P0308 on 2010-2013 Cadillac Escalade EXT: Cylinder 8 Misfire Causes & Fixes

What's Unique About the 2010-2013 Cadillac ESCALADE EXT

The 6.2L V8 engine (RPO L94) in this generation of Escalade is generally robust, but it has specific vulnerabilities that can lead to a P0308 code. GM issued a Technical Service Bulletin (TSB #PIP4819A) specifically for loose spark plug wires causing misfires on these trucks. More significantly, this engine features Active Fuel Management (AFM), a system that deactivates cylinders to save fuel. The AFM lifters are a known weak point and can fail, leading to misfires, a distinct ticking noise, and eventually camshaft damage, a problem also documented in manufacturer TSBs.

Diagnostic Flowchart

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

Symptoms You May Notice

• Flashing or solid Check Engine Light
• Rough or vibrating engine idle
• Hesitation or stumbling during acceleration
• Noticeable loss of engine power
• Reduced fuel economy
• A rhythmic ticking, chirping, or squeaking noise from the engine, especially one that increases with RPM
• Smell of raw fuel from the exhaust
• "Service StabiliTrak" message may appear on the dash, as the system is often disabled when a misfire is detected

Most Likely Causes

1. Loose or Faulty Spark Plug Wire 🔴 High Probability A specific TSB (#PIP4819A) was issued by GM for this exact problem on these vehicles, indicating it's a known issue where the wire becomes loose at the ignition coil.
   How to confirm: Visually inspect the spark plug wire for cylinder 8 (the rearmost cylinder on the passenger side). Ensure it is securely clicked onto both the spark plug and the ignition coil. Check for any signs of damage, arcing (white marks), or corrosion. A loose connection at the coil is the specific concern noted in the TSB.
   Typical fix: Securely reconnect or replace the spark plug wire. It is best practice to replace the full set if they are old, 🎬 See this walkthrough for replacing Escalade spark plugs and wires. as others may fail soon.
   Est. part cost: $10-$25 for a single wire, $60-$120 for a full set.
2. Worn or Fouled Spark Plug 🔴 High Probability
   How to confirm: Remove the spark plug from cylinder 8. Inspect it for wear (worn electrode), oil/carbon fouling, or a cracked insulator. A fuel-soaked plug points to an ignition or injector issue. You can also swap it with a plug from a known good cylinder (e.g., cylinder 6) and see if the misfire code moves to P0306.
   Typical fix: Replace the spark plug. It's best practice to replace all 8 plugs if they are near the end of their service life (typically around 100,000 miles).
   Est. part cost: $8-$20 per iridium plug.
3. Defective Ignition Coil 🟡 Medium Probability
   How to confirm: Swap the ignition coil from cylinder 8 with one from another cylinder (e.g., cylinder 6). Clear the codes and drive the vehicle. If the code changes to P0306, the ignition coil is faulty. This is a very reliable diagnostic step.
   Typical fix: Replace the faulty ignition coil. They are mounted individually and are easy to access.
   Est. part cost: $35-$95 for one OEM-quality coil.
4. Failed AFM Lifter 🟡 Medium Probability The Active Fuel Management (AFM) system lifters are a well-documented failure point on these GM V8 engines, as noted in multiple TSBs. The lifters can become stuck or collapse, preventing the valve from opening correctly, which causes a misfire.
   How to confirm: This often presents with a persistent ticking or chirping noise that follows engine RPM. A mechanic can perform a cylinder drop-out test or may need to remove the valve cover to inspect the valvetrain components for lack of movement on the cylinder 8 rocker arms. Low compression on that cylinder is another strong indicator.
   Typical fix: This is a major repair involving replacing all AFM lifters (and often the non-AFM lifters as well) and frequently the camshaft if it has been damaged by the failed lifter roller. Many owners opt to install an AFM-delete kit to prevent future failures.
   Est. part cost: $400-$1000+ for lifters, camshaft, and associated gaskets.
5. Clogged or Faulty Fuel Injector ⚪ Low Probability
   How to confirm: Listen for the injector's clicking sound with a mechanic's stethoscope. You can also test its resistance with a multimeter or swap it with another cylinder's injector to see if the misfire follows. A fuel-soaked spark plug can indicate an injector stuck open.
   Typical fix: Replace the faulty fuel injector. It's often recommended to replace them as a set if they are high mileage.
   Est. part cost: $50-$150 for one injector.

