P0303 on 2010-2013 GMC Savana: Cylinder 3 Misfire Causes and Fixes

What's Unique About the 2010-2013 Gmc SAVANA

For the 2010-2013 GMC Savana with a V8 engine, the ignition system is a primary suspect for any misfire code. These workhorse vans accumulate high mileage, leading to wear on ignition components. A GM Technical Service Bulletin (TSB) for the 2010 model year specifically points to loose spark plug wires as a potential cause for a range of misfire codes, including P0303, making it a crucial first check for owners. Furthermore, some of these V8 engines are equipped with Active Fuel Management (AFM), which can lead to lifter failure. A collapsed or stuck AFM lifter is a known cause of misfires on these engines and can present as a P0303 code, often accompanied by a distinct ticking noise.

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 idle
• Hesitation or stumbling during acceleration
• Flashing Check Engine Light
• Reduced engine power
• Poor fuel economy
• Noticeable smell of gasoline from the exhaust
• Exhaust that smells like rotten eggs, indicating potential catalytic converter damage

Most Likely Causes

1. Faulty Spark Plug Wire 🔴 High Probability → Shop Spark Plug A specific Technical Service Bulletin (PIP4819A) was issued for 2010 models regarding loose spark plug wires causing misfires. Wires also degrade from heat and age, a common issue on high-mileage work vans.
   How to confirm: Visually inspect the wire for cylinder 3 for damage, cracks, or burns. Ensure it is securely connected at both the spark plug and the ignition coil. You can test resistance with a multimeter if you have one.
   Typical fix: Replace the spark plug wire. It is best practice to replace all wires as a set to ensure reliability.
   Est. part cost: $40-$100
2. Worn or Fouled Spark Plug 🔴 High Probability → Shop Spark Plug
   How to confirm: Remove the spark plug from cylinder 3. Inspect it for wear on the electrode, carbon fouling, oil, or cracks in the ceramic. A simple diagnostic test is to swap the cylinder 3 spark plug with one from another cylinder (e.g., cylinder 1). If the code changes to P0301, the spark plug is the culprit.
   Typical fix: Replace the spark plug. It is highly recommended to replace all spark plugs at the same time 🎬 Watch: Step-by-step guide to replacing spark plugs on your Savana. for even performance.
   Est. part cost: $5-$15 per plug
3. Failed Ignition Coil 🟡 Medium Probability → Shop Ignition Coil
   How to confirm: Swap the ignition coil from cylinder 3 with the coil from another cylinder (e.g., cylinder 1). Clear the codes and run the engine. If the code returns as P0301, the ignition coil is faulty.
   Typical fix: Replace the faulty ignition coil. While some recommend replacing all coils, it's common to replace only the failed one.
   Est. part cost: $30-$75
4. Clogged or Faulty Fuel Injector ⚪ Low Probability → Shop Fuel Injector
   How to confirm: This is more complex. A mechanic can perform a fuel injector balance test. A DIY method is to listen for the injector's clicking sound with a mechanic's stethoscope or a long screwdriver. You can also swap injectors between cylinders, but this is more labor-intensive than swapping coils or plugs.
   Typical fix: Replace the faulty fuel injector. Sometimes, professional fuel system cleaning can resolve a clogged injector.
   Est. part cost: $50-$120

Rare But Worth Checking

• Intake Manifold Gasket Leak: → Shop Engine Intake Manifold A vacuum leak near the intake runner for cylinder 3 can lean out the air/fuel mixture, causing a misfire. This can be diagnosed with a smoke test.
• Low Engine Compression: Internal engine issues like a worn piston ring, a burnt valve, or a failing lifter can cause a loss of compression in cylinder 3. This is a serious issue diagnosed with a compression test and a cylinder leak-down test.
• Active Fuel Management (AFM) Lifter Failure: → Shop Engine Valve Lifter On engines equipped with AFM (also known as Displacement on Demand or DOD), the specialized lifters can become stuck or collapse. This is a well-documented problem that leads to misfires and can cause camshaft damage if not addressed. Symptoms often include a persistent ticking noise. TSB #15-06-01-002F addresses this issue, which can cause a P0300 or a single-cylinder misfire code.

