P0204 OBD Code: Injector Circuit/Open – Cylinder 4 – Causes, Symptoms & Fixes

When your vehicle’s onboard diagnostic system detects trouble code P0204, it means the engine control module (ECM) has identified a problem with the fuel injector circuit serving cylinder 4. This code falls under the fuel system category and can range from a simple electrical connection issue to a completely failed injector. Understanding what this code means and how to diagnose it is essential for restoring proper engine performance and fuel efficiency.

What Does P0204 Mean?

P0204 is a generic OBD-II diagnostic trouble code that stands for “Injector Circuit/Open – Cylinder 4.” The code indicates that the engine control module has detected an electrical fault in the fuel injector circuit for the fourth cylinder. This could mean:

• The fuel injector itself is faulty or has failed
• The wiring harness connected to the injector is damaged, corroded, or loose
• The injector connector is disconnected, cracked, or corroded
• The fuel injector driver circuit in the ECM is malfunctioning
• An open circuit exists in the injector’s electrical pathway

The ECM continuously monitors the fuel injector circuits to ensure they’re functioning properly. When it detects that cylinder 4’s injector isn’t responding as expected—typically by measuring voltage or resistance—it sets this code and illuminates the check engine light.

Common Symptoms

Drivers experiencing P0204 may notice one or more of the following symptoms:

• Check Engine Light: The most obvious indicator; the light will remain illuminated until the code is cleared or the issue is resolved
• Engine Misfire: A noticeable hesitation, stumbling, or rough idle, particularly when cylinder 4 isn’t receiving fuel
• Loss of Power: Reduced acceleration and overall engine performance
• Rough Idle: The engine may shake or vibrate at a stoplight or when parked
• Poor Fuel Economy: The vehicle may consume more fuel as the engine compensates for the misfiring cylinder
• Difficulty Starting: In some cases, the engine may be slow to start or require multiple attempts
• Fuel Smell: Unburned fuel may create a strong smell from the exhaust

Possible Causes (Ranked by Frequency)

1. Faulty Fuel Injector (Most Common): The injector for cylinder 4 has internally failed, become clogged, or lost its electrical connection. This is the most common cause of P0204.
2. Loose or Corroded Injector Connector: The electrical connector on the fuel injector may be loose, corroded, or partially disconnected, breaking the circuit.
3. Damaged Injector Wiring Harness: The wires leading to the injector may be cut, pinched, corroded, or damaged by heat, creating an open circuit.
4. Fuel Injector Relay Failure: If the vehicle uses a fuel injector relay, a faulty relay can prevent power from reaching the injector circuit.
5. ECM Injector Driver Circuit Fault: The fuel injector driver circuit within the engine control module itself may be malfunctioning, though this is less common.
6. Blown Fuel Injector Fuse: A blown fuse in the fuel injector circuit will prevent power from reaching the injector.
7. Poor Ground Connection: A faulty ground connection at the injector or in the fuel injector circuit can cause the code to set.

Diagnostic Steps

Follow these steps to diagnose P0204 on your vehicle:

Step 1: Scan the Vehicle

Use an OBD-II scanner to confirm code P0204 and check for any additional related codes (such as P0201, P0202, P0203, or P0205). Multiple injector codes may indicate a fuel pump issue or relay problem rather than individual injector failures.

Step 2: Visual Inspection

Locate cylinder 4’s fuel injector and inspect:

• The injector connector for corrosion, cracks, or looseness
• The wiring harness for cuts, pinches, or heat damage
• The injector itself for signs of fuel leaks or damage
• Any burnt or melted insulation on nearby wires

Step 3: Test the Injector Connector

With the key off, disconnect the fuel injector connector for cylinder 4. Use a multimeter to check for:

• Resistance: A healthy fuel injector typically reads 12-16 ohms. If the reading is infinite (open circuit) or very low, the injector is faulty.
• Voltage: With the key on (engine off), check for voltage at the connector. You should see approximately 12 volts on one terminal.

