P0355 on 2002-2006 Chevrolet Avalanche 8.1L: Ignition Coil 'E' Circuit Causes and Fixes

What's Unique About the 2002-2006 Chevrolet Avalanche

The 2002-2006 Avalanche 2500 uses the 8.1L Vortec V8 (RPO code L18), a large displacement big-block engine, which is less common than the 5.3L small-block found in the 1500 models. It uses a robust coil-near-plug ignition system with eight individual coils, each connected to its spark plug via a short wire. While individual coil failure is common, these GMT800 platform trucks are also known for having potential issues with main PCM ground wires, which can cause a variety of difficult-to-diagnose electrical and sensor codes, including ignition circuit faults. A well-documented issue involves the ground straps located at the back of the cylinder heads; 🎬 Watch: How to find and fix bad Chevy truck ground wires if they become corroded or broken, intermittent and bizarre electrical behavior can result. An iATN post noted a 2004 Avalanche 8.1L that threw codes for six ignition coils simultaneously, pointing towards a shared electrical issue like a ground fault rather than six failed coils. The crankshaft position sensor is also a very common failure point on the 8.1L, which can cause stalling and no-start conditions that might be confused with an ignition system failure.

Symptoms You May Notice

• Check Engine Light is on
• Engine shaking, stumbling, or vibrating (misfire)
• Rough idle
• Noticeable loss of engine power, especially under load
• Engine may hesitate or stall
• Possible smell of raw fuel from the exhaust
• Flashing Check Engine Light if the misfire is severe enough to threaten the catalytic converters
🎬 See this video on diagnosing an 8.1L Silverado engine misfire

Most Likely Causes

1. Failed Ignition Coil on Cylinder #5 🔴 High Probability → Shop Ignition Coil Ignition coils are a common wear item that fail from age, heat cycles, and vibration. The 8.1L is known for running hot, especially in a heavy-duty application, which contributes to faster wear. There is no specific design flaw, but they are the most frequent point of failure for this code.
   How to confirm: Locate cylinder #5 (driver's side, third from the front). Swap the ignition coil from cylinder #5 with the coil from another cylinder (e.g., cylinder #3, driver's side, second from front). Clear the codes and drive the vehicle. If the code changes to P0353 (for cylinder #3), the ignition coil is confirmed to be faulty. This is the definitive DIY test.
   Typical fix: Replace the failed ignition coil. Many owners choose to replace all eight coils at once as a preventative measure, especially on a high-mileage engine, as the others are likely of the same age and condition.
   Est. part cost: $40-$75 for a single OEM-quality coil.
2. Worn Spark Plug or Faulty Spark Plug Wire 🟡 Medium Probability → Shop Spark Plug The 8.1L Vortec is notoriously hard on spark plugs, partly due to its tendency to consume oil. Oil fouling can cause plugs to fail prematurely, with replacement often needed as frequently as every 25,000 miles. A plug with an excessive gap or a wire with high resistance can overwork the ignition coil, leading to its failure or causing a circuit fault code on its own.
   How to confirm: After confirming the coil is good, remove the spark plug and wire for cylinder #5. Inspect the spark plug for wear, heavy carbon or oil fouling, or cracks in the ceramic insulator. Inspect the wire for corrosion on the terminals, physical damage, or brittleness. Test the wire's resistance with a multimeter; it should be within the manufacturer's specification (typically under 1,000 ohms per foot).
   Typical fix: Replace the spark plug and/or spark plug wire. It is best practice to replace all spark plugs and wires as a set, especially given the 8.1L's reputation for plug wear.
   Est. part cost: $5-$15 for a single spark plug, $50-$100 for a full set of wires.
3. Wiring Harness or Connector Issue ⚪ Low Probability The engine bay environment is harsh. Wires can become brittle and break, or the plastic connector for the ignition coil can become damaged. On GMT800 trucks, poor PCM ground connections at the back of the engine block are a known issue that can cause random electrical faults. A broken ground wire can cause multiple ignition coil codes at once.
   How to confirm: Visually inspect the wiring harness and connector going to the cylinder #5 ignition coil. Look for any signs of chafing, melting, or corrosion on the pins. Check the main engine-to-chassis and PCM ground straps for tightness and corrosion. These are typically located on the back of the cylinder heads. Use a multimeter to check for 12V power (Pink wire) and a proper ground signal at the coil connector with the key on.
   Typical fix: Repair the broken or corroded wire. Replace the pigtail connector if it's damaged. Clean and tighten any loose or corroded ground connections. In one documented case, a user on GM-Trucks.com found a broken wire in the main harness that was causing an intermittent misfire on cylinder 5.
   Est. part cost: $10-$25 for a new pigtail connector.