Diagnosis Steps

1. Read the trouble codes with an OBD-II scanner. Note P0303 and any other codes present, such as P0300.
2. Locate cylinder 3 on your engine. For the V8s, it's the second cylinder from the front on the driver's side.
3. Per TSB #PIP4819A, inspect the spark plug wire for cylinder 3. Ensure it is fully seated on both the spark plug and the ignition coil. Check for any visible damage.
4. Remove the ignition coil and spark plug from cylinder 3. Inspect the spark plug for wear, fouling, or damage.
5. To confirm the cause, swap components. First, swap the spark plug from cylinder 3 with cylinder 1. Clear the codes and drive. If code P0301 appears, you need a new spark plug.
6. If the code remains P0303, swap the ignition coil from cylinder 3 with cylinder 1. Clear codes and drive. If P0301 appears, you need a new ignition coil.
🎬 See how to diagnose and fix a P0303 misfire yourself.
7. If the misfire persists on cylinder 3, check for spark using an inline spark tester to definitively rule out the entire ignition circuit for that cylinder.
8. If spark is present, the issue may be the fuel injector. Listen for a consistent clicking sound from the injector with a stethoscope.
9. If ignition and fuel delivery seem okay, the problem may be mechanical. Listen for a persistent ticking noise that could indicate a failed lifter. At this point, performing an engine compression test is the next step to check for internal engine problems.

Parts You'll Likely Need

• Spark Plug (OEM #ACDelco 41-110) — Spark plugs are a routine maintenance item and the most common failure point for a single-cylinder misfire.
  Trusted brands: ACDelco, NGK
  OEM price range: $8-$15
  Aftermarket price range: $5-$12
• Ignition Coil (OEM #ACDelco D585) — The individual coil-on-plug for cylinder 3 can fail, preventing spark. It's the second most likely cause after the spark plug.
  Trusted brands: ACDelco, Delphi
  OEM price range: $50-$90
  Aftermarket price range: $30-$75
• Spark Plug Wire Set (OEM #ACDelco 9748RR) — A GM TSB specifically mentions loose wires as a cause for misfires on these vehicles. Wires degrade over time and are often replaced with spark plugs.
  Trusted brands: ACDelco, Delphi
  OEM price range: $60-$120
  Aftermarket price range: $40-$100

Related Codes That Often Appear With This One

• P0300 — If the misfire is intermittent or affects multiple cylinders, a P0300 (Random/Multiple Cylinder Misfire) code may be stored alongside P0303. This can sometimes point towards a failing AFM lifter.

Technical Service Bulletins (TSBs) & Recalls

• PIP4819A - Relates to Service Engine Soon light and engine misfires (DTCs P0300-P0308) due to loose spark plug wires.
• 15-06-01-002F - Addresses engine misfires (P0300) and ticking noises resulting from a mechanically collapsed or stuck Active Fuel Management (AFM) lifter.

Platform-Specific Known Issues

• A known issue documented in TSB #PIP4819A involves loose spark plug wires causing misfires on 2010 models. The bulletin advises technicians to inspect the spark plug wires and replace any that are loose.
• The V8 engines with Active Fuel Management (AFM) are prone to lifter failure. A collapsed or stuck lifter can cause a single-cylinder misfire (like P0303) or a random misfire (P0300), often accompanied by a ticking noise from the engine. 🎬 Watch: Tips for diagnosing ticking noises and bad AFM lifters. This is a more serious mechanical issue that goes beyond simple ignition component replacement.

