P0308 on 2002-2009 Cadillac Escalade EXT: Cylinder 8 Misfire Causes and Fixes

What's Unique About the 2002-2009 Cadillac ESCALADE EXT

While ignition issues are a common cause for any vehicle, the V8 engines in this generation of Escalade EXT (especially the 2007-2009 6.2L L92) are known for valvetrain problems. Specifically, models with Active Fuel Management (AFM), also called Displacement on Demand (DOD), are prone to lifter failure. A collapsed or stuck AFM lifter can cause a persistent misfire. A manufacturer TSB directly links P030x codes to worn camshaft lobes and lifters, making this a critical diagnostic path beyond simple ignition parts. The problem became so prevalent it resulted in class-action lawsuits against GM for the defective design.

Diagnostic Flowchart

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

Generation note: This range covers two generations of the Escalade EXT. The first (2002-2006) primarily used the 6.0L LQ9 V8, which featured the robust, round, heat-sink style ignition coils (Delphi D585). The second (2007-2009) used the 6.2L L92 V8, which often included Active Fuel Management (AFM) and switched to a square-style ignition coil. The AFM system is a frequent source of lifter failure, making the 2007-2009 models more susceptible to internal mechanical causes for this code. Notably, some sources suggest the L92 in the 2007-2008 Escalade did not have AFM, making it a desirable variant, with AFM being added in later years.

Symptoms You May Notice

• Rough or shaking idle
• Hesitation or stumbling during acceleration
• Noticeable loss of engine power
• Flashing or solid Check Engine Light
• Engine noise described as a tick, chirp, or squeak, especially on 2007+ models
• Strong smell of fuel from the exhaust

Most Likely Causes

1. Failed Ignition Coil 🔴 High Probability Coil-on-plug systems are common failure points due to constant heat and vibration. GM used two main coil styles: a round coil with a prominent heat sink (often called 'D585' style, common on 2002-2006 models) and a more compact square-style coil (common on 2007-2009 models). Visual inspection is necessary before ordering a replacement.
   How to confirm: Swap the ignition coil from cylinder 8 with another cylinder (e.g., cylinder 6 on the same passenger-side bank). Clear the codes and drive the vehicle. If the code changes to P0306, the coil is bad. 🎬 See how to swap ignition coils to isolate a faulty part. Cylinder 8 is the last cylinder on the passenger side.
   Typical fix: Replace the faulty ignition coil. It is often recommended to replace the spark plug at the same time. Many owners choose to replace all 8 coils at once if the vehicle has high mileage.
   Est. part cost: $35-$70
2. Worn Spark Plug or Defective Spark Plug Wire 🔴 High Probability
   How to confirm: After ruling out the coil, remove the spark plug from cylinder 8. Inspect it for wear (worn electrode), carbon fouling (black and sooty), or oil/coolant contamination. Inspect the spark plug wire for cracks, brittleness, or corrosion on the terminals.
   Typical fix: Replace the spark plug and/or wire. On these engines, ACDelco Iridium plugs are the recommended original equipment. It's best practice to replace all 8 plugs at the same time.
   Est. part cost: $10-$30
3. Failed AFM/DOD Lifter or Worn Camshaft 🟡 Medium Probability This is a well-documented issue, especially on 2007+ models with the 6.2L L92 engine's Active Fuel Management. A lifter can become mechanically stuck or collapse, preventing the valve from opening correctly. TSB #PIP4138P specifically points to checking for a worn camshaft lobe or lifter if standard diagnostics don't find the cause. A failed lifter can subsequently damage the camshaft lobe, requiring both to be replaced.
   How to confirm: If ignition and fuel system checks are inconclusive, listen for a persistent ticking noise from the passenger side of the engine. A compression test will show low or zero compression on cylinder 8. Definitive diagnosis requires removing the valve cover and potentially the cylinder head to inspect the valvetrain components.
   Typical fix: This is a major repair. It involves replacing the failed lifter(s) and often the camshaft. Many owners and shops perform an 'AFM/DOD delete' at this time, which involves replacing the AFM lifters, camshaft, and Valve Lifter Oil Manifold (VLOM) with standard, non-AFM components and reprogramming the ECM. This provides a permanent solution to the problem.
   Est. part cost: $400-$1500
4. Clogged or Faulty Fuel Injector ⚪ Low Probability
   How to confirm: Use a 'noid' light to confirm the injector is receiving an electrical pulse. If the pulse is present, swap the cylinder 8 injector with another cylinder (e.g. cylinder 6). If the misfire code follows the injector to P0306, the injector is faulty. A scan tool can also be used to perform an injector balance test.
   Typical fix: Replace the faulty fuel injector. It is often recommended to replace all four injectors on that bank, or all eight, to ensure balanced fuel delivery, especially on higher mileage vehicles.
   Est. part cost: $70-$160

