P0303 on 2010-2013 Cadillac Escalade EXT: Cylinder 3 Misfire Causes and Fixes

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

The 2010-2013 Escalade EXT uses the 6.2L V8 (L94), an engine known for specific issues that can lead to a P0303 code. A GM Technical Service Bulletin (PIP4819A) directly points to loose spark plug wires as a potential cause for misfires on this platform. Additionally, this engine features Active Fuel Management (AFM), which deactivates certain cylinders under light loads. While cylinder 3 is not an AFM cylinder, issues within the AFM system, such as failing lifters on other cylinders (1, 4, 6, or 7), can cause significant engine imbalance, oil pressure variations, and trigger misfire codes on other cylinders. This is a well-documented weak point for this engine family.

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 shaky engine idle
• Hesitation or stumbling during acceleration, especially under load or going up an incline
• Noticeable loss of engine power
• Solid or flashing Check Engine Light
• Reduced fuel economy
• Engine may stall in some cases.
• A distinct ticking or tapping noise from the engine, which could indicate a lifter issue

Most Likely Causes

1. Faulty Ignition Coil 🔴 High Probability → Shop Ignition Coil Coil-on-plug systems are common failure points due to constant exposure to engine heat and vibration. Age and mileage are primary factors.
   How to confirm: Swap the ignition coil from cylinder 3 with another cylinder (e.g., cylinder 1). Clear the codes and drive the vehicle. If the code changes to P0301, the coil is bad. Visually inspect the coil for cracks in the plastic housing. 🎬 See how to diagnose faulty spark plugs and ignition coils.
   Typical fix: Replace the faulty ignition coil. Many owners choose to replace the corresponding spark plug at the same time as a preventative measure.
   Est. part cost: $45-$105
2. Worn or Fouled Spark Plug 🔴 High Probability → Shop Spark Plug Spark plugs are a regular maintenance item. The OEM ACDelco Iridium plugs (41-162) are specified, but wear, carbon buildup, or a cracked porcelain insulator can cause a weak or no-spark condition. Some owners have reported quality control issues with the newer 41-162 plugs compared to the older 41-110 version, noting the older version appeared to have superior manufacturing quality and resulted in a smoother idle.
   How to confirm: After confirming the coil is good, remove the spark plug from cylinder 3. Inspect it for wear, carbon buildup (which may appear wet with fuel), oil fouling, or damage to the ceramic insulator or electrode.
   Typical fix: Replace the spark plug. It is best practice to replace all 8 spark plugs if they are near the end of their 100,000-mile service life.
   Est. part cost: $8-$20 per plug
3. Loose or Damaged Spark Plug Wire 🟡 Medium Probability → Shop Spark Plug A specific Technical Service Bulletin (PIP4819A) was issued for these vehicles, citing loose-fitting spark plug wires as a cause for misfires. The connection at the coil or plug can become weak, causing intermittent spark.
   How to confirm: Visually inspect the spark plug wire for cylinder 3. Ensure it is securely 'clicked' onto both the ignition coil and the spark plug. Check for any signs of arcing (white or black marks) or physical damage to the boot or wire.
   Typical fix: Replace the spark plug wire. It is often recommended to replace the entire set of wires if they are original.
   Est. part cost: $50-$90 for a set
4. Clogged or Faulty Fuel Injector 🟡 Medium Probability → Shop Fuel Injector Fuel injectors can become clogged with deposits over time, preventing the correct amount of fuel from entering the cylinder. High resistance in the injector's electrical circuit can also cause a misfire without setting a specific injector code (P0203).
   How to confirm: If ignition components are confirmed good, you can swap the fuel injector from cylinder 3 with another cylinder. This is more labor-intensive. If the misfire code follows the injector, it is the cause. A mechanic can also perform a fuel injector balance test using a scan tool like the GM Tech 2.
   Typical fix: Replace the faulty fuel injector. Sometimes running a high-quality fuel system cleaner can resolve minor clogging.
   Est. part cost: $40-$120