Rare But Worth Checking

• Faulty Powertrain Control Module (PCM): → Shop Engine Control Module (ECM) This is the least likely cause. The internal driver circuit for the #5 coil can fail inside the PCM. This should only be considered after all other possibilities (coil, plug, wire, and all wiring) have been exhaustively tested and ruled out. Before condemning the PCM, it is critical to verify all power and ground circuits to the module itself.
• Shorted 5V Reference Circuit: On some GM trucks, the Crankshaft Position Sensor (CKP) can share a 5V reference circuit with other components. A short in this circuit can cause a variety of codes, including false ignition system codes, and may put the vehicle into 'reduced power' mode. While not a direct cause of P0355, it can create a complex electrical scenario that includes ignition-related symptoms.

Diagnosis Steps

1. Read the code with an OBD-II scanner to confirm P0355 and check for any other codes like P0305.
2. Locate cylinder #5. On the 8.1L V8, cylinders are numbered 1-3-5-7 on the driver's side (front to back) and 2-4-6-8 on the passenger's side. Cylinder #5 is the third cylinder back from the front on the driver's side.
3. Inspect the ignition coil, spark plug wire, and the area around them for any obvious damage, looseness, or fluid leaks.
4. The Coil Swap Test: Swap the ignition coil from cylinder #5 with an easily accessible one, like cylinder #1 or #3. Clear the codes, start the engine, and let it run for a minute. Re-scan for codes. If the code has moved to the cylinder you swapped with (e.g., P0351 or P0353), the coil is bad and needs to be replaced. This is the most effective first step.
5. If the code stays P0355: The problem is not the coil. Proceed to inspect the spark plug wire and spark plug for cylinder #5. Given the 8.1L's tendency to foul plugs, pull the plug and inspect it for oil or carbon buildup. Replace them if they are worn or damaged.
6. If the plug and wire are good: The issue is likely in the wiring. Disconnect the coil connector for cylinder #5. With the ignition key in the 'ON' position, use a multimeter to check for 12-volt power on the pink wire. Check the black wire for a good ground. The third wire is the trigger signal from the PCM.
7. Inspect the main PCM ground wires. On GMT800 trucks, these are notoriously located at the rear of the cylinder heads, near the firewall. They are difficult to see but are a common source of strange electrical issues. Ensure they are clean, tight, and not broken.
8. If all wiring, grounds, the coil, plug, and wire are confirmed to be good, the fault may lie within the PCM itself, which may require professional diagnosis.

Parts You'll Likely Need

• Ignition Coil (OEM #12558693) — This is the most common component to fail and cause a P0355 code. This is a square-style coil made by Mitsubishi for GM.
  Trusted brands: ACDelco (GM Genuine), NGK, Delphi, Standard Motor Products
  OEM price range: $40-$75
  Aftermarket price range: $25-$50
• Spark Plugs (Set of 8) (OEM #12571164 (ACDelco 41-983)) — The 8.1L is known to be hard on spark plugs due to heat and potential oil consumption, making them a frequent maintenance item.
  Trusted brands: ACDelco Iridium, NGK Iridium IX
  OEM price range: $8-$12 per plug
  Aftermarket price range: $6-$10 per plug
• Ignition Coil Connector Pigtail (OEM #PT2135 (ACDelco)) — The plastic connector and its locking tab can become brittle from engine heat and break during service. The terminals can also corrode or lose their tension, causing a poor connection.
  Trusted brands: ACDelco, Standard Motor Products, Dorman
  OEM price range: $20-$35
  Aftermarket price range: $10-$20

Related Codes That Often Appear With This One

• P0305 — P0305 means 'Cylinder 5 Misfire Detected'. Since P0355 indicates a fault in the ignition circuit for cylinder 5, a misfire on that same cylinder is the direct result. These codes almost always appear together.

