OBD2 Diagnostic Code
P0204
Injector Circuit Malfunction (Cylinder 4) — Repair Steps & Cost Guide
P0204 looks scary — but the actual injector itself is the last thing to replace. Before a shop quotes you a new injector, you need to know that a broken wire or a corroded connector causes this code far more often. Start cheap, work up.
Severity
8 / 10
High. Cylinder 4 misfires dump raw fuel into your catalytic converter. Do not delay.
Safe to Drive?
No — Limit Use
Short necessary trips only. Extended driving risks catalytic converter damage, which costs far more than fixing the injector circuit.
Typical DIY Fix Cost
Low – High
Wide range. A wiring repair costs very little. A new injector is moderate. Always diagnose before ordering parts.
🔍 What This Code Means
Your engine uses a fuel injector in each cylinder to spray precisely timed bursts of fuel into the combustion chamber. P0204 means the ECU (your car's main computer) detected a problem in the electrical circuit controlling the injector for cylinder 4 — not necessarily that the injector itself has failed.
Each injector is powered and grounded through a dedicated circuit. The ECU monitors voltage and current on that circuit constantly. When it sees a reading outside the expected range — too high, too low, or an open circuit — it sets P0204 and cuts power to that injector to protect the engine.
💡 P0204 is a circuit fault code, not a component fault code. It tells you the injector's electrical circuit has a problem. The cause could be the wiring, the connector, the injector itself, or in rare cases, the ECU driver circuit. Work through them in that order.
Cylinder 4 location varies by engine layout. On most inline 4-cylinder engines it is the rearmost cylinder. On V6 and V8 engines the numbering follows manufacturer convention — consult your vehicle's firing order diagram if you are unsure which cylinder to locate.
⚡ Common Symptoms
When cylinder 4 is not firing, you will usually feel it. The symptoms range from subtle to unmistakable depending on how many cylinders your engine has and how long the fault has been active.
Rough, lumpy idle
One dead cylinder causes a distinctive uneven shake at a stop. The engine rocks or vibrates more than normal — noticeably worse on 4-cylinder engines than on V8s.
Misfire feel under acceleration
Hesitation, stumble, or a brief surge when pressing the throttle from low speed. The power delivery feels uneven rather than smooth.
Strong fuel smell from exhaust
Raw unburned fuel exits through the exhaust. If the smell is noticeably stronger than usual, cylinder 4 is likely not firing at all.
Reduced power overall
Losing one cylinder means losing a meaningful percentage of total power. Especially obvious on 4-cylinder engines where cylinder 4 represents 25% of output.
Worsening fuel economy
The ECU adds fuel to compensate for the misfiring cylinder, and the catalytic converter works harder. Both hurt MPG.
Check engine light only
On some V6 and V8 engines with a healthy power reserve, drivability feels near-normal. The scanner code may be the first sign anything is wrong.
⚠️ If you also see P0300 (random misfire) alongside P0204, cylinder 4 is definitely not firing — it is not just a circuit reading issue. The injector circuit fault is actively causing the misfire.
🎯 Most Likely Causes
Ranked from most common to least common. Most P0204 repairs never go past cause #3. Start at #1 before spending anything.
1
Damaged or corroded injector wiring harnessThe wire leading to the cylinder 4 injector develops a break, a short to ground, or a corroded section — often at a bend point, a heat-exposed section near the exhaust manifold, or where it passes through a harness clip. The ECU sees an open or short circuit and logs P0204. This is the root cause in roughly 4 out of 10 verified cases.
~ 38% of cases
2
Faulty or corroded injector electrical connectorThe two-pin connector at the injector itself develops corrosion on the terminals, cracks in the housing that allow moisture in, or a terminal that has backed out of the connector body. Unplug it, inspect the pins, and push the connector back firmly — this alone resolves a surprising number of P0204 cases without any parts purchase.
~ 30% of cases
3
Failed fuel injector (open or shorted coil)The injector itself has a solenoid coil inside. That coil can fail open (no electrical continuity) or shorted (resistance far outside spec). A healthy injector reads 12–17 ohms on a multimeter across the two terminals. Outside that range confirms injector failure. This is the actual cause in about 20% of P0204 cases — not the starting assumption.
~ 20% of cases
4
Injector fuse or relay faultSome vehicles use a fuse or relay dedicated to the injector circuit. A blown fuse breaks the power supply to all injectors on that circuit — check your fuse box layout. This is quick to verify and costs nothing to check.
~ 7% of cases
5
ECU injector driver circuit failureInside the ECU, each injector is driven by a dedicated transistor or driver chip. When that driver fails, the circuit appears dead even though the wiring and injector are fine. This is rare and expensive to fix — confirm it only after all wiring, connector, and injector tests come back clean. Roughly 5% of P0204 cases reach this diagnosis.
~ 5% of cases
🔧 What to Check First
These three steps require no special tools, cost nothing, and eliminate the two most common causes before you spend anything on parts. Do them in order.
1
Unplug and inspect the cylinder 4 injector connectorLocate the fuel injector on cylinder 4. Unplug its two-wire connector and look at the terminals with a flashlight. You are looking for green or white corrosion on the metal pins, bent or pushed-back terminals, or cracks in the plastic housing. Clean corroded pins with electrical contact cleaner and a small pick. Push the connector back until it clicks firmly. Clear the code and drive — this resolves a large percentage of P0204 cases immediately.
2
Trace the injector wiring harness from the connector to the ECUWith the engine off, follow the wiring harness back from the cylinder 4 injector. Look for sections where the insulation has melted, chafed against a metal edge, or cracked from heat exposure near the exhaust manifold. Gently flex the harness at bends while watching your scanner — if the code clears momentarily when you flex the wire in a certain spot, you have found the break. A broken wire can be repaired with solder and heat-shrink tubing for very little cost.
