P0352 on 2007-2010 Hummer H3 3.7L: Ignition Coil 'B' Circuit Failure Causes and Fixes

What's Unique About the 2007-2010 Hummer H3

The 3.7L inline-five (I5) engine in the Hummer H3 uses a coil-on-plug ignition system, which is generally reliable. However, these engines are known to be susceptible to heat degradation, which can cause the epoxy in the factory ignition coils to break down over time, leading to failure. While not directly related to a P0352 code for cylinder #2, it's worth noting a known issue on the I5 engine where water can leak past the hood clips or from clogged sunroof drains and pool in the rearmost spark plug well (cylinder #5), causing rust and misfires there. This highlights a potential vulnerability in the coil-on-plug design to moisture.

Symptoms You May Notice

• Check Engine Light is on
• Flashing Check Engine Light (if the misfire is severe)
• Rough or shaky idle
• Engine misfire, which may feel like a stumble or hesitation during acceleration
• Reduced engine power and responsiveness
• Difficulty starting the engine

Most Likely Causes

1. Faulty Ignition Coil on Cylinder #2 🔴 High Probability The factory ignition coils on the 3.7L LLR engine are known to be susceptible to thermal degradation over time, causing the coil's internal components to fail.
   How to confirm: Swap the ignition coil from cylinder #2 with another cylinder (e.g., cylinder #1 or #3). Clear the codes and drive the vehicle. If the code changes to P0351 or P0353 respectively, the coil is faulty. This is the most common and effective diagnostic step.
   Typical fix: Replace the faulty ignition coil. It is often recommended to replace all five coils and spark plugs at the same time for preventative maintenance.
   Est. part cost: $30-$70 per coil
2. Worn or Fouled Spark Plug in Cylinder #2 🟡 Medium Probability
   How to confirm: Remove the spark plug from cylinder #2 and inspect it. Look for signs of excessive wear on the electrode, carbon fouling, oil, or coolant contamination. A healthy spark plug should have a light tan color. The correct gap for the OEM plug is 0.043 inches.
   Typical fix: Replace the spark plug. It is best practice to replace all five spark plugs at the same time. 🎬 See how to replace both coils and spark plugs Use high-quality Iridium plugs like the OEM-spec ACDelco 41-103 for best performance.
   Est. part cost: $8-$15 per plug
3. Damaged Wiring or Connector for Coil #2 ⚪ Low Probability The wiring harness in the engine bay is exposed to heat and vibration, which can cause wires to break internally or the plastic connector to become brittle and fail over time.
   How to confirm: Visually inspect the wiring harness and connector going to the ignition coil on cylinder #2. Look for any signs of melting, corrosion, chafing, or loose pins. With the engine running, carefully wiggle the connector and wiring to see if it affects the idle, which would indicate a poor connection. Use a multimeter to check for proper voltage and ground at the connector.
   Typical fix: Repair the damaged section of wiring or replace the pigtail connector. Common replacement part numbers include ACDelco PT2183 and GM 15306431.
   Est. part cost: $15-$30 for a new connector

Rare But Worth Checking

• Faulty Powertrain Control Module (PCM): This is very rare. The PCM's internal driver for the ignition coil can fail, but all other potential causes should be exhaustively ruled out before considering PCM replacement.

Diagnosis Steps

1. Retrieve the stored trouble codes using an OBD-II scanner to confirm P0352 is present.
2. Locate cylinder #2, which is the second ignition coil from the front of the engine.
3. Visually inspect the ignition coil, wiring, and connector for cylinder #2 for any obvious damage, melting, or corrosion.
4. To confirm a bad coil, swap the ignition coil from cylinder #2 with an adjacent coil (e.g., cylinder #1). The coils are held down by a single 10mm bolt.
🎬 Watch: Step-by-step guide to replacing your H3 ignition coils
5. Clear the trouble codes with the scanner.
6. Start the engine and let it run for a few minutes. Re-scan for codes.
7. If the code has changed to P0351 ('Ignition Coil A Circuit Malfunction'), the ignition coil is confirmed to be faulty and needs replacement.
8. If the P0352 code returns, the problem is likely with the spark plug or the wiring circuit.
9. Remove and inspect the spark plug from cylinder #2. Replace if it is worn, fouled, or damaged. Ensure the new plug is gapped to 0.043".
10. If the coil and spark plug are good, test the wiring circuit for cylinder #2. Check for 12v power and a proper ground signal from the PCM using a multimeter and wiring diagram. Wiggle the harness while testing to check for intermittent breaks.

