P0308 on 2012 GMC Canyon 5.3L: Cylinder 8 Misfire Causes and Fixes

What's Unique About the 2012-2012 Gmc CANYON

While a P0308 misfire is a standard code, the 2012 GMC Canyon with the 5.3L V8 (engine codes LH8/LH9) has specific issues documented by GM. Technical Service Bulletins point to causes as simple as loose spark plug wires (TSB #PIP4819A) or as severe as worn camshaft lobes and lifters (TSB #PIP4138P and #19-NA-219). Unlike many other GM 5.3L V8s of the era, the version in the Canyon/Colorado does NOT have Active Fuel Management (AFM), so the common AFM lifter failure is not the cause here. However, non-AFM lifter and cam failures still occur. The placement of the V8 in the smaller Canyon engine bay can also make accessing cylinder 8 more challenging than in a full-size truck like a Sierra.

Diagnostic Flowchart

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

Symptoms You May Notice

• Rough idle or shaking/vibrating while stopped
• Hesitation or stumbling during acceleration
• Flashing or solid Check Engine Light
• Noticeable loss of engine power
• Smell of unburned gasoline from the exhaust
• A rhythmic ticking, chirping, or squeaking noise from the engine bay

Most Likely Causes

1. Loose or Damaged Spark Plug Wire 🔴 High Probability → Shop Spark Plug A GM Technical Service Bulletin (#PIP4819A) specifically calls out loose spark plug wires as a potential cause for misfires on this vehicle. A user on the Hummer4x4Offroad.com forum with the same engine reported a poorly seated plug wire caused their persistent misfire.
   How to confirm: Visually inspect the spark plug wire for cylinder 8. Ensure it is securely connected with an audible 'click' to both the ignition coil and the spark plug. Check for any signs of burns, arcing (white marks), or physical damage.
   Typical fix: Secure the loose wire or replace the entire set of spark plug wires if damage is found. It's best practice to replace them as a set to ensure balanced performance.
   Est. part cost: $40-$90
2. Worn or Fouled Spark Plug 🔴 High Probability → Shop Spark Plug
   How to confirm: Remove the spark plug from cylinder 8. Inspect it for a worn electrode, heavy carbon buildup, oil fouling, or cracks in the porcelain insulator. A healthy plug should have a light tan color.
   Typical fix: Replace the spark plug. It is highly recommended to replace all 8 spark plugs at the same time for balanced engine performance. The OEM recommended plug is an ACDelco Iridium plug.
   Est. part cost: $8-$20 per plug
3. Faulty Ignition Coil 🔴 High Probability → Shop Ignition Coil Ignition coils on GM V8 engines are a common failure item due to constant heat and vibration. Cylinder 8's location at the rear of the engine bay may subject it to higher ambient temperatures, potentially accelerating failure.
   How to confirm: Swap the ignition coil from cylinder 8 with another cylinder (e.g., cylinder 6, which is also on the passenger side). Clear the codes and drive. If the misfire code changes to P0306, the coil is bad.
   Typical fix: Replace the faulty ignition coil. It is typically held on by a single bolt on the valve cover bracket.
   Est. part cost: $30-$75
4. Clogged or Faulty Fuel Injector 🟡 Medium Probability → Shop Fuel Injector
   How to confirm: Listen to the injector with a mechanic's stethoscope or a long screwdriver; you should hear a consistent clicking sound. You can also use a 'noid light' to verify it's receiving an electrical pulse. Swapping the injector with another cylinder is a definitive but more labor-intensive test.
   Typical fix: Replace the faulty fuel injector. Some owners report success with using a high-quality fuel system cleaner for intermittent issues.
   Est. part cost: $45-$120

Rare But Worth Checking

• Worn Camshaft Lobe or Failed Lifter: → Shop Engine Camshaft This is a significant mechanical failure, but it is well-documented for this engine family in TSBs #PIP4138P and #19-NA-219. Symptoms often include a persistent ticking, chirping, or squeaking noise from the engine along with the misfire. Diagnosis requires removing the valve cover to inspect for loose rocker arms and may require a professional. This is a known issue even on the non-AFM versions of the 5.3L engine.
🎬 Watch: Why non-AFM lifters fail on the GM 5.3L engine
• Low Cylinder Compression: Internal engine problems like a bad valve, broken valve spring, worn piston rings, or a damaged head gasket can cause a loss of compression, leading to a misfire. A compression test is the definitive way to diagnose this.