Rare But Worth Checking

• Worn Camshaft Lobe: This is almost always a direct result of a failed lifter roller. TSB #PIP4138P and others explicitly link misfire codes to worn camshaft lobes. If a lifter has failed, the camshaft must be inspected for damage, as replacing only the lifter will result in a repeat failure.
• Low Cylinder Compression: Caused by issues like a bad valve, broken valve spring, or worn piston rings. A compression test and cylinder leak-down test are needed to confirm this. This indicates a serious internal engine mechanical problem.
• Cracked Cylinder Head / Blown Head Gasket: While rare, a coolant leak into the cylinder can cause a misfire. A key symptom is a spark plug that appears 'steam cleaned' or is wet with coolant, along with coolant loss and potential white smoke from the exhaust.

Diagnosis Steps

1. Read the code with an OBD-II scanner to confirm P0308 and check for any other codes. 🎬 Watch: A guide to diagnosing and fixing P0308 misfire codes. Note if the Check Engine Light is flashing.
2. Locate cylinder 8. On the 6.2L V8, it is the rearmost cylinder on the passenger's side of the engine.
3. Inspect the spark plug wire for cylinder 8. Per TSB #PIP4819A, ensure it's fully seated on the coil and plug. Check for any damage or signs of arcing.
4. Swap the ignition coil from cylinder 8 with the coil from cylinder 6 (the cylinder in front of it). Clear the codes and drive. If the code changes to P0306, the coil is bad.
5. If the code remains P0308, remove and inspect the spark plug. Look for wear, fouling, or damage. A fuel-soaked plug suggests a fuel or spark issue. Swap the plug with cylinder 6, clear codes, and drive. If the code moves to P0306, the plug is bad.
6. If the misfire is still on cylinder 8, the issue is likely fuel or mechanical. Listen for a steady clicking sound from the injector with a stethoscope. Check the wiring to the fuel injector.
7. Listen for a persistent ticking or chirping noise from the engine that changes with RPM. This is a classic symptom of a failed AFM lifter.
8. If a lifter failure is suspected, a professional should confirm. This may involve removing the valve cover to check for a collapsed lifter or bent pushrod.
9. Perform a compression test on cylinder 8 to rule out base engine mechanical problems like bad rings or valves. A reading significantly lower than other cylinders indicates a mechanical fault.

Parts You'll Likely Need

• Spark Plug (OEM #12621258 (superceded by 41-110)) — Spark plugs are a common maintenance item and a frequent cause of misfires. The original part number was often 12571165 or 12621258, both serviced by ACDelco 41-110.
  Trusted brands: ACDelco, NGK
  OEM price range: $10-$20
  Aftermarket price range: $8-$15
• Ignition Coil (OEM #12573190 (superceded by ACDelco D510C)) — Ignition coils are a common failure point that directly causes a misfire on a single cylinder. The ACDelco D510C is the common service replacement.
  Trusted brands: ACDelco, Delphi, Standard Motor Products
  OEM price range: $75-$95
  Aftermarket price range: $30-$60
• Spark Plug Wire Set (OEM #9748UU) — A loose or damaged spark plug wire is a specific cause of misfires on this vehicle, as noted in TSB #PIP4819A.
  Trusted brands: ACDelco, NGK
  OEM price range: $80-$120
  Aftermarket price range: $50-$90

Related Codes That Often Appear With This One

• P0300 — If the misfire is intermittent or starting to affect other cylinders, a P0300 (Random/Multiple Misfire) code may appear alongside P0308. This is common with AFM lifter issues.
• P050D — This code for 'Rough Idle Off Cold Start' is mentioned in TSB #PIP5628C in conjunction with misfire codes, suggesting a potential link in the diagnostic process, often related to fuel system or injector issues.
• P219B — This code indicates an air-fuel ratio imbalance on Bank 2 (which includes cylinder 8). A misfire is a primary cause of this imbalance, so fixing the P0308 will often resolve the P219B.

Technical Service Bulletins (TSBs) & Recalls

• PIP4819A: Notes that misfire codes P0300-P0308 can be caused by loose spark plug wires.
• PIP4138P: Links misfire codes P0300-P0308 and engine noise to potential worn camshaft lobes or lifter issues.
• PIP5628C: Mentions that codes P0300-P0308 may be seen with P050D (Rough Idle Off Cold Start) and provides diagnostic guidance.

Platform-Specific Known Issues

• AFM Lifter Failure: The Active Fuel Management (AFM) system in the 6.2L L94 V8 is the most significant and costly potential cause for a P0308. The system deactivates cylinders 1, 4, 6, and 7, but the complexity can lead to failure of any lifter. When a lifter collapses or its roller is damaged, it fails to actuate the valve properly, causing a persistent misfire. This is often accompanied by a distinct ticking sound. One forum user with a GMC Yukon Denali (a platform mate) experienced this failure at 78k miles, describing it as the 'passenger side AFM lifter left the chat'. The repair is labor-intensive, requiring removal of the cylinder head and, if the camshaft is damaged, removal of the engine front cover and timing components.
• Loose Spark Plug Wires: GM TSB #PIP4819A specifically calls out loose spark plug wires at the ignition coil as a cause for misfires (P0300-P0308) on this and many other V8-equipped GM trucks and SUVs from the era. Before performing more complex diagnostics, ensuring the #8 wire is securely clicked onto the coil is a critical and simple first step.