Rare But Worth Checking

• Intake Manifold Gasket Leak: A vacuum leak near the cylinder 8 intake runner can lean out the air/fuel mixture, causing a misfire. This would typically be accompanied by a hissing sound and possibly other lean condition codes (e.g., P0171, P0174).
• Low Engine Compression: Besides a failed lifter, low compression can be caused by issues like a worn piston ring, a bent valve, or a failed head gasket. A cylinder leak-down test can help pinpoint the source of the compression loss.
• Bad Ground Connection: A loose or corroded ground strap for the engine block or cylinder head can cause intermittent or widespread misfires on one or both banks. On GMT800/900 trucks, a common failure point is the ground strap located at the rear of the passenger-side cylinder head, which is difficult to access.
• Failed Valve Lifter Oil Manifold (VLOM): On AFM-equipped engines (2007+), the VLOM directs oil pressure to activate/deactivate the special lifters. It contains solenoids and small filters that can clog or fail, leading to a lifter not functioning correctly and causing a misfire. This is often replaced during an AFM lifter repair.

Diagnosis Steps

1. Check if the Check Engine Light is solid or flashing. A flashing light indicates a severe misfire requiring immediate attention to prevent catalytic converter damage.
2. Use an OBD-II scanner to confirm P0308 and check for any other codes like P0300 or P050D.
3. Identify Cylinder 8: It is the rearmost cylinder on the passenger side of the engine.
4. Test the ignition system: Swap the ignition coil from cylinder 8 with cylinder 6 (an easier-to-access cylinder on the same bank). Clear the codes and run the engine. If the code changes to P0306, the ignition coil is faulty.
5. If the misfire remains on cylinder 8, inspect the spark plug for wear or fouling and the plug wire for damage. Replace as needed.
6. Check the fuel injector: Use a 'noid light' to verify it's receiving a signal. If it is, consider swapping the injector with another cylinder to see if the misfire follows.
7. Listen for abnormal engine noises. A persistent ticking from the passenger-side valve cover area is a strong indicator of a valvetrain problem (lifter/camshaft).
8. Check for bad grounds. Inspect the main engine-to-chassis ground straps and the smaller ground strap located at the back of the passenger-side cylinder head. A poor connection here is a known cause of misfires on this bank.
9. If other tests are inconclusive, perform a compression test on cylinder 8. A significantly lower reading compared to other cylinders points to a mechanical issue.
10. If a mechanical issue is suspected, remove the valve cover to visually inspect the rocker arms, pushrods, and valve springs for cylinder 8, as suggested by TSB #PIP4138P.

