P0305 on 2010-2012 GMC Canyon: Cylinder 5 Misfire Causes and Fixes

What's Unique About the 2010-2012 Gmc CANYON

The 2010-2012 GMC Canyon offered both a 3.7L inline-5 and a 5.3L V8, both of which can register a P0305 code. The 3.7L I5 uses a coil-on-plug ignition system, where failures are almost always the coil or plug itself. However, the Atlas engine family (which includes the 3.7L) is also known for premature valve seat wear, which can cause a persistent P0305 that is not resolved by ignition or fuel parts. The 5.3L V8 uses a coil-near-plug system with short spark plug wires. GM issued a Technical Service Bulletin (PIP4819A) specifically mentioning that loose spark plug wires can cause misfires on these engines, making it a critical and vehicle-specific first check for V8 owners.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this vehicle.

Symptoms You May Notice

• Rough or shaking idle
• Hesitation or stumbling during acceleration
• Noticeable loss of engine power
• Flashing or solid Check Engine Light
• Poor fuel economy
• Potential fuel odor from the exhaust
• Sensation of driving over a bump strip during acceleration

Most Likely Causes

1. Faulty Ignition Coil 🔴 High Probability Ignition coils on the GM Atlas engine family (which includes the 3.7L I5) are a very common failure item leading to misfires. The 5.3L V8 coils are also common failure points.
   How to confirm: Swap the ignition coil from cylinder 5 with a coil from another cylinder (e.g., cylinder 1). Clear the codes and drive. If the code changes to P0301, the coil is bad. The coil is held on by a single 10mm bolt.
   Typical fix: Replace the faulty ignition coil. It is held in by a single 10mm bolt. 🎬 See how to replace the ignition coil and spark plugs
   Est. part cost: $30-$70
2. Worn or Fouled Spark Plug 🔴 High Probability
   How to confirm: Remove the spark plug from cylinder 5 and inspect it for wear, carbon buildup, or oil/fuel fouling. You can also swap it with another cylinder's plug to see if the misfire code follows. Check the gap; it should be between 0.024 and 0.071 inches.
   Typical fix: Replace the spark plug. It is best practice to replace all spark plugs at the same time for even performance. Always use the OEM recommended Iridium plugs.
   Est. part cost: $10-$25 per plug
3. Loose or Faulty Spark Plug Wire (5.3L V8 Only) 🟡 Medium Probability A GM Technical Service Bulletin (PIP4819A) specifically calls out loose spark plug wires as a cause for misfires on this platform. Owners report that aftermarket wires can sometimes be too long and rub against the steering shaft, causing damage or pulling the wire loose.
   How to confirm: Visually inspect the spark plug wire for cylinder 5. Ensure it is securely clicked onto both the ignition coil and the spark plug. Check for any signs of damage, corrosion, or chafing against other components like the steering shaft.
   Typical fix: Reseat or replace the spark plug wire. It is recommended to replace them as a full set. Ensure the new wire is properly routed away from moving parts.
   Est. part cost: $50-$90 for a set
4. Clogged or Failing Fuel Injector ⚪ Low Probability
   How to confirm: This is more difficult to diagnose. A professional can perform a fuel injector balance test. A DIY method involves swapping the injector with another cylinder, but this is labor-intensive and may require removing the intake manifold on the 3.7L I5.
   Typical fix: Replace the faulty fuel injector. It is often recommended to replace all injectors as a set due to the labor involved.
   Est. part cost: $60-$150

Rare But Worth Checking

• Low Engine Compression (Worn Valve Seats): For the 3.7L I5 engine, a persistent P0305 that isn't fixed by ignition or fuel parts is often caused by a worn intake valve seat in the cylinder head. This was a known issue on the Atlas engine family, particularly on earlier models, but can still occur on 2010-2012 trucks. A compression or cylinder leak-down test is required to confirm this.
• Vacuum Leak: A leak in a vacuum hose or intake manifold gasket near cylinder 5 can lean out the air/fuel mixture and cause a misfire.
• Engine Wiring Harness Chafing: Several GM TSBs for related trucks (e.g., PIP5416) mention that the engine wiring harness can chafe against various components like the A/C compressor or brackets, causing shorts that can lead to misfires and other electrical issues. While not specific to P0305 on the Canyon, it is a plausible cause if other diagnostics fail.

