P0355 Ford F150 – Solving Cylinder 5 Ignition Circuit Malfunctions
A P0355 code on your truck indicates a primary or secondary circuit malfunction in ignition coil “E,” which corresponds to cylinder 5. This guide provides a professional walkthrough to diagnose wiring faults, test your coil-on-plug system, and fix the root cause of your engine misfire.
You are cruising down the road when your truck suddenly stumbles, the check engine light begins to flash, and you feel a distinct loss of power. Dealing with a p0355 ford f150 error can be frustrating, especially when your reliable workhorse starts acting like it wants to quit on you.
I understand the urge to just buy a new set of spark plugs and hope for the best, but this specific code usually points toward a deeper electrical issue than just a worn-out plug. We are going to look at the ignition system in detail to ensure you do not waste money on parts you do not actually need.
In the following sections, I will guide you through a professional-grade diagnostic process to identify whether the problem lies in the coil, the wiring harness, or the Powertrain Control Module (PCM). By the end of this article, you will have a clear plan to restore your Ford’s performance and clear that nagging light for good.
Understanding the p0355 ford f150 Diagnostic Trouble Code
The P0355 code is specifically related to the ignition coil “E” primary/secondary circuit. In the Ford world, “Coil E” refers to the ignition coil located on cylinder 5. This is not just a simple misfire code like a P0305; it means the PCM has detected an electrical continuity issue within the circuit that fires that specific coil.
On most Ford F150 engines, including the 5.0L Coyote and the older 5.4L Triton, cylinder 5 is the first cylinder on the driver’s side (front of the engine). Knowing the exact location is the first step in avoiding a wild goose chase under the hood. The PCM monitors the “driver” circuit for each coil, and if it does not see the expected voltage drop when the coil fires, it triggers this fault.
Unlike a standard misfire, which could be caused by fuel or compression, a P0355 is almost always purely electrical. This means we need to focus our attention on the coil-on-plug (COP) unit, the connector, the wiring loom, and the computer itself. Let’s break down exactly how to approach this systematically.
The Difference Between P0305 and P0355
It is easy to confuse these two, but the distinction is vital for your repair strategy. A P0305 means the computer detected that cylinder 5 is not contributing power, often due to a fouled spark plug or a vacuum leak. However, a p0355 ford f150 code specifically identifies a failure in the electrical circuit that controls the coil.
If you see both codes simultaneously, the electrical failure (P0355) is causing the misfire (P0305). Always fix the circuit code first. In many cases, once you resolve the electrical break, the misfire code will vanish on its own after a few drive cycles.
Common Symptoms of a Cylinder 5 Circuit Failure
When your truck registers this fault, the symptoms are usually impossible to ignore. Because the ignition coil is not firing correctly, the engine is essentially running on one less cylinder. This creates an unbalanced rotation that you will feel through the steering wheel and seat.
- Severe Engine Hesitation: You will notice a “chugging” sensation, especially under load or when accelerating onto the highway.
- Flashing Check Engine Light: A flashing MIL (Malfunction Indicator Lamp) signifies a catalyst-damaging misfire, which is common with ignition circuit failures.
- Poor Fuel Economy: The PCM may attempt to compensate for the dead cylinder by adjusting fuel trim, leading to a noticeable drop in MPG.
- Rough Idle: At a stoplight, the truck may shake or feel like it is about to stall.
If you are an off-roader or someone who hauls heavy trailers, these symptoms are even more pronounced. Attempting to climb a steep grade or pull a load with a dead ignition circuit can put excessive strain on your remaining cylinders and overheat your catalytic converter.
Top Causes for the P0355 Code in Ford Trucks
Identifying the “why” is just as important as the “how.” In my experience working on F-Series trucks, the causes for a p0355 ford f150 fault usually fall into three main categories. Understanding these will help you narrow down your search during the diagnostic phase.
1. Damaged Wiring or Connectors
The wiring harness on the F150 sits in a high-heat environment. Over time, the plastic connectors for the ignition coils can become brittle and crack. A loose locking tab can allow the connector to vibrate just enough to break the electrical connection, triggering the code intermittently.
2. Failed Ignition Coil (COP)
Internal shorts within the ignition coil are common. As the internal copper windings degrade, the resistance changes. If the resistance falls outside of the factory specifications, the PCM will immediately flag the circuit as faulty. Heat and vibration are the primary enemies here.
3. PCM Driver Failure
This is the “worst-case” scenario but it does happen on older models. The transistor inside the PCM that handles the grounding of the coil circuit can burn out. This usually happens if a shorted coil is left unrepaired for too long, essentially “back-feeding” high voltage into the computer.
Step-by-Step Diagnostic Guide for the p0355 ford f150
Before you start pulling parts, gather your tools. You will need a basic OBD2 scanner, a digital multimeter, and a 7mm or 8mm socket (depending on your engine year). Safety is paramount, so ensure the engine is cool to the touch before reaching near the fuel rails or manifold.
