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P0204 means cylinder 4's injector circuit is open - no fuel is being delivered to that cylinder. You will almost certainly see a P0304 misfire code alongside this. On 4-cylinder engines, cylinder 4 is the last cylinder and its wiring runs the farthest from the PCM, making it more prone to wiring damage. See top-rated scanners on Amazon ↗
🗺️ Where Is the Problem?
Blueprint view - P0204 fault at fuel injector for cylinder 4 - open circuit, no fuel delivery
These are statistical causes across ALL vehicles - your exact car may rank differently
For example, on a Honda 4-cyl the downstream O2 sensor causes P0204 64% of the time, but on a GM 5.3L V8 the catalytic converter is the cause 71% of the time. Get a probability ranking built specifically for your year, make, model, and mileage.
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🎯 Top Causes & Probability
50%
#1 - Most Likely
Failed Cylinder 4 Injector
The internal solenoid coil of the cylinder 4 injector has broken open. Measure resistance at the injector - typical spec is 12–16 ohms. An open reading (OL/infinite) confirms a dead injector that must be replaced. Cylinder 4 is often the hottest-running cylinder, accelerating injector wear.
🔩 Part
$30–$150
👨🔧 Labor
$80–$200
⚡ DIY Difficulty
Medium
30%
#2 - Check First
Broken Wiring to Injector 4
Injector 4's wiring is typically the longest run in the harness and more susceptible to damage. Heat from the exhaust manifold near cylinder 4 can melt or crack insulation, causing a broken circuit. Inspect the harness near the exhaust manifold and any tight bends.
🔩 Part
$5–$30
👨🔧 Labor
$80–$200
⚡ DIY Difficulty
Medium
12%
#3 - Less Common
Corroded Connector
Moisture intrusion and road salt can corrode the injector 4 electrical connector, creating high resistance or an open circuit. Inspect the connector for green or white oxidation on the terminals. A thorough cleaning with electrical contact cleaner may resolve the code.
🔩 Part
$5–$30
👨🔧 Labor
$40–$80
⚡ DIY Difficulty
Easy
8%
#4 -
PCM Driver Failure
In rare cases the PCM's internal driver transistor for injector 4 fails, preventing pulse delivery. Confirm by verifying good injector resistance and continuity at the PCM connector before concluding PCM failure. A dealer or independent shop with factory diagnostics can confirm this quickly.
🔩 Part
$200–$800
👨🔧 Labor
$100–$200
⚡ DIY Difficulty
Hard
🚗 Most Affected Vehicles
🔧 Step-by-Step Diagnosis
- Measure Injector 4 Resistance - Unplug the injector 4 connector and check resistance across the two terminals. Typical spec is 12–16 ohms for port fuel injectors. "OL" (open loop) reading confirms a dead injector coil requiring replacement.
- Clean and Inspect Connector - Inspect the injector 4 connector for corrosion, moisture, or bent terminals. Spray with electrical contact cleaner, allow to dry, reconnect and retest before replacing parts.
📍 Find a Trusted Shop Near You
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Tips for Choosing a Shop
- Ask if they charge a diagnostic fee and whether it applies toward the repair
- Request a written estimate before approving any work
- Ask specifically about the part brand - OEM vs. aftermarket matters for this code
- Check Google reviews for recent mentions of the specific repair you need