P0355 — Ignition Coil « E » Primary/Secondary Circuit
**Overview**
The diagnostic trouble code **P0355** indicates a problem specifically related to the primary or secondary circuit of the **fifth ignition coil (« E »)** in your vehicle’s ignition system. In simple terms, this means that the vehicle’s engine control unit (ECU) has detected an abnormality or malfunction in the electrical circuit that powers the fifth ignition coil, which is responsible for firing one of the engine’s spark plugs.
It is important to note that **labels for this code may vary between vehicle manufacturers**; some may use different code numbers or naming conventions for similar issues involving ignition coils.
**Fast Facts**
– System affected: Ignition system / Cylinder ignition coil circuit
– Severity: Moderate — depending on the underlying cause, but it can impact engine performance
– Main symptoms: Engine misfire, rough running, poor acceleration
– Driveability: Limited — vehicle may idle roughly or have trouble accelerating, but it can often be driven for short distances
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**Manufacturer variations for trouble code P0355**
Different vehicle manufacturers may label or code this issue differently, which can sometimes lead to confusion during diagnosis. Common variations include:
– **Honda / Acura:** P0355 (sometimes accompanied by manufacturer-specific descriptions)
– **Ford:** P0355
– **Volkswagen / Audi:** P0355
– **BMW / Mini:** P0355
– **Toyota / Lexus:** P0355 or sometimes a different but similar code within their systems
It is essential to cross-reference the specific vehicle’s repair manual or OBD-II code list to confirm the exact label and meaning for each manufacturer.
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**What does trouble code P0355 mean?**
The **P0355** code signifies that the ECU has detected an electrical issue in the **primary circuit of ignition coil « E »**. The ECU constantly monitors the ignition coils for proper operation by reading signals from the coil’s **integrated ignition module** or **ignition control module**.
When the ECU detects discrepancies such as **high resistance, open circuits, short circuits, or faulty signals** in the coil’s wiring or control circuit, it sets this DTC (Diagnostic Trouble Code). This typically occurs during engine operation when the ECU notices a **misfire or abnormal current flow** in the coil circuit.
Usually, the problem appears when the ignition coil « E » fails to respond correctly or there is an interruption in the electrical signal that controls it, leading to misfiring in the associated cylinder.
**In simple terms:**
Imagine the ignition coil as an electrical switch that fires the spark plug when needed. If the switch gets stuck or doesn’t turn on at the right time, the spark doesn’t ignite the fuel mixture properly. The ECU detects this as an electrical issue in that coil’s circuit and flags it as trouble code P0355.
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**Severity and risks of trouble code P0355**
The significance of **P0355** depends largely on the root cause and the engine’s condition. Generally, this code indicates a **moderate issue** that can lead to **performance problems** if not addressed. Common risks include:
– **Engine misfire**, which can cause rough idling and hesitation
– **Reduced fuel efficiency**, due to incomplete combustion
– **Potential damage to other engine components**, such as spark plugs or catalytic converters, if misfire persists
– **Increased emissions**, resulting in environmental impact and potential failed emissions tests
**Can the vehicle be driven?**
In most cases, the vehicle can be driven **limitedly**—but caution is advised. Prolonged driving with this issue can lead to more severe damage or loss of power. It is best to repair the problem promptly.
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**Symptoms of trouble code P0355**
When this code is active, you may notice some or all of the following symptoms:
– **Engine misfire**, especially under load or acceleration
– **Rough or uneven idle**
– **Loss of power** or reduced acceleration ability
– **Engine hesitation or stalling** at low speeds
– **Check Engine Light (CEL or MIL)** illuminated on the dashboard
– **Poor fuel economy**
– Potential **subtle vibrations or shaking** during engine operation
Many of these symptoms can be mistaken for other engine problems, so it’s crucial to perform proper diagnostics.
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**Most likely causes of trouble code P0355**
This trouble code generally arises from electrical or mechanical issues affecting the fifth ignition coil circuit. The most common causes include:
1. **Faulty ignition coil « E »** – an actual defective coil, which can cause misfiring in its cylinder.
2. **Damaged or corroded wiring or connector** – corrosion, broken wires, or loose connections in the wiring harness leading to the coil.
3. **Open or shorted wiring circuit** – interrupted or damaged wiring can prevent proper electrical flow.