Step 1: The Visual Inspection
Pop the hood and locate cylinder 5 on the front of the driver’s side. Inspect the connector for any signs of corrosion or melting. Look closely at the wires leading into the connector; it is common for rodents to chew on the soy-based wiring insulation found in many modern Fords.
Tug gently on the wires to ensure they are securely pinned into the plastic housing. If the locking tab on the connector is broken, the connector may have backed off. This is a very common “easy fix” that many people overlook before buying expensive parts.
Step 2: The Coil Swap Test
This is the most effective way to confirm if the coil itself is dead. Swap the ignition coil from cylinder 5 with the one from cylinder 6 (right next to it). Clear the codes with your scanner and start the engine. If the code changes from P0355 to P0356, you have confirmed the coil is the culprit.
However, if the P0355 code returns despite the swap, the problem is definitely in the wiring harness or the PCM. This simple test saves you from buying a new coil only to find out the wire was pinched or broken further up the loom.
Step 3: Multimeter Testing
Set your multimeter to DC volts. With the ignition on but the engine off, unplug the connector for coil 5. Test the power wire (usually the red or light-colored wire) against a known good ground. You should see battery voltage (approximately 12.6V).
Next, you need to check the trigger wire. This is more difficult as it requires a pulse, but you can check for continuity from the coil connector back to the PCM pin. If you find “infinite resistance” (OL) on your meter, there is a break in the wire that needs to be spliced and repaired.
Required Tools and Materials for Repair
If you have confirmed a part failure, having the right supplies on hand will make the job go smoothly. I always recommend using OEM Motorcraft parts for ignition components. Fords are notoriously picky about aftermarket coils, which often have different resistance levels that can trigger “ghost” codes.
- Replacement Ignition Coil: Specifically for the Ford 5.0L, 3.5L, or 5.4L engine.
- Dielectric Grease: Apply a small amount to the inside of the coil boot to prevent moisture intrusion and arcing.
- Contact Cleaner: Use this to spray out any oil or debris from the harness connector.
- Heat Shrink Tubing: If you find a broken wire, use heat shrink rather than electrical tape for a permanent, weather-proof seal.
Using a small amount of anti-seize on the spark plug threads (if you choose to replace them while you are in there) is also a good practice. Just be careful not to get any on the electrodes, as this can cause a different type of misfire.
How to Replace the Ignition Coil Safely
Replacing the coil is a straightforward task, but there are a few “pro tips” that can prevent future issues. First, always disconnect the negative battery terminal when working on electrical circuits. This prevents accidental shorts that could damage the sensitive PCM drivers.
- Remove the 7mm or 8mm bolt holding the coil to the intake manifold.
- Gently twist and pull the coil upward to break the seal of the rubber boot on the spark plug.
- Inspect the spark plug hole for any oil or coolant. If oil is present, your valve cover gasket may be leaking, which can kill new coils quickly.
- Apply dielectric grease to the new coil boot and press it firmly onto the spark plug.
- Reinstall the mounting bolt—do not over-tighten it, as the brass inserts in the plastic manifold can strip easily.
Once the new coil is in place and the connector is clicked home, reconnect the battery. Start the truck and let it idle for a few minutes. The p0355 ford f150 code should stay away, and the idle should smooth out almost immediately.
Frequently Asked Questions About p0355 ford f150
Can I drive my F150 with a P0355 code?
It is not recommended. Driving with a dead ignition circuit allows raw fuel to enter the exhaust stream. This fuel will ignite inside the catalytic converter, potentially melting the internal honeycomb structure and leading to a repair bill in the thousands.
Why does my P0355 code only happen when it rains?
This usually indicates a crack in the ignition coil housing or a compromised wiring harness. Moisture enters the crack and provides an easier path for electricity to reach the ground than the spark plug. Replacing the coil and checking the weather seals on the connectors usually solves this.
Is it necessary to replace all coils at once?
While not strictly necessary, if your truck has over 100,000 miles, the other coils are likely near the end of their lifespan. Many DIYers choose to replace all of them to ensure consistent performance and avoid doing the same job again in two weeks for a different cylinder.
Does a P0355 mean my computer is blown?
Not necessarily. While a failed PCM driver is a possibility, it is the least common cause. Exhaust all wiring and coil tests first. Only consider the PCM if you have confirmed 12V power at the coil but no ground pulse coming from the computer during cranking.
Final Thoughts on Resolving Your Ignition Issues
Taking care of a p0355 ford f150 fault is a manageable task for any weekend mechanic with a bit of patience. By following a logical diagnostic path—checking the connector, swapping the coil, and verifying the wiring—you can avoid the “parts cannon” approach and fix the truck correctly the first time.
Remember that your Ford is a precision machine. Using high-quality components and ensuring clean electrical connections will keep your truck on the trails and off the tow truck. If you ever feel overwhelmed by the electrical testing, do not hesitate to consult a certified technician who has an oscilloscope to see the circuit pulses in real-time.
Keep your tools clean, stay patient with those plastic clips, and you will have that V8 or EcoBoost purring again in no time. Stay safe and keep your truck ready for the next adventure!
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