3
Test the injector coil resistance with a multimeterSet your multimeter to Ohms (Ω). Unplug the injector connector and touch the probes to the two metal terminals on the injector itself — not the connector. A healthy injector reads 12–17 ohms. An open coil reads OL (overload / no continuity). A shorted coil reads near zero. Either extreme means the injector has failed internally and needs replacement. If the reading is within spec, the injector coil is fine and the fault is in the wiring or connector.
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⚠️ Common Misdiagnosis
P0204 has a clear name — "Injector Circuit" — and that misleads plenty of shops into jumping straight to the most expensive fix. These are the three traps most likely to cost you money unnecessarily.
⚠ Misdiagnosis #1 — New injector ordered before checking the wiring and connector
The code says "injector circuit." A large proportion of shops hear "circuit" and order a replacement injector immediately. But the connector and wiring account for the majority of P0204 cases. Any shop that quotes you a new injector without first showing you connector inspection and a multimeter resistance test is skipping the diagnostic work. That is not a service — it is guesswork with your money.
Potential savings: Injector part cost plus labor
⚠ Misdiagnosis #2 — Replacing all four injectors as a set
Some shops recommend replacing all injectors as a preventive set when one is suspected of failure. Unless the vehicle has extremely high mileage and the other injectors are already showing symptoms or out-of-spec resistance readings, this is unnecessary. P0204 is a single-cylinder fault. Diagnose the fault, fix what is broken, and move on.
Potential savings: Cost of three injectors plus additional labor
⚠ Misdiagnosis #3 — ECU replacement recommended without proper injector circuit testing
ECU driver failure is real but rare — roughly 1 in 20 P0204 cases. Before anyone recommends ECU repair or replacement, the wiring must be tested with a wiring diagram, the connector must be inspected, and the injector must be bench-tested or swapped with a known-good unit. If none of those steps have been performed, an ECU diagnosis is premature.
Potential savings: ECU replacement or reprogramming cost
💰 Estimated Repair Cost
DIY cost = parts only. Shop cost = parts plus labor. Ranges vary by vehicle, region, and shop rate. Use these as a planning guide — not a fixed quote.
Injector connector replacement / repair
DIYVery Low
ShopLow
LevelEasy
Injector wiring harness repair (splice / patch)
DIYMinimal
ShopLow–Moderate
LevelEasy–Moderate
Injector fuse replacement
DIYMinimal
ShopVery Low
LevelVery Easy
Single fuel injector replacement (cylinder 4)
DIYModerate
ShopModerate–High
LevelModerate
Injector wiring harness (full replacement)
DIYModerate
ShopHigh
LevelAdvanced
ECU injector driver repair / ECU replacement
DIYNot Advised
ShopVery High
LevelProfessional
✅ In the majority of P0204 cases, the total repair cost stays very low when you start with the connector inspection and wiring check. Most cars are fixed before the injector itself is even considered.
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🚗 Most Reported On
P0204 can appear on any fuel-injected gasoline vehicle. These models generate the most verified repair reports and owner discussions for this specific code.
Ford F-150 (2011–2019, 5.0L V8)
Dodge Ram 1500 (2009–2018, 5.7L Hemi)
Chevy Silverado (2007–2016, 5.3L V8)
Toyota Tacoma (2005–2015, 4.0L V6)
Jeep Grand Cherokee (2011–2017, 3.6L V6)
Honda CR-V (2007–2016, 2.4L)
Ford Explorer (2013–2019, 3.5L EcoBoost)
GM 4.8L / 5.3L / 6.0L LS engines (various)
❓ Frequently Asked Questions
Can I drive with P0204 active?
Short distances only and with real caution. Cylinder 4 is not firing correctly, which means raw unburned fuel is going straight into your exhaust and catalytic converter. Extended driving with P0204 active can permanently damage the catalytic converter — a repair that costs significantly more than fixing the injector circuit. Get it looked at quickly.
Why does P0204 keep coming back after I clear it?
Clearing the code removes the warning light, not the underlying circuit fault. The ECU will re-detect the problem within one or two drive cycles and set the code again. The physical fault — whether it is a broken wire, a corroded connector pin, or a failed injector coil — must be found and physically repaired before the code stays away for good.
Can a bad injector connector cause P0204 without the injector being faulty?
Yes, and this is actually one of the most common causes. A corroded pin, a cracked connector housing, or a terminal that has backed out of the connector body breaks the circuit just as effectively as a dead injector coil. Always inspect and clean the connector, and push it firmly back onto the injector before condemning the injector itself. Many vehicles are fixed at this step alone.
What resistance should a healthy injector read on a multimeter?
Most port fuel injectors used in modern gasoline engines read between 12 and 17 ohms across the two terminals. This is the high-impedance range used by the vast majority of passenger vehicles. Some older or performance-oriented applications use low-impedance injectors, which read 2 to 5 ohms. Always check your vehicle's specific service data for the correct specification — a reading outside the expected range confirms internal injector failure.
If P0204 and P0300 appear together, what does that mean?
P0300 is a random/multiple misfire code. When it appears alongside P0204, it confirms that cylinder 4 is actively misfiring — it is not just that the ECU sees a questionable circuit reading while the cylinder fires normally. The injector circuit fault is preventing fuel delivery to that cylinder. This combination makes the diagnosis straightforward: track down the wiring or connector fault and fix it. The misfire code will clear once the circuit is repaired.
🔗 Related Codes
These codes share similar root causes or commonly appear alongside P0204.
This guide is for informational purposes only. Always consult a qualified mechanic before performing any vehicle repair. OBDPlatform is not responsible for actions taken based on this content.