Mechanic-Grade Diagnostic Values

• Fuel Pressure (Key On, Engine Off) — expected: 60-66 psi (415-455 kPa). Failure: Pressure below 60 psi, or pressure that drops quickly after the pump primes, indicates a problem with the pump, regulator, or a leak.
• Ignition Coil Primary Resistance (ACDelco D585 'Round' Style) — expected: ~0.820 ohms. Failure: A reading significantly higher or lower than the specification, or an open circuit (infinite resistance).
• Ignition Coil Secondary Resistance (ACDelco D585 'Round' Style) — expected: ~7.10k ohms. Failure: A reading significantly outside the specification.
• Spark Plug Wire Resistance — expected: Under 50 ohms per foot of length.. Failure: Excessively high resistance or an open circuit indicates a bad wire.

Hidden / Shadow Codes Worth Checking

• Misfire Counters (Current/History): These are not discrete codes but live data PIDs showing the number of misfire events per cylinder. While a few random counts can be normal from road vibrations, a rapidly increasing counter for cylinder 3 confirms a persistent misfire that needs diagnosis. (see via A GM Tech2, GDS2, or a high-end professional scan tool with GM-specific software is required to view the misfire counters.)

Scan Tool Commands That Help

• GM Tech2 / GDS2: Misfire Graphic / Misfire Data List — Use this to monitor the live misfire counters for each cylinder to confirm the misfire is isolated to cylinder 3 and to see if it's a constant or intermittent issue.
• GM Tech2 / GDS2: Special Functions > Crankshaft Variation Learn (CASE Learn) — This procedure should be performed after replacing a crankshaft position sensor or on high-mileage engines to recalibrate the sensor's readings. It can improve the accuracy of misfire detection and reduce false misfire counts.

Wiring & Ground Locations

• G102 — On the left rear of the engine block/cylinder head.. This is the primary ground point for all eight ignition coils. A loose or corroded connection at G102 can cause a weak or intermittent spark on any cylinder, including cylinder 3, leading to a misfire that is difficult to diagnose by swapping parts alone.
• Cylinder 3 Fuel Injector Wire — In the engine harness leading to the fuel injector on cylinder 3.. For electrical testing, the high voltage supply wire to the cylinder 3 injector is typically Light Green/White (L-GN/WH). This allows a technician to perform voltage and continuity checks on the correct wire.
• G103 — At the rear of the left-hand (driver's side) engine head.. While G102 is the direct ground for the coils, G103 is a major engine and chassis ground. A poor connection here can cause various unpredictable electrical issues, including problems with the ECM or other sensors that could indirectly contribute to a misfire code.

Real Owner Repair Stories

• GMTNation forum user (2007 GM Vehicle (Trailblazer)) — No DTCs initially, but suspected a misfire.
  ❌ Tried (didn't work) Initial visual inspection showed nothing.
  ✅ What actually fixed it Used Tech2Win software to view the misfire graphics, which identified a problem on cylinder #4. Upon removing the ignition coil, it was found to be drenched in oil from a leaking valve cover gasket. The oil shorted out the coil. Replacing the valve cover gasket and the compromised coil pack resolved the issue.

"I Checked Everything" — The Actual Cause

• In cases involving the 5.3L engine, a technician may find that the ignition system (plugs, wires, coils) and fuel system (injector, pressure) are all functioning perfectly, yet the P0303 code persists. The root cause is often a purely mechanical failure of the Active Fuel Management (AFM) lifter for cylinder 3. A collapsed or stuck lifter results in a loss of compression for that cylinder, causing a misfire that ignition or fuel system tests will not identify.

OEM Part Supersession History

• ACDelco D585 (or compatible) → N/A — N/A
  Heads up: These engines use a 'round' or 'Delphi' style ignition coil (like the D585). Be aware that other GM trucks from a similar era used a 'square' or 'Melco' style coil (like the D581). The two are not interchangeable as the mounting bracket and connector are different. Ensure you are purchasing the correct round style for the 2010-2013 Savana.

Model Year Variations Within This Range

• 2010-2013: The most significant variation is engine-dependent, not year-dependent. The 5.3L V8 (RPO code LC9) is equipped with Active Fuel Management (AFM). The 4.8L V8 (LY2) and 6.0L V8 (LY6/L96) in this van do not have AFM. Therefore, the common and severe issue of AFM lifter failure as a cause for P0303 is specific to the 5.3L engine option.