Diagnosis Steps

1. Read the trouble codes with an OBD-II scanner and confirm P0308 is present. Note any other codes and check freeze frame data.
2. Check if the Check Engine Light is flashing. If so, limit driving to prevent catalytic converter damage.
3. Locate cylinder 8 at the rear passenger side of the engine.
4. Inspect the spark plug wire for cylinder 8. Ensure it's fully seated on the coil and plug (listen for a 'click'). Check for damage. (See TSB #PIP4819A)
5. Swap the ignition coil from cylinder 8 with cylinder 6 (the next one forward on the same bank). Clear the codes and run the engine. If the code changes to P0306, the coil is faulty.
🎬 Watch: A quick guide to diagnosing a Cylinder 8 misfire
6. If the misfire stays on cylinder 8, remove the spark plug. Inspect it for wear, fouling, or damage. Replace if necessary, preferably as a full set of 8.
7. If ignition parts are good, check the fuel injector. Listen for a steady clicking sound with a stethoscope. Use a noid light to confirm it's getting a signal from the PCM.
8. If the above steps don't reveal the cause, perform a cylinder compression test on cylinder 8 to rule out mechanical engine problems like bad rings or valves.
9. If compression is good and a persistent ticking noise is present, investigate the possibility of a worn camshaft or lifter, as noted in TSBs #PIP4138P and #19-NA-219. This involves removing the valve cover to check for excessive valvetrain play.

Parts You'll Likely Need

• Spark Plug (OEM #41-110) — Spark plugs are a routine maintenance item and a primary cause of misfires. A worn or fouled plug cannot create a strong enough spark. The OEM part is an ACDelco Iridium plug.
  Trusted brands: ACDelco, NGK
  OEM price range: $10-$15
  Aftermarket price range: $8-$12
• Ignition Coil (OEM #12570616) — Subjected to high heat and vibration, ignition coils are a common failure point that directly causes a misfire in a specific cylinder. This part number may be superseded by 12611424.
  Trusted brands: ACDelco, Delphi, Standard Motor Products
  OEM price range: $50-$75
  Aftermarket price range: $30-$60
• Spark Plug Wire Set (OEM #9748RR) — A loose connection or damaged wire prevents spark delivery, as highlighted in a manufacturer TSB. The V8 Canyon uses wires, unlike the 4 and 5-cylinder models.
  Trusted brands: ACDelco, NGK, Delphi
  OEM price range: $60-$90
  Aftermarket price range: $40-$70
• Fuel Injector (OEM #12613411) — A clogged or electrically failed injector will prevent fuel from entering cylinder 8, causing a misfire. Part number 12613411 is specified for 2010-2012 models.
  Trusted brands: ACDelco, Bosch, Standard Motor Products
  OEM price range: $70-$120
  Aftermarket price range: $45-$80

Related Codes That Often Appear With This One

• P0300 — If the misfire is intermittent or affects multiple cylinders, a P0300 (Random/Multiple Cylinder Misfire Detected) may be stored alongside P0308.

Technical Service Bulletins (TSBs) & Recalls

• PIP4819A: Notes that misfire codes can be caused by loose spark plug wires that need inspection and replacement.
• PIP4138P: Links engine misfires (P0300-P0308) and engine noise to a potentially worn camshaft lobe or lifter, requiring further mechanical diagnosis.
• PIP5628G: A general bulletin indicating that diagnosing misfires (P0300-P0308) may require assistance from the GM Technical Assistance Center (TAC), suggesting some causes can be difficult to isolate.