Parts You'll Likely Need

• Ignition Coil (OEM #ACDelco D585 (Round 'heat sink' style, pre-2007) or 12570616 (Square style, 2007+)) — This is the most common failure point for a single-cylinder misfire. Heat and vibration cause the internal windings to fail over time. The D585 coils are often considered more robust by enthusiasts.
  Trusted brands: ACDelco, Delphi, NGK
  OEM price range: $50-$80
  Aftermarket price range: $30-$55
• Spark Plug (OEM #ACDelco 41-110 or 41-962 (Iridium, check specific year)) — A worn or fouled spark plug cannot create a strong enough spark for proper combustion. It's a standard maintenance item that is critical for ignition health.
  Trusted brands: ACDelco, NGK
  OEM price range: $10-$20
  Aftermarket price range: $5-$15
• AFM/DOD Lifter (OEM #12645725) — The Active Fuel Management lifters are a known weak point, prone to collapsing or sticking, causing a misfire. When one fails, it is recommended to replace all AFM lifters, and many owners opt for a full AFM delete.
  Trusted brands: ACDelco, Sealed Power, Elgin
  OEM price range: $50-$90
  Aftermarket price range: $25-$50

Related Codes That Often Appear With This One

• P0300 — If the condition causing the P0308 is intermittent or beginning to affect other cylinders, a P0300 (Random Misfire) code may also be stored.
• P050D — This code for 'Cold Start Rough Idle' is often seen alongside misfire codes on these GM trucks and is mentioned in TSBs related to injector and lifter issues.

Technical Service Bulletins (TSBs) & Recalls

• PIP4138P: Points to a worn camshaft lobe or lifter as a potential cause for P0300-P0308 codes when other diagnostics fail.
• PIP5628C: Provides diagnostic aid information for technicians when encountering misfire codes P0300-P0308.
• 18-NA-137: While for later models, it highlights a known issue of fuel smells and misfires caused by injector seal problems, which can be relevant.

Platform-Specific Known Issues

• AFM/DOD Lifter Failure: On 2007-2009 models, the Active Fuel Management system lifters are a notorious point of failure. They can become stuck or collapse, leading to a misfire and a distinct ticking noise. TSB #PIP4138P directly addresses this, advising technicians to inspect for worn camshaft lobes and lifters when a P030x code cannot be solved by ignition or fuel system repairs. This is a significant repair that often leads owners to perform a full 'AFM delete' to prevent future issues.
• Ignition Coil Style Confusion: The 2002-2009 range spans a change in ignition coil design. Early models (approx. 2002-2006) used a round coil with a metal heat sink, often called the Delphi D585 or 'LS truck coil,' which is highly regarded. Later models (approx. 2007-2009) used a more compact, square-shaped coil. It is critical to visually verify which coil is on the vehicle before ordering a replacement.
• Corroded Ground Straps: Like their Chevrolet and GMC platform mates, the Escalade EXT can suffer from poor ground connections, especially the strap located on the back of the passenger-side cylinder head. This ground is for the ignition coil harness, and if it becomes loose or corroded, it can cause a misfire on any or all of the cylinders on that bank (2, 4, 6, 8).

Mechanic-Grade Diagnostic Values

• Ignition Coil Primary Resistance (Square Style, 2007+) — expected: 0.660 ohms. Failure: Significant deviation from the expected resistance.
• Ignition Coil Secondary Resistance (Square Style, 2007+) — expected: 6.1k Ohms. Failure: Significant deviation from the expected resistance.
• Ignition Coil Primary Resistance (Round 'D514A' Style, pre-2007) — expected: 0.820 ohms. Failure: Significant deviation from the expected resistance.
• Ignition Coil Secondary Resistance (Round 'D514A' Style, pre-2007) — expected: 7.10k Ohms. Failure: Significant deviation from the expected resistance.
• Fuel Injector Resistance (6.2L) — expected: ~1.5 Ohms. Failure: A reading of 2.2 Ohms on the faulty injector compared to 1.5 Ohms on good injectors indicated a problem.

Hidden / Shadow Codes Worth Checking

• Misfire Current Counters: This is not a DTC, but a live data parameter showing a running count of misfire events for each individual cylinder. It is far more sensitive than the P030x codes and can reveal intermittent misfires before they are severe enough to trigger a light. (see via A GM-specific scan tool like a Tech 2 or GDS2, or some high-end professional scanners.)