4. **Faulty ignition coil control module or ECU** – if the control module or ECU doesn’t send correct signals, misfires will occur.
5. **Incorrect or contaminated spark plug** – although less common, a worn spark plug might contribute to misfire symptoms related to the coil.
Generally, **the most common cause is a failure of the coil or its wiring**, followed by control circuit issues.
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**How to diagnose trouble code P0355**
Diagnosing P0355 involves a systematic approach to identify the root cause accurately and safely:
1. **Visual Inspection**
Examine the coil « E » and its wiring harness for signs of damage, corrosion, or looseness. Check the connector for corrosion or debris.
2. **Check for other codes**
Use an OBD-II scanner to verify if other related codes are present, such as misfire codes or wiring faults.
3. **Live data monitoring**
Using a diagnostic tool, observe the ignition coil’s control signals and secondary ignition voltages while the engine is running. Unusual readings can pinpoint failures.
4. **Inspect wiring continuity**
Test the wiring harness from the ECU to the coil for continuity, ensuring no open or short circuits. Use a multimeter set to measure resistance or continuity.
5. **Test the ignition coil « E »**
Swap the coil with another cylinder’s coil (if possible) to see if the problem moves. If the code or symptoms follow the coil, it indicates a faulty coil.
6. **Perform a coil resistance test**
Measure primary and secondary coil resistances against manufacturer specifications.
7. **Check the control module and ECU**
If wiring and coil are OK, assess whether the control signals sent by the ECU are correct. This may require manufacturer-specific tools or experience.
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**Possible repairs for trouble code P0355**
Based on the diagnosis, repairs will vary. Common fixes include:
– **Replacing the ignition coil « E »** — usually a straightforward repair, can be performed by a professional or a skilled DIYer.
– **Repairing or replacing damaged wiring or connectors** — involves cleaning, re-soldering, or replacing faulty wires. This is a basic repair but best performed by a professional if extensive wiring is involved.
– **Clearing corrosion or contamination** — cleaning contacts with electrical contact cleaner.
– **Replacing the ignition coil control module or ECU** — more complex and often requires professional diagnosis and programming.
– **Replacing spark plugs** if they are worn or contaminated, to prevent ignition problems.
Keep in mind that each repair should follow manufacturer recommendations and safety protocols.
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**Vehicles commonly associated with trouble code P0355 in Europe**
In Europe, various vehicle brands have reported P0355 in service records, especially those with flexible ignition systems. Common vehicle groups include:
– **Volkswagen Group** (Volkswagen, Audi, Škoda, SEAT)
– **Ford** (various models with coil-on-plug systems)
– **BMW / Mini**
– **Peugeot / Citroën**
– **Toyota / Lexus**
The exact engine family and models vary depending on the vehicle’s year and configuration, so always consult manufacturer-specific diagnostic data.
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**Frequent mistakes & best practices**
When diagnosing or repairing P0355, common errors include:
– **Misinterpreting the code without checking wiring integrity** — wiring issues are often overlooked.
– **Assuming coil failure without testing** — always verify coil resistance and swap test first.
– **Not inspecting connectors properly** — corrosion or debris can cause intermittent faults.
– **Ignoring other related codes** — secondary misfire or circuit codes often indicate broader issues.
– **Replacing parts without proper testing** — costly repairs can be avoided with thorough diagnostics.
To avoid these errors, always follow systematic testing procedures and refer to manufacturer specifications.
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**FAQ — trouble code P0355**
**Can this code disappear on its own?**
It is unlikely that P0355 will resolve spontaneously. Electrical faults like corroded connectors or broken wires generally persist until repaired.
**Can I keep driving?**
Limited driving is possible, but it’s not advisable to ignore the problem. Prolonged driving can cause further damage and worsen fuel economy or emissions.
**Why does the code return after clearing it?**
If the underlying issue is not fixed—such as a faulty coil, wiring problem, or control circuit—the code will likely come back once the ECU re-detects the problem during engine operation.
**Is it safe to drive with this code?**
While not immediately dangerous, driving with this fault could lead to engine misfire, increased emissions, and possible damage to other components. It’s best to seek diagnosis and repair promptly.
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This diagnostic sheet aims to guide you through understanding, identifying, and addressing P0355 efficiently and systematically. Always follow safety procedures and manufacturer guidelines for the most accurate and reliable repairs.