Platform-Specific Known Issues

• Loose Spark Plug Wires: → Shop Spark Plug TSB #PIP4819A specifically notes that misfire codes from P0300-P0308 can be caused by loose spark plug wires. This should be one of the first checks, ensuring the wire 'clicks' onto the plug and coil.
• Worn Camshaft/Lifters: → Shop Engine Camshaft TSB #PIP4138P and TSB #19-NA-219 indicate that engine noise (chirp, squeak, tick) and misfire codes (P0300-P0308) can be the result of a worn camshaft lobe or lifter. This is a known, albeit less common, mechanical issue on these non-AFM engines that must be considered if basic ignition and fuel system checks do not resolve the problem.

Mechanic-Grade Diagnostic Values

• Ignition Coil Primary Resistance — expected: 0.4 - 2.0 ohms. Failure: A reading outside this range suggests a faulty coil, though this test is not always conclusive for modern coils.
• Ignition Coil Secondary Resistance — expected: 6,000 - 10,000 ohms. Failure: A reading outside this range points to a failure in the secondary windings.
• Fuel Pressure (Scan Tool) — expected: ~400 kPa (~58 psi) at idle. Failure: Significantly lower pressure could indicate a weak fuel pump or clogged filter, affecting all cylinders but potentially triggering a single cylinder code first.
• Fuel Trim (STFT + LTFT) — expected: Between -10% and +10%. Failure: Consistently high positive numbers (e.g., +15% or more) on one bank can suggest a vacuum leak near that bank's intake runners, which could cause a lean misfire on a cylinder like #8.

Hidden / Shadow Codes Worth Checking

• Misfire History Counters: Not a specific code, but a data parameter available in professional scan tools that shows the number of misfire events per cylinder over a given drive cycle. This is far more detailed than the simple P-code and can show if other cylinders are misfiring occasionally, even if not enough to set a code. (see via GM Tech2, GDS2, or other professional-grade scanners with GM-specific software.)

Scan Tool Commands That Help

• GM Tech2 / GDS2: Misfire Graphic Display — To visually monitor misfire counts per cylinder in real-time. This helps confirm the misfire is isolated to cylinder 8 and isn't randomly occurring on others.
• Professional Scan Tool: Cylinder Power Balance Test — This test deactivates each cylinder one by one and measures the RPM drop. If disabling cylinder 8 results in little or no RPM drop, it confirms that cylinder was not contributing power.
• Professional Scan Tool: Fuel Injector Balance Test — To functionally test the fuel injector by commanding it to open and measuring the corresponding fuel pressure drop. This can definitively identify a clogged or weak injector.

Wiring & Ground Locations

• G102 — On the lower left (driver's) side of the engine block.. This is a primary ground for the ignition coils. A loose or corroded connection here can cause weak or intermittent spark on one or more cylinders, leading to misfires.
• G103 / G104 — G103 is on the lower left side of the engine; G104 is on the left side of the engine.. These are ground points for the Engine Control Module (ECM). A poor connection can cause erratic ECM behavior and a wide range of codes, including misfires.
• ECM Connector J2, Pin 48 — At the Engine Control Module (ECM), which is located at the right rear of the engine compartment.. This is the specific pin for the Fuel Injector 8 control circuit. The wire is typically Light Blue with a Red stripe. Testing for a pulsed ground signal at this pin can confirm if the ECM is commanding the injector to fire.

Real Owner Repair Stories

• Reddit user in r/ChevyTrucks (2011 Suburban (similar 5.3L V8 engine)) — P0308 misfire code.
  ❌ Tried (didn't work) Initial diagnosis focused on common ignition parts.
  ✅ What actually fixed it The user discovered the heater core quick-connect fittings were dripping coolant directly onto the #8 spark plug wire. Fixing the coolant leak and cleaning the wire resolved the P0308 code.

OEM Part Supersession History

• 12570616 (Ignition Coil) → 12611424, 12739916 — Standard part revision and consolidation by GM.
  Heads up: Aftermarket versions are often listed under the D510C part number. Ensure the coil is the correct square shape for this engine.
• 12613411 (Fuel Injector) → 12738848 — Standard part revision by GM.
  Heads up: This is a flex-fuel compatible injector. Ensure the replacement matches the vehicle's fuel system specifications.