Diagnosis Steps

1. Confirm the code with an OBD-II scanner. 🎬 Watch this simple explanation of the P0305 misfire code Note if the check engine light is flashing, which indicates a severe misfire that can damage the catalytic converter.
2. Identify your engine (3.7L I5 or 5.3L V8) to follow the correct procedure.
3. Locate cylinder 5. On the 3.7L I5, it is the rearmost cylinder, closest to the firewall. On the 5.3L V8, it is the third cylinder back on the driver's side.
4. For 5.3L V8 only: Inspect the spark plug wire for cylinder 5. Ensure it is fully seated at both the coil and the plug. Check for damage or chafing. This is a known issue per TSB PIP4819A.
5. Swap the ignition coil from cylinder 5 with the coil from cylinder 1. This requires a 10mm socket. Clear the codes and run the engine. If the code returns as P0301, the ignition coil is faulty and needs replacement.
6. If the code remains P0305, remove the spark plug from cylinder 5. Inspect it for wear, damage, or fouling. Replace if necessary. It's best to replace all plugs at once.
7. If the coil and plug are good, the next most likely cause is a faulty fuel injector. This may require professional diagnosis or a more involved DIY swap.
8. For 3.7L I5 only: If ignition and fuel components are confirmed good, perform a compression test on cylinder 5. Low compression (below 100 PSI) strongly suggests a mechanical engine problem, most likely a worn valve seat, which is a known issue on this engine.

Parts You'll Likely Need

• Ignition Coil (I5) (OEM #ACDelco D1935E (GM 19300921)) — This is one of the most common failure points for a single-cylinder misfire on the 3.7L I5 engine.
  Trusted brands: ACDelco, Delphi, NGK
  OEM price range: $50-$80
  Aftermarket price range: $30-$60
• Ignition Coil (V8) (OEM #ACDelco D585 (GM 10457730)) — The 'D585' or 'truck coil' is a very common replacement part for misfires on the 5.3L V8.
  Trusted brands: ACDelco, Delphi, MSD
  OEM price range: $40-$60
  Aftermarket price range: $25-$50
• Iridium Spark Plug (I5) (OEM #ACDelco 41-103) — Spark plugs are a regular maintenance item and a frequent cause of misfires as they wear out.
  Trusted brands: ACDelco, NGK, Bosch
  OEM price range: $15-$25
  Aftermarket price range: $10-$20
• Iridium Spark Plug (V8) (OEM #ACDelco 41-985 (superseded by 41-110)) — Worn spark plugs are a common cause of misfires. The original 41-985 has been updated by GM.
  Trusted brands: ACDelco, NGK
  OEM price range: $12-$20
  Aftermarket price range: $8-$15
• Spark Plug Wire Set (5.3L V8 Only) (OEM #ACDelco 9748RR) — A GM TSB points to loose or faulty wires as a specific cause of misfires on these V8 engines.
  Trusted brands: ACDelco, Delphi, NGK
  OEM price range: $70-$100
  Aftermarket price range: $50-$80

Related Codes That Often Appear With This One

• P0300 — If the misfire becomes more frequent or other cylinders begin to misfire, a P0300 (Random/Multiple Cylinder Misfire) may appear alongside P0305.
• P0420 — If a misfire is left unaddressed, it can dump unburnt fuel into the exhaust, damaging the catalytic converter and eventually triggering a P0420 (Catalyst System Efficiency Below Threshold) code.

Technical Service Bulletins (TSBs) & Recalls

• PIP4819A

Platform-Specific Known Issues

• TSB PIP4819A: For the 5.3L V8 engine, GM issued a bulletin stating that misfire codes (including P0305) can be caused by loose spark plug wires. The fix is to inspect and replace any wires that are not secure.
• Known Valve Seat Issue (3.7L I5): The Atlas engine family has a well-documented history of premature intake valve seat wear, leading to loss of compression and misfires. TSB PIP4013C (and its later revisions) addresses diagnosing misfires at idle caused by this. If ignition and fuel system checks don't solve P0305, a compression test is mandatory.