Rare But Worth Checking

• Intake Manifold Gasket Leak: → Shop Engine Intake Manifold The intake manifold gasket can fail, creating a vacuum leak near cylinder 3. This leans out the air/fuel mixture and causes a misfire. A mechanic can perform a smoke test to confirm the leak.
• AFM Lifter Failure: → Shop Engine Valve Lifter While cylinder 3 is not an AFM cylinder, a collapsed lifter on an AFM cylinder (1, 4, 6, or 7) can cause significant engine imbalance and potentially trigger misfire codes on other cylinders. This is a major mechanical failure usually accompanied by a distinct ticking or tapping noise from the engine and often logs a P0300 (random misfire) code as well. Repair involves replacing the lifters and often the camshaft.
🎬 Watch: How to replace lifters and remove the cylinder head.
• Low Engine Compression: Internal mechanical problems like a worn piston ring, a burnt valve, or a head gasket leak can cause a loss of compression in cylinder 3. A compression and leak-down test is needed to diagnose this. One owner on a forum reported 82% leakage on cylinder #3, requiring head work.

Diagnosis Steps

1. Read the code with an OBD-II scanner and confirm P0303 is present. 🎬 Watch: A simple breakdown of the P0303 misfire code. Note any other codes, like P0300.
2. Check the Check Engine Light. If it's flashing, the misfire is severe and driving should be minimized to prevent catalytic converter damage.
3. Locate cylinder 3 (driver's side, second from the front).
4. Visually inspect the area. Look for obvious damage to the wiring for the ignition coil and fuel injector.
5. Swap the ignition coil from cylinder 3 with the coil from cylinder 1 (driver's side, front).
6. Clear the codes and start the engine. Let it run or drive it under the conditions that previously caused the misfire.
7. Re-scan the codes. If the code is now P0301, the ignition coil is faulty and needs replacement.
8. If the code remains P0303, the coil is likely good. Proceed to inspect the spark plug and wire.
9. Inspect the spark plug wire for cylinder 3 for a secure fit and any signs of damage, as noted in TSB PIP4819A.
10. Remove and inspect the spark plug from cylinder 3 for wear, fouling, or damage. A wet, fuel-soaked plug indicates a lack of spark, while a white, ashy plug could indicate a lean condition.
11. If ignition parts seem fine, the next step is to check the fuel injector. This can be done by swapping it with another cylinder, but this is more involved.
12. If all else fails, a mechanical compression and leak-down test is needed to check for internal engine problems like bad valves, piston rings, or a failed head gasket.

Parts You'll Likely Need

• Ignition Coil (OEM #12611424) — This is one of the most common failure items for a single-cylinder misfire. Heat and vibration cause the internal windings to fail over time.
  Trusted brands: ACDelco, Delphi, NGK, DENSO
  OEM price range: $70-$105
  Aftermarket price range: $45-$85
• Spark Plug (OEM #41-162) — As a standard wear item, the spark plug is a frequent cause of misfires and is often replaced along with the ignition coil as good practice. The 41-162 is the recommended Iridium plug for this engine.
  Trusted brands: ACDelco, NGK
  OEM price range: $12-$20
  Aftermarket price range: $8-$15
• Spark Plug Wire Set (OEM #9748GG) — A GM TSB specifically mentions loose wires as a cause for misfires on this engine. Wires can also degrade, causing weak spark or arcing.
  Trusted brands: ACDelco
  OEM price range: $70-$90
  Aftermarket price range: $50-$75

Related Codes That Often Appear With This One

• P0300 — P0300 indicates a random, multiple-cylinder misfire. It often appears alongside a specific cylinder code like P0303 if the misfire is intermittent, severe enough to affect engine stability, or if the root cause (like an AFM lifter) is systemic.

Technical Service Bulletins (TSBs) & Recalls

• PIP4819A: Mentions that engine misfires (P0300-P0308) can be caused by loose spark plug wires, requiring inspection and replacement.

Platform-Specific Known Issues

• TSB on Spark Plug Wires: GM issued Technical Service Bulletin #PIP4819A which states that misfire codes (including P0303) can be caused by spark plug wires that are not fully seated or have a loose connection. Technicians are advised to inspect the wires and replace any that are loose.
• AFM Lifter Concerns: The 6.2L L94 engine is equipped with Active Fuel Management (AFM), and the hydraulic lifters for the AFM cylinders (1, 4, 6, 7) are a known failure point. A collapsed lifter can cause a P0300 code and a loud ticking noise, and in some cases, may contribute to misfires on other cylinders due to overall engine instability.