Step 4: Check the Wiring and Connectors

Inspect the wiring from the ECM to the injector:

• Look for damaged insulation or corrosion
• Test for continuity between the injector connector and the ECM using a multimeter
• Check the ground connection at the injector

Step 5: Test the Fuel Injector Relay and Fuse

Locate the fuel injector relay and fuse in your vehicle’s fuse box (consult your owner’s manual for location). Check if the fuse is blown and test the relay for proper operation.

Step 6: Perform a Fuel Injector Pulse Test

Using a fuel injector tester or a scanner with live data capability, command the ECM to pulse the cylinder 4 injector. Listen for a clicking sound from the injector. If you don’t hear a click, the injector or its circuit is faulty.

Step 7: Replace or Repair as Needed

Based on your diagnostic findings:

• If the injector shows an open circuit (infinite resistance), replace it
• If the connector is corroded or loose, clean and reseat it
• If the wiring is damaged, repair or replace the harness
• If the relay or fuse is faulty, replace it

Repair Cost Estimates

The cost to repair P0204 varies depending on the underlying cause:

• Fuel Injector Replacement: $150–$400 per injector (parts and labor combined). OEM injectors are typically more expensive than aftermarket alternatives.
• Injector Connector Repair: $50–$150. If the connector is simply corroded or loose, cleaning and reseating may resolve the issue at minimal cost.
• Wiring Harness Repair: $100–$300, depending on the extent of damage and labor required.
• Fuel Injector Relay Replacement: $50–$150, including parts and labor.
• Fuse Replacement: $10–$30. This is the least expensive fix if a blown fuse is the culprit.
• ECM Reprogramming or Replacement: $500–$1,500+. Required only if the ECM’s injector driver circuit is faulty, which is rare.

Note: Labor costs vary by location and shop. Independent mechanics typically charge less than dealerships, but dealerships may offer warranty coverage on repairs.

Can I Still Drive?

The safety of driving with P0204 depends on the severity of the issue:

Short-term (a few miles): In most cases, you can safely drive a short distance to a repair shop. The vehicle will run on the remaining three cylinders, though performance will be noticeably reduced.

Extended driving: It’s not recommended to drive long distances with P0204 active. Continued misfiring can:

• Damage the catalytic converter due to unburned fuel entering the exhaust
• Cause further engine damage if the underlying issue worsens
• Reduce fuel economy significantly
• Make the vehicle difficult to control in certain driving conditions

Severity Assessment: P0204 is generally considered a moderate-severity code. While it won’t cause immediate catastrophic failure, it should be diagnosed and repaired as soon as possible to prevent secondary damage and maintain vehicle reliability.

Frequently Asked Questions

Q: Will P0204 clear on its own?

A: No, P0204 will not clear on its own. The code will remain stored in the ECM until either the underlying issue is repaired or the code is manually cleared with a diagnostic scanner. Even if the code is cleared, it will return if the problem persists.

Q: Can a bad fuel pump cause P0204?

A: While a bad fuel pump typically causes codes like P0087 (Fuel Rail Pressure Low) or P0088 (Fuel Rail Pressure High), a severely failing fuel pump can cause multiple injector codes, including P0204. If you see multiple injector codes (P0201–P0206), check the fuel pump pressure first before replacing individual injectors.

Q: Is P0204 the same as a misfire code?

A: No, they’re different. P0304 is a cylinder 4 misfire code, while P0204 is specifically an injector circuit fault. However, P0204 often causes a misfire in cylinder 4, so you may see both codes. The injector circuit fault is the root cause, and fixing it should resolve the misfire.

Q: Can I replace the fuel injector myself?

A: Fuel injector replacement is moderately difficult and varies by vehicle. If you have mechanical experience and the right tools, you can replace it yourself and save on labor costs ($100–$200). However, if you’re not comfortable working on fuel systems, it’s best to have a professional handle it. Always disconnect the fuel pump relay and relieve fuel pressure before starting work.