Mechanic-Grade Diagnostic Values

• Fuel Injector Resistance — expected: 11-14 Ohms. Failure: A reading of 0 Ohms or infinite resistance (open loop) indicates a failed injector. A significantly different reading from other injectors also points to a problem.
• Ignition Coil Primary Resistance — expected: 0.8 to 2.0 Ohms (general spec). Failure: A reading outside of the typical range suggests an internal coil issue. However, swapping the coil with a known good cylinder is the most definitive test.
• Fuel Pressure (Key On, Engine Off) — expected: 50-60 PSI. Failure: Low fuel pressure can cause lean misfires, but it would typically affect multiple cylinders and set a P0300 code, not just P0308.

Hidden / Shadow Codes Worth Checking

• Mode 6, Test ID $A2-$AB, Component ID $08: This is not a shadow code, but rather raw data from the OBD-II system's Mode 6. A technician can view the misfire counts for each cylinder, including cylinder 8 (Component ID $08), over the current and last 10 driving cycles. This helps quantify the severity and frequency of the misfire before it crosses the threshold to set the P0308 code. (see via A professional scan tool with Mode 6 data capability.)

Scan Tool Commands That Help

• GDS2 / Tech2: Cylinder Power Balance — This test graphically displays the contribution of each cylinder to the crankshaft's rotational speed. For a P0308, the graph will show a significant drop for cylinder 8, confirming it is not contributing power. This is useful to see the misfire in real-time.
• GDS2 / Tech2: Fuel Injector Control — This bidirectional command allows a technician to disable the fuel injector for cylinder 8. If disabling the injector causes no change in engine RPM or smoothness, it confirms that the cylinder was not contributing in the first place, pointing away from the injector and towards a spark or mechanical issue.
• GDS2 / Tech2: AFM Cylinder Deactivation Test — If an AFM lifter failure is suspected, this function allows a technician to command the AFM system on and off while monitoring misfire counters. This can help isolate whether the misfire is directly related to the state of the AFM system.

Wiring & Ground Locations

• G104 — Rear of the left (driver's side) cylinder head.. This is a primary engine-to-chassis ground. A loose or corroded connection here can cause a host of electrical issues, including weak spark or erratic sensor readings that could contribute to misfires.
• G103 — Front of the left (driver's side) cylinder head.. Another critical engine ground point. Both G103 and G104 should be checked, cleaned, and tightened when diagnosing any electrical or ignition-related fault code.
• Ignition Controls - Ignition System Coils 2, 4, 6, and 8 — Vehicle wiring harness schematic.. This specific wiring diagram shows the power, ground, and signal wires for the Bank 2 ignition coils, including cylinder 8. It is essential for checking voltage, ground integrity, and signal from the ECM directly at the coil connector.
• Fuel Controls - Fuel Injectors — Vehicle wiring harness schematic.. This diagram details the wiring for all eight fuel injectors, allowing a technician to trace the control wires for the cylinder 8 injector back to the ECM to check for opens or shorts.

Real Owner Repair Stories

• YouTube channel 'Muhammad Mechanic' (Cadillac Escalade (year not specified, but similar engine platform)) — Engine misfire, P0300 and a specific issue on cylinder 8.
  ❌ Tried (didn't work) Initial diagnosis pointed towards common issues, but the mechanic proceeded to test the injector circuit.
  ✅ What actually fixed it The fuel injector for cylinder 8 was faulty. A resistance test showed it was out of spec (2.2 ohms) compared to a good cylinder (1.5 ohms). Replacing the injector resolved the issue.

OEM Part Supersession History

• 12570616 → 12611424, ACDelco D510C — Standard part evolution and consolidation.
  Heads up: The original coils were square-shaped. The D510C is also a square-shaped coil and is the correct service replacement. Some GM trucks used a round 'Melco' style coil; these are not interchangeable. Always verify the shape of the original coils.

Model Year Variations Within This Range

• 2010-2014: The 6.2L engine in the 2010-2013 Escalade EXT is the L94. This engine is part of the Gen 4 small block family and is mechanically similar to the L92 and L9H but is unique in that it includes both Variable Valve Timing (VVT) and Active Fuel Management (AFM). The AFM system is the primary source of the lifter-related failures that can cause a P0308 code on this specific platform.