P0304 Mercedes-Benz Code - Cylinder 4 Misfire Detected
Quick Answer
When a misfire occurs, engine speed will fluctuate. Common causes include Faulty Spark Plug #4, Clogged or faulty Fuel Injector #4, Faulty Ignition Coil #4. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.
- What it means
- P0304 Mercedes-Benz indicates Cylinder 4 Misfire Detected.
- Common causes
- Common causes include Faulty Spark Plug #4, Clogged or faulty Fuel Injector #4, Faulty Ignition Coil #4.
- Severity
- High - diagnose this code as soon as possible.
- Can I drive?
- Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.
Code P0304 Mercedes-Benz Description
What are the Possible Causes of the DTC P0304 Mercedes-Benz?
- Faulty Spark Plug #4
- Clogged or faulty Fuel Injector #4
- Faulty Ignition Coil #4
- Fuel Injector #4 harness is open or shorted
- Fuel Injector #4 circuit poor electrical connection
- Ignition Coil #4 harness is open or shorted
- Ignition Coil #4 circuit poor electrical connection
- Insufficient cylinder 4 compression
- Incorrect fuel pressure
- Intake air leak
How to Fix the DTC P0304 Mercedes-Benz?
Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.
Code Tech Notes
What is the Cost to Diagnose the Code?
Labor: 1.0
To diagnose the P0304 Mercedes-Benz code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.
Need more information about the P0304 Mercedes-Benz code?
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Frequently Asked Questions about P0304 Mercedes-Benz Code
1. What does the OBDII code P0304 mean on a Mercedes-Benz?
P0304 indicates a misfire has been detected in cylinder 4 of your Mercedes-Benz's engine.
2. What are the common symptoms of a P0304 code in a Mercedes-Benz?
Symptoms may include a rough idle, loss of power, poor fuel economy, engine hesitation, or the Check Engine Light being illuminated.
3. What causes the P0304 code in a Mercedes-Benz?
Common causes include a faulty spark plug, bad ignition coil, clogged fuel injector, low compression in cylinder 4, or vacuum leaks near the cylinder.
4. Can I drive my Mercedes-Benz with a P0304 code?
Driving with a cylinder misfire can cause engine damage over time, so it’s best to address the issue as soon as possible.
5. How do I fix the P0304 code on my Mercedes-Benz?
Repairs may include replacing the spark plug or ignition coil in cylinder 4, cleaning or replacing the fuel injector, or addressing any compression or vacuum issues.
6. How can I confirm if the ignition coil is causing the P0304 code?
Swap the ignition coil from cylinder 4 with one from another cylinder. If the misfire moves to the other cylinder, the ignition coil is faulty.
7. Can bad fuel quality cause a P0304 code in a Mercedes-Benz?
Yes, poor-quality or contaminated fuel can lead to misfires, including in cylinder 4, and should be ruled out as a cause.
8. What tools are needed to diagnose a P0304 code?
You’ll typically need an OBDII scanner, a spark plug tester, and possibly a compression tester or fuel pressure gauge for a thorough diagnosis.
9. How much does it cost to fix a P0304 code in a Mercedes-Benz?
Costs vary depending on the issue, but replacing a spark plug or coil can range from $100–$300, while more complex repairs like addressing compression issues may cost significantly more.
10. Can a dirty air filter cause a P0304 code?
While not a direct cause, a clogged air filter can affect overall engine performance and contribute to conditions that lead to cylinder misfires.
Discuss the causes and fixes for P0304 Mercedes-Benz OBDII Code
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Cly 4 misfire. OBD also shows revs are within limits for crankshaft sensor to be working ok.
I swapped coil 4 for coil 3 with no difference to the cly 4 misfire. I the diconnected the coil 4 electric connection, no difference was observed.
It's my belief that the fault may be in the electrical wiring pack to the coils and in particular, cly 4. Can people please confirm whether my logic is ok or am I looking in the wrong place?
Plugs- done
New coils
Injectors test ok
Oil/air filters replaced
Cly 4 sometimes slightly below, around 10 bar.
Failure on emissions at idle but pass on higher revs, 2000+.
Car is MB CLK 200 Elegance AMG CONVERTIBLE. -
My 04 T1n has code 304 with rough engine and smoke/soot from exhaust. Suspect injector putting too much fuel in cylinder.
Did a leak down test and one of the 5 is 1/4" while others are equal at 1/2".
...waiting on replacement injector atm.
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