P0355 Code: Cylinder 5 Ignition Coil Circuit Fault
Diagnostic trouble code P0355 is triggered when your vehicle’s engine control module (ECM) detects a malfunction in the ignition coil circuit for cylinder 5. This is a high-severity code that affects engine performance and can prevent proper spark plug firing. If you’re seeing this code, your engine is likely misfiring on cylinder 5, which can damage your catalytic converter and reduce fuel economy. Understanding what’s causing P0355 is essential for safe, reliable vehicle operation.
What Does P0355 Mean?
The P0355 diagnostic trouble code breaks down as follows:
- P = Powertrain system code
- 0 = Generic OBD-II code (applies to all manufacturers)
- 3 = Ignition system problem
- 55 = Cylinder 5 ignition coil circuit
This code specifically indicates that the ECM has detected an electrical fault in the ignition coil circuit responsible for firing the spark plug in cylinder 5. The fault could be an open circuit, short circuit, or the coil itself has failed. Modern vehicles use individual coil-on-plug (COP) ignition systems where each cylinder has its own ignition coil mounted directly on the spark plug. When the ECM cannot properly control or detect the operation of cylinder 5’s coil, it sets this code.
Note: Cylinder 5 location varies by engine configuration. In V6 engines, it’s typically on the passenger side. In V8 engines, it’s usually the fifth cylinder in firing order. Consult your vehicle’s service manual for the exact location.
Common Symptoms
When P0355 is active, you may notice one or more of the following symptoms:
- Check Engine Light (CEL) illuminated on the dashboard
- Engine misfires on cylinder 5, causing rough idle or hesitation during acceleration
- Loss of power and reduced engine performance
- Rough running at idle or low RPM
- Increased fuel consumption due to incomplete combustion
- Vibration felt through the steering wheel or seat
- Difficulty starting the engine (in severe cases)
- Smell of raw fuel from the exhaust (unburned fuel)
- Black smoke from the exhaust pipe
Possible Causes
P0355 can be caused by several issues, ranked from most to least common:
1. Faulty Ignition Coil Pack (Most Common)
The ignition coil for cylinder 5 has failed internally or has a broken connection. Coils wear out over time due to heat and electrical stress. This is the most common cause of P0355 and typically requires coil replacement.
2. Damaged or Corroded Wiring/Connectors
The electrical harness connecting the ECM to the cylinder 5 ignition coil may be damaged, corroded, or loose. Water intrusion, rodent damage, or poor connections can interrupt the signal.
3. Spark Plug Issues
A worn, fouled, or incorrectly gapped spark plug in cylinder 5 can cause the coil to work harder and trigger a fault code. However, this is less common than a coil failure.
4. Engine Control Module (ECM) Malfunction
In rare cases, the ECM itself may have a fault in the circuit that controls the cylinder 5 ignition coil. This is uncommon but possible if multiple ignition coils have been replaced without resolving the issue.
5. Ground Wire Problems
A loose or corroded ground connection for the ignition coil circuit can prevent proper electrical flow and trigger P0355.
6. Fuel Injector Issues
While less common, a faulty fuel injector on cylinder 5 causing chronic misfires can indirectly trigger ignition coil fault codes.
Diagnostic Steps
Follow these steps to diagnose the root cause of P0355:
Step 1: Scan for Additional Codes
Use an OBD-II scanner to check for other trouble codes. If you see P0300 (random misfire), P0301-P0308 (cylinder-specific misfires), or other ignition codes, this helps narrow down the problem.
Step 2: Visually Inspect the Cylinder 5 Ignition Coil
Locate the ignition coil for cylinder 5 (consult your service manual for location). Look for:
- Cracks or damage to the coil housing
- Corrosion or burn marks
- Loose or corroded connectors
- Oil leaks around the coil
Step 3: Check the Electrical Connector
Disconnect the coil connector and inspect for:
- Corrosion or oxidation on the pins
- Bent or damaged pins
- Loose or cracked connector housing
Clean the connector with electrical contact cleaner and reconnect firmly. Clear the code and test drive to see if it returns.
