P0304 Code: Meaning, Symptoms, Causes & Fix

Overview

When P0304 appears, the control module has detected abnormal behavior related to Cylinder 4 Misfire Detected in powertrain controls.

Symptoms

rough operation in certain conditions
check engine light
increased fuel use

Common causes

Component failure in the monitored system affecting cylinder 4 misfire detected
Control module logic or calibration issue
Connector pin damage/corrosion or harness stress near related components

How to diagnose P0304

Confirm P0304 and capture freeze-frame data with a professional scan tool.
Inspect wiring, connectors, and grounds related to cylinder 4 misfire detected for obvious defects.
Use freeze-frame and live data to isolate whether the issue is electrical, mechanical, or control logic.
Check for related DTCs to identify the root-cause chain before replacing parts.
After repair, clear codes and confirm readiness monitors complete without recurrence.

Severity of code P0304

High: This code is high severity because the affected system can directly impact drivability, safety, or catalyst/engine protection.

Can you drive with P0304?

Driving with P0304 should be limited to a short trip for diagnosis/repair. Continued driving can cause expensive secondary damage.

If the warning lamp is flashing or drivability/safety is affected, avoid driving and diagnose immediately.

How to fix it (step-by-step)

Repair obvious wiring/connector faults first to prevent repeat parts replacement.
Address the root fault mode (generic) in the cylinder 4 misfire detected circuit/system.
Apply the required relearn/adaptation procedure if specified by service information.
Road-test and verify P0304 remains cleared under the conditions that originally set the code.

Fix options

Test component operation and replace if faulty.
Inspect circuit and connector condition.
Clear DTCs and verify with live data and completed drive cycle.

Typical repair cost

$400-$2000

Common mistakes when diagnosing P0304

Replacing parts without verifying voltage, ground, and signal integrity first.
Ignoring related stored/pending codes that indicate upstream faults.
Skipping post-repair verification drive cycle and readiness checks.

P0304 in common vehicles

P0304 appears across makes such as BMW, Mercedes-Benz, Audi, Volvo. Failure patterns differ by platform: wiring routes, software calibration, and component supplier revisions can change root cause.

Frequently asked questions

What causes P0304?

P0304 is commonly set by generic faults affecting cylinder 4 misfire detected.

How much does it cost to fix P0304?

For P0304, repair costs are typically $400-$2000 depending on exact root cause, labor rates, and part quality.

Can I clear P0304 without repair?

You can clear P0304 temporarily, but the code usually returns until the underlying fault is corrected.