Technical Service Bulletins (TSBs) & Recalls

• While no TSB is directly for P0355, TSB 02-06-01-035 was issued for excessive oil consumption on 8.1L engines, a condition that leads to premature spark plug fouling and can contribute to ignition system faults. The fix involved replacing intake manifold bolts and later, updated intake gaskets (P/N 89017539 for early 2001-2004 engines).
• Manufacturer service bulletin #PIP5038B notes that a technician may find P0355 along with other ignition coil and misfire codes (P0300-P0306 and P0351-P0356) and should follow published service information diagnostics.
• Manufacturer service bulletin #PIT5677E and #PIT5677 describe scenarios where P0355 may be found in combination with a wide variety of other electrical system DTCs, such as P0340, P0341, and P0365.

Platform-Specific Known Issues

• A user on GM-Trucks.com chased a P0305 (Cylinder 5 Misfire) for an extended period. After replacing the coil, plug, wire, and injector, the problem was finally traced to a broken lifter. While P0355 is an electrical code, a severe underlying mechanical issue could potentially cause confusing symptoms, though it's not a direct cause. The user noted a 'gravelly sound' from the rocker arms on that cylinder when listening with a stethoscope.

Mechanic-Grade Diagnostic Values

• Ignition Coil Primary Resistance — expected: 0.6 - 1.0 ohms. Failure: A reading of OL (Open Loop) or significantly outside this range indicates a faulty coil.
• Ignition Coil Secondary Resistance — expected: 5.0k - 11.0k ohms. Failure: A reading of OL (Open Loop) or significantly outside this range indicates a faulty coil.
• Ignition Coil Connector - Power Supply — expected: 12V+ (battery voltage) on the Pink wire with Key On, Engine Off.. Failure: Low or no voltage indicates a problem with the ignition power feed, fuse, or relay.
• Ignition Coil Connector - Ground — expected: Good ground continuity on the Black wire.. Failure: High resistance to ground points to a bad ground connection, likely at the cylinder head or engine block.

Scan Tool Commands That Help

• Tech2 / GDS2: Cylinder Power Balance Test — This function allows a technician to sequentially disable injectors on each cylinder to determine which cylinder is not contributing to engine power. While P0355 already points to cylinder 5, this test can confirm the severity of the miss and ensure no other cylinders are weak.
• Tech2 / GDS2: Misfire Graphic — Provides a real-time count of misfire events per cylinder. This is useful for confirming the misfire is isolated to cylinder #5 and does not migrate or appear randomly on other cylinders, which would suggest a different root cause (like a fuel or vacuum issue).

Wiring & Ground Locations

• G104 (for 8.1L) — On the rear of the left (driver's side) cylinder head.. This is a primary ground point for the engine harness. A loose or corroded connection here can cause intermittent and difficult-to-diagnose electrical faults for multiple sensors and actuators, including the ignition coils. It is a known trouble spot on GMT800 trucks.
• G103 (Gas Engines) — On the left rear of the engine block.. Another critical engine ground. While G104 is more specific to the cylinder head components, G103 provides a main ground path for the engine block. Both should be checked for integrity.
• Ignition Coil Connector — Plugged into the ignition coil for cylinder #5.. This connector has four pins: Pink (Ignition Voltage), Black (Ground), Dark Green/White (IC Timing Control from PCM), and Light Green (IC Timing Control Feedback). A test light or scope on the Dark Green/White wire should show a signal pulse when cranking. The PCM sets P0355 when it doesn't see the expected activity on this circuit.
• PCM Connector C2 (Green) — At the Powertrain Control Module (PCM), typically on the driver's side fender well.. Pin 34 (Dark Green/White wire) on the C2 connector is the Ignition Control (IC) signal for coil #5. If all wiring at the coil is good, a continuity test from this pin to the coil connector can confirm the wire is intact. A fault here points directly to the PCM driver.

Real Owner Repair Stories

• GM-Trucks.com forum user (2002 Chevrolet Silverado 2500HD 8.1L) — Intermittent P0355 and P0305 codes, rough running, especially when the engine was hot.
  ❌ Tried (didn't work) Replaced ignition coil on cylinder #5, Replaced spark plug and wire on cylinder #5, Swapped coil with another cylinder (code did not follow)
  ✅ What actually fixed it The user found a broken wire for the cylinder #5 coil inside the main wiring harness loom where it ran over the driver's side valve cover. The insulation was intact, but the copper wire inside was broken, causing an intermittent connection that worsened with engine heat and vibration. Splicing the wire and securing the harness fixed the issue permanently.