Mechanic-Grade Diagnostic Values

• Fuel Injector Resistance — expected: 11-14 Ohms. Failure: A reading of 0 Ohms, infinite resistance, or a value significantly different from other injectors indicates a failure.
• Ignition Coil Primary Resistance — expected: 0.3 - 1.0 Ohms (general spec). Failure: A reading outside this range can suggest a faulty coil, though swapping coils is a more definitive test.
• Fuel Pressure (Key On, Engine Off) — expected: 50-60 PSI. Failure: Low pressure can cause lean misfires, but this would typically affect multiple cylinders and set a P0300 code.

Hidden / Shadow Codes Worth Checking

• Misfire History Counters: Dealer-level scan tools like GDS2 can display historical misfire counts for each cylinder, even if the misfires were not frequent enough to set a specific trouble code. This can help identify an intermittent issue on cylinder 3 before it becomes a constant fault. (see via GM GDS2 or equivalent professional scan tool)

Scan Tool Commands That Help

• GDS2 / Tech 2: Cylinder Power Balance / Injector Kill — This test disables one cylinder at a time and measures the corresponding drop in engine RPM. If disabling cylinder 3 causes little or no RPM drop compared to other cylinders, it confirms that cylinder 3 is not contributing power, isolating the fault.
• GDS2 / Tech 2: Fuel Injector Balance Test — After confirming spark is good, this test can identify a faulty injector. The tool pulses an injector for a set time and measures the pressure drop in the fuel rail. If the pressure drop for cylinder 3 is significantly different from the others, the injector is likely clogged or failing.

Wiring & Ground Locations

• G102 — Located at the left rear of the engine, on the cylinder head.. This ground is specifically for the 8 ignition coils. A poor connection here can cause weak or intermittent spark on any or all cylinders, including cylinder 3.
• G103 — Located on the front of the passenger side (right side) cylinder head.. This is an engine-to-chassis ground. While not specific to the coils, a poor connection can cause various electrical issues affecting engine performance.
• G104 — Located on the rear of the driver's side (left side) cylinder head, where a ground strap connects to the firewall.. This is a primary engine-to-body ground. A loose or corroded connection can create resistance in the ignition system's ground path, potentially leading to misfires.
• ECM Connector X2, Pin 52 — On the Engine Control Module (ECM).. This is the specific pin for the Ignition Control (IC) signal for cylinder 3. A technician can use this pin to test for the command signal from the ECM to the coil if a no-spark condition is present.

Real Owner Repair Stories

• YouTube channel 'Muhammad Mechanic' (Cadillac Escalade (year not specified, but similar GM V8 platform)) — Engine misfire with P0300 and a specific issue on one cylinder.
  ❌ Tried (didn't work) Initial diagnosis focused on common issues before testing the injector circuit.
  ✅ What actually fixed it The fuel injector for the misfiring cylinder 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.
• YouTube channel 'Alex The Car Doctor' (Cadillac Escalade with 6.2L V8) — Ticking and clicking noise from the engine, leading to misfires.
  ❌ Tried (didn't work) A previous shop failed to properly repair the issue.
  ✅ What actually fixed it A collapsed AFM lifter had failed, scoring the lifter bore in the engine block. The final repair involved having a machine shop repair the lifter bore and then reassembling the engine with new lifters and gaskets. This is an example of a major mechanical failure that can present as a misfire.

OEM Part Supersession History

• ACDelco 41-110 → ACDelco 41-162 — Design change and/or supplier change.
  Heads up: Both plugs are generally considered compatible. However, some users report the newer 41-162 is physically shorter than the 41-110. There are also anecdotal reports of better manufacturing quality and smoother engine performance with the older 41-110 plugs.
• ACDelco 12570616 → ACDelco 12611424 (D510C) — Part number update/supersession.
  Heads up: The coils are considered identical and interchangeable. Aftermarket listings often show one part number as a direct replacement for the other.

Model Year Variations Within This Range

• 2010-2013: The 2010 model year marked the introduction of the 6.2L L94 engine, which replaced the L9H. The key change was the addition of Active Fuel Management (AFM). Therefore, AFM-related failures, such as collapsed lifters, are a primary concern for this entire model year range but not for earlier 6.2L Escalades.