're two views of the same problem: P0204 is the electrical fault on the cylinder 4 injector circuit, and P0304 is the misfire that results when that cylinder gets no fuel. Repair the circuit fault and the misfire code should clear with it.
What's the first thing to check for P0204?
The injector connector. Unplug it, look for green corrosion, spread terminals, or a plug that wasn't fully clicked in — especially if anyone recently worked on the engine. It's the most common cause and the cheapest fix.
Is it okay to drive with P0204?
Not something a code can answer by itself. The bigger cost is feeding raw fuel to the catalytic converter, which can be ruined by a sustained misfire, so get it repaired promptly. A flashing light means active converter damage — stop driving.
What will fixing P0204 cost?
Often very little — connector and wiring repairs are cheap. If the injector itself has failed, expect a moderate part price plus half an hour to two hours of labor, with V engines that need the intake removed sitting at the top of that range.
Related trouble codes
Don’t have a scanner yet? A ~$25 Bluetooth adapter reads codes like P0204 from your phone. See our guide to the best OBD2 Bluetooth adapters. Run a repair shop? See Redline for shops.
Generic OBD-II reference. Manufacturer-specific behavior varies. Confirm with a scan tool and, for safety-related codes, a professional inspection. Cost ranges are reference ranges, not quotes.
Seeing P0204 on your car?
Every problem becomes a Case. Tell Redline what the car is doing: it shows what the evidence supports, what’s still missing, and what to check next, before you approve a repair.
“Inner pad ~1 mm. Outer pad 3 mm.”
Next: check the slide pins move freely before buying parts.