OEM Part Supersession History

• 12558693 → 19418993 — Standard part number update and consolidation by GM.
  Heads up: The original coils were made by Mitsubishi for GM. The D585 coil style is often discussed as a replacement, but it's crucial to get genuine ACDelco or Delphi parts, as many forum users report premature failure with no-name aftermarket brands. The physical coil is a square shape with a heat sink.

Model Year Variations Within This Range

• 2004-2006: Starting in 2004, the 8.1L L18 engine switched from a return-style fuel system to a returnless system. This does not directly affect the P0355 code diagnosis but is a significant change in the overall engine management system for these years.
• 2003+: In 2003, the engine received a new Powertrain Control Module (PCM), designated P59, which had a faster processor and more memory. This may affect scan tool communication protocols and diagnostic capabilities compared to the 2002 models.
• 2006: The Avalanche 2500 with the 8.1L engine was discontinued after the 2005 model year, so it is not present in the 2006 lineup.

Diagnostic Flowchart

Other Known Issues on This Vehicle

Issues unrelated to this code that are worth knowing about as an owner of this generation:

• Excessive Oil Consumption 🔴 High — Extremely common across the entire 8.1L engine line. Many owners report using a quart of oil every 1,000-3,000 miles. The issue is often linked to the PCV system design pulling oil vapor through the intake manifold. (Ref: TSB 02-06-01-035)
• Crankshaft Position Sensor (CKP) Failure 🔴 High — Considered one of the most common and frustrating failure points on the 8.1L Vortec. Failure is often heat-related and can cause intermittent stalling, a no-start condition when hot, or rough idling.
• Hydroboost Brake System Leaks/Failure 🟠 Medium — The power-steering-assisted hydroboost unit is prone to leaking, often internally into the cabin at the firewall. Failure can also cause a hard brake pedal or whining from the power steering pump.
• Intake Manifold Gasket Leaks 🟠 Medium — Common to many Vortec engines, the 8.1L can suffer from failed intake manifold gaskets, leading to vacuum leaks (rough idle, poor performance) or coolant leaks. (Ref: Related to TSB 02-06-01-035 for oil consumption.)
• Frequent Spark Plug Fouling 🟡 Low → Shop Spark Plug — A direct consequence of the oil consumption issue. Plugs often need to be replaced far more frequently than on other engines, sometimes as often as every 25,000 miles, to prevent misfires.

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: A used OEM ignition coil from a low-mileage donor vehicle can be a cost-effective and reliable option, as genuine ACDelco/Delphi coils are known to be more durable than many cheap aftermarket alternatives. Given that the coil is the most likely failure point, sourcing a single used OEM coil to confirm the diagnosis before buying a new one is a smart strategy.

Donor-vehicle mileage cap: roughly under 100000 miles for the part to have meaningful remaining life.

What to inspect on the donor part:

• Check for cracks in the epoxy casing.
• Inspect the electrical connector for corrosion or damage.
• Look for the original manufacturer stampings (e.g., Mitsubishi or Delphi markings).
• Avoid coils with significant rust on the metal heat sink/bracket.

OEM-only on this vehicle (don't cheap out):

• Powertrain Control Module (PCM) - Aftermarket or improperly programmed PCMs can cause a host of issues. A replacement should be from a reputable rebuilder or a new OEM unit programmed specifically to the vehicle's VIN.

Aftermarket brands forum-validated for this vehicle:

• ACDelco (GM Genuine)
• Delphi
• NGK (for coils and plugs)
• Standard Motor Products (often considered a reliable Tier 1 supplier)

Brands owners have reported issues with on this vehicle:

• Unbranded, 'no-name' ignition coils sold in bulk sets on marketplaces like eBay or Amazon. Forum users consistently report high rates of premature failure with these parts.

Real Owner Stories

Aggregated from forums and TSBs cited above. Mileages and costs reflect what owners reported in those sources.

Related OBD-II Codes

• P0305 — This is the specific cylinder 5 misfire code that often accompanies P0355 when the ignition circuit failure prevents the cylinder from firing.
• P0353 — The ignition coil circuit code for cylinder #3; it is mentioned as the code that would appear if you swapped a faulty cylinder #5 coil to the #3 position during diagnosis.
• P0351 — The ignition coil circuit code for cylinder #1; another companion code used during the coil swap diagnostic procedure.
• P0300 — A random/multiple cylinder misfire code that may trigger if ground wire issues at the back of the cylinder heads affect multiple coils simultaneously.

Frequently Asked Questions