Step 4: Inspect Wiring and Ground Connections
Trace the wiring harness from the coil to the ECM. Look for:
- Damaged insulation or exposed wires
- Pinched or crushed wires
- Loose ground connections
- Signs of rodent or water damage
Step 5: Test the Ignition Coil
Use a multimeter to test the coil’s resistance:
- Primary resistance (coil terminals): typically 0.4–2 ohms
- Secondary resistance (coil to spark plug): typically 5,000–15,000 ohms
Consult your vehicle’s service manual for exact specifications. If readings are outside the range, the coil is faulty.
Step 6: Check the Spark Plug
Remove the spark plug from cylinder 5 and inspect it for:
- Excessive wear or erosion
- Carbon fouling (black deposits)
- Oil fouling
- Incorrect gap
Replace if necessary and ensure proper gap (typically 0.028–0.060 inches, depending on vehicle).
Step 7: Clear the Code and Test Drive
After making repairs, use your scanner to clear the P0355 code. Take the vehicle on a 10–15 minute test drive, including highway speeds and varying throttle inputs. If the code doesn’t return, the repair was successful.
Repair Cost Estimates
The cost to repair P0355 varies depending on the root cause and your vehicle:
- Ignition Coil Replacement: $150–$400 (parts and labor combined)
- Spark Plug Replacement: $50–$150
- Wiring/Connector Repair: $100–$300
- ECM Reprogramming/Replacement: $500–$1,500+ (rare)
- Diagnostic Service: $75–$150 (if you take it to a shop)
Money-Saving Tip: If you’re mechanically inclined, replacing an ignition coil is often a DIY job that takes 15–30 minutes. This can save you $100–$200 in labor costs.
Can I Still Drive?
P0355 is a high-severity code that requires prompt attention, but you may be able to drive carefully to a repair facility:
- Safety: The vehicle is drivable but not safe for extended highway driving. Engine misfires can damage the catalytic converter and reduce braking power.
- Performance: Expect reduced power, rough idle, and poor fuel economy.
- Emissions: The vehicle will likely fail an emissions test.
- Duration: Avoid driving more than a few miles until the issue is diagnosed and repaired.
Recommendation: Have the vehicle diagnosed and repaired as soon as possible. Continued driving with a misfiring cylinder can cause expensive damage to the catalytic converter, which costs $800–$2,500 to replace.
Frequently Asked Questions
Q: Can a bad spark plug cause P0355?
A: Yes, but rarely. A severely fouled or worn spark plug can cause misfires that stress the ignition coil, potentially triggering P0355. However, the coil itself is the most common culprit. If you replace the coil and the code returns, check the spark plug next.
Q: Will P0355 go away on its own?
A: No. P0355 is a persistent code that will not clear without repair. The underlying electrical or mechanical fault must be fixed. The code may temporarily disappear if you clear it with a scanner, but it will return when the fault is detected again.
Q: Can I drive with P0355 to the mechanic?
A: You can drive short distances (a few miles) to a repair facility, but avoid highway driving. Misfires can overheat and damage the catalytic converter. If the misfire is severe or the engine is running very rough, it’s safer to have the vehicle towed.
Q: What’s the difference between P0355 and P0356?
A: P0355 is for cylinder 5, while P0356 is for cylinder 6. Both codes indicate ignition coil circuit faults. The diagnostic and repair procedures are identical; only the affected cylinder differs. In V6 engines, you may see both codes if multiple coils are failing.
Q: How long does it take to replace an ignition coil?
A: Most ignition coil replacements take 15–45 minutes, depending on engine layout and accessibility. Some engines have coils that are easy to access; others require removing intake manifolds or other components. A professional mechanic can typically complete the job in under an hour.