Mechanic-Grade Diagnostic Values

• Fuel Pressure (Key On, Engine Off) — expected: 55-62 PSI. Failure: Pressure below 55 PSI suggests a weak fuel pump or a leak.
• Fuel Injector Resistance (3.7L I5) — expected: ~12.6 Ohms. Failure: A reading that is significantly different (more than 0.5 ohms) from other injectors, or an open circuit.
• Fuel Injector Resistance (5.3L V8) — expected: 11-14 Ohms. Failure: A reading outside this range or a significant deviation from the other injectors.
• Ignition Coil Secondary Resistance (3.7L I5) — expected: 6,000 - 10,000 Ohms. Failure: A reading outside of this range indicates a failure in the secondary windings.
• Ignition Coil Secondary Resistance (5.3L V8) — expected: 2,000 - 17,000 Ohms. Failure: A reading outside of this range indicates a failure in the secondary windings.
• Long-Term Fuel Trim (LTFT) at Idle — expected: -10% to +10%. Failure: Values consistently over +10% can indicate a vacuum leak; values consistently under -10% can indicate a leaking injector.

Hidden / Shadow Codes Worth Checking

• Misfire Current/History Counters: This is a live data parameter, not a formal trouble code. It shows a real-time count of misfire events for each cylinder, allowing a technician to see intermittent misfires on cylinder 5 even before the P0305 code becomes permanent or if a random misfire (P0300) is also present. (see via Requires a professional-grade scan tool with access to GM-specific live data PIDs, such as a GM Tech 2, GDS2, or equivalent high-end aftermarket scanner.)

Scan Tool Commands That Help

• GM Tech 2 / GDS2: Cylinder Power Balance Test — This function allows the technician to sequentially disable the fuel injector to each cylinder, one at a time. When a healthy cylinder is disabled, the engine RPM will drop noticeably. If cylinder 5's injector is disabled and there is little or no change in RPM, it confirms that cylinder 5 was not contributing properly to begin with.
• GM Tech 2 / GDS2: View Misfire Data (Current/History) — Essential for diagnosing intermittent misfires. By watching the live counters while driving under specific conditions (load, RPM), a technician can confirm exactly when and how often cylinder 5 is misfiring, which helps isolate the cause.

Wiring & Ground Locations

• G102 — Located at the left rear of the engine.. This is the primary ground point for the ignition coils on some GM engine configurations. A poor connection here can cause a weak spark and lead to misfires on one or more cylinders.
• G101 / G106 — G101 is on the lower left front of the engine block; G106 is on the front center of the frame cross rail. They are often jumpered together.. These grounds are critical for the Engine Control Module (ECM). A compromised ECM ground can cause a wide range of erratic engine behavior, including phantom misfire codes.
• G103 (V8) — On the front of the passenger side cylinder head.. This is a main engine-to-chassis ground. A poor connection can affect the entire engine's electrical system, including the ignition and injection components.

Real Owner Repair Stories

• YouTube user @kbtxtooldad (Chevy Silverado with 5.3L V8 (similar platform)) — Flashing check engine light and a stuttering or jerking sensation during acceleration, described as feeling like 'riding over a bump strip'.
  ❌ Tried (didn't work) Checking for loose spark plug wires., Replacing the spark plug wires and the spark plug for cylinder 5. This temporarily improved the symptoms, but the issue returned without a check engine light.
  ✅ What actually fixed it Replacing the ignition coil pack for cylinder 5 resolved the misfire completely.

OEM Part Supersession History

• ACDelco 41-985 → ACDelco 41-110 — Updated design for improved performance and longevity.
• N/A → ACDelco D1935E — Standard OEM replacement part for the 3.7L I5.
  Heads up: Part number D515C is for different GM V6 engines and is often confused. Using the wrong coil can lead to poor fitment and premature failure.
• GM 10457730 → ACDelco D585 — D585 is the service replacement part number for the original 'truck coil'.
  Heads up: To verify an authentic OEM replacement coil, look for the number '19005218' stamped on the metal bracket. Many aftermarket versions exist that may not have the same durability.
• N/A → ACDelco 217-3157 — Standard OEM replacement fuel injector for 2009-2012 3.7L I5 engines.

Model Year Variations Within This Range

• 2010-2012: The fuel injector wiring harness for the 3.7L I5 (GM Part #12602813) uses an EV6 style connector. This was a change from pre-2008 models, which used a different connector. This is relevant for anyone sourcing used parts or performing repairs that involve the injector harness.