Parts You'll Likely Need

• Ignition Coil (OEM #19421261) — This is the most frequent failure point for a P0352 code on the Hummer H3. The OEM part number 19421261 supersedes older numbers like 12629472.
  Trusted brands: ACDelco (OEM), Delphi, Denso, NGK
  OEM price range: $50-$70
  Aftermarket price range: $30-$50
• Spark Plug (OEM #41-103) — A worn or fouled spark plug can cause ignition issues and should be replaced if its condition is poor, especially if the ignition coil is being replaced. The correct gap is 0.043 inches.
  Trusted brands: ACDelco (OEM), NGK
  OEM price range: $10-$15
  Aftermarket price range: $8-$12
• Ignition Coil Connector (OEM #15306431) — The plastic connector can become brittle from heat cycles and break, or the terminals can corrode, causing a poor connection to the coil.
  Trusted brands: ACDelco (PT1496), Dorman (645-940)
  OEM price range: $20-$30
  Aftermarket price range: $10-$20

Related Codes That Often Appear With This One

• P0302 — P0302 is a 'Cylinder 2 Misfire Detected' code. Since P0352 indicates a fault in the ignition circuit for cylinder 2 🎬 Watch: Understanding the causes and fixes for code P0352, a misfire in that same cylinder is a direct consequence.
• P0300 — If the ignition issue is intermittent or other coils are also failing, a 'Random Misfire Detected' code (P0300) might appear alongside the more specific P0352.

Platform-Specific Known Issues

• Water Intrusion in Spark Plug Wells: A known issue on the H3 platform involves water leaking past hood clips or from clogged sunroof drains, which can pool in the spark plug wells. While most commonly reported for cylinder #5 (the rearmost cylinder), it can potentially affect other cylinders and lead to rusted coils and plugs, causing misfires.

Mechanic-Grade Diagnostic Values

• Ignition Coil Primary Resistance — expected: 0.4 to 2.0 Ohms. Failure: A reading of 0 Ohms indicates a shorted coil, while an infinite (OL) reading indicates an open circuit.
• Ignition Coil Secondary Resistance — expected: 3,800 to 15,000 Ohms (3.8kΩ - 15kΩ). Failure: A reading significantly outside this range indicates an internal failure of the coil's secondary winding.
• Ignition Coil Connector Power (Key On, Engine Off) — expected: 10 to 12 Volts DC. Failure: No voltage, or voltage significantly below 10V, indicates a problem with the power supply wiring or the ignition fuse/relay upstream of the coil.

Hidden / Shadow Codes Worth Checking

• Historical Misfire Counters: This is not a specific trouble code, but rather a data parameter. It shows the exact number of misfire events logged for each individual cylinder over a drive cycle, even if the misfire count isn't high enough to set a specific P030x code. This data is extremely useful for identifying an intermittently failing coil or wiring issue before it becomes a hard fault. (see via A professional-grade scan tool, such as a GM Tech2 or equivalent, is required to access this level of historical data from the PCM.)

Scan Tool Commands That Help

• GM Tech2 / GDS2 or equivalent: Module Test / Output Control for Ignition Coil Driver — This function is used when a new coil and spark plug do not resolve the P0352 code. A technician can command the PCM to pulse the driver for cylinder #2. Using a noid light or oscilloscope on the signal wire at the coil connector, the technician can verify if the PCM is actually sending the command to fire. If the command is sent but the tool shows no signal, it confirms the PCM's internal driver has failed.

Wiring & Ground Locations

• Engine Control Module (ECM/PCM) — Located in the right rear corner of the engine compartment.. The ECM contains the driver circuit that sends the signal to fire the #2 ignition coil. All wiring for the coil originates from this module.
• G103 — On the lower left side of the engine block.. This is a primary engine ground. A loose or corroded connection here can cause unstable voltage and erratic signals throughout the ignition system, potentially leading to misfires or circuit codes like P0352.
• Ignition Coil Harness — Runs across the top of the engine's camshaft cover to each of the five ignition coils.. This harness is exposed to significant heat. Wires can become brittle and crack, or chafe against the engine, causing a short or open circuit specifically for the cylinder #2 coil.

Real Owner Repair Stories

• Technician analysis of similar P035x failures on Ford/Mazda platforms (Various vehicles with coil-on-plug systems) — Persistent P035x code (e.g., P0352) even after replacing the ignition coil and spark plug for the specified cylinder.
  ❌ Tried (didn't work) Replacing the ignition coil for the affected cylinder, sometimes multiple times., Replacing the spark plug.
  ✅ What actually fixed it The root cause was a failed ignition coil driver inside the Powertrain Control Module (PCM). The original ignition coil had failed and shorted internally, sending a voltage spike back to the PCM and destroying the delicate driver circuit for that specific cylinder. The final repair required replacing the PCM and all ignition coils to prevent the new PCM from being damaged by another old, failing coil.

OEM Part Supersession History

• 12596547, 12612369, 12629472 → 19421261 — Standard part evolution for GM's Atlas engine family, likely for improved durability, heat resistance, or manufacturing consistency.

Model Year Variations Within This Range

• 2007 vs 2008-2010: There were changes to the control module architecture around the 2008 model year. Some earlier models used a single Powertrain Control Module (PCM) that managed both engine and transmission functions. Later models may have used a separate Engine Control Module (ECM) and Transmission Control Module (TCM). While this doesn't change the fundamental cause of a P0352, it's important for sourcing a replacement control module if one is needed, as they are not interchangeable between these configurations.

Diagnostic Flowchart

Other Known Issues on This Vehicle

Issues unrelated to this code that are worth knowing about as an owner of this generation:

• Cracked Exhaust Manifold 🔴 High — Very common, especially over 75,000 miles. The original