Scan Tool Commands That Help

• Tech 2 / GDS2: Injector Balance Test — This function allows the technician to disable one injector at a time to see the corresponding drop in RPMs. If disabling the cylinder 8 injector causes no change in RPM, it confirms that the injector was not contributing, pointing to a problem with it or its circuit.
• Tech 2 / GDS2: Cylinder Deactivation — For AFM-equipped engines, this command can be used to manually activate and deactivate the AFM solenoids and lifters to test their function without having to meet specific driving conditions. This can help diagnose a stuck lifter or faulty VLOM solenoid.

Wiring & Ground Locations

• G103 — Front of the right (passenger side) cylinder head.. This is a primary ground point for multiple engine components, including the ignition coil bank on that side. A loose or corroded G103 can cause weak spark and misfires on cylinders 2, 4, 6, and 8.
• G104 — Front of the left (driver side) cylinder head.. While not on the same bank as cylinder 8, a poor ground here can cause electrical noise and erratic behavior in the ECM, potentially leading to misdiagnosed misfires. It grounds the other bank of ignition coils.
• Engine Harness Chafe Point 1 — Driver's side, where the main engine harness can rub against the ECM/TCM bracket.. Vibration can cause the harness to chafe against the sharp edge of the bracket, potentially shorting ignition control or injector control wires, leading to misfires. GM issued a bulletin regarding this issue.
• Engine Harness Chafe Point 2 — Driver's side, where the harness may contact the upper control arm or a shock tower bolt.. Similar to the ECM bracket chafe, engine movement can cause the harness to rub through on these components, causing shorts that can lead to misfires or other electrical issues.

Real Owner Repair Stories

• BobIsTheOilGuy forum user (2007 Escalade 6.2L with 335,000 km) — P0308 misfire, but only at idle after about 15-20 seconds. Stabilitrak/Traction Control messages would appear, and the check engine light would flash if idling continued. Drove perfectly on the highway.
  ❌ Tried (didn't work) Swapping ignition coils, Swapping spark plugs and wires, Installing a brand new spark plug in cylinder 8
  ✅ What actually fixed it The user did not post the final fix, but a mechanic diagnosed it as a failing AFM lifter, which is consistent with the symptoms of an idle-only misfire that disappears under load.
• YouTube video by 'Julio Auto MekaniKo' (2016 Cadillac Escalade (Note: Newer model, but same engine family and issue)) — P0308 misfire on cylinder 8.
  ❌ Tried (didn't work) Initial assumption of common lifter/cam failure.
  ✅ What actually fixed it A cylinder leak-down test showed significant leakage. Upon inspection, the spark plug was wet with coolant, indicating a cracked cylinder head or failed head gasket, not the more common AFM lifter failure.

OEM Part Supersession History

• Elgin HL-7011 (AFM Lifter) → Elgin HL-7025 (DFM Lifter) — A newer lifter was designed for the newer Dynamic Fuel Management (DFM) systems.
  Heads up: The new DFM lifter (HL-7025) is backward compatible and can be used in older AFM engines. However, the original AFM lifter (HL-7011) can ONLY be used in AFM applications and will not work in the newer DFM engines.
• ACDelco 12570616 (Square Ignition Coil) → ACDelco 12611424 — Standard part revision and supplier changes over the production run.

Model Year Variations Within This Range

• 2007-2008 vs 2009+: The 6.2L L92 engine in 2007-2008 Escalades often did not have Active Fuel Management (AFM), making them less prone to the common lifter failure. In 2009, the engine was updated to the L9H, which was a flex-fuel variant and more commonly included AFM. The L94 used from 2010-2014 always had AFM.
• 2002-2006 vs 2007-2009: The ignition coil design changed. Early models (pre-2007) used a round, heat-sink style coil (e.g., ACDelco D585), while later models (2007+) used a more compact, square-style coil (e.g., ACDelco 12570616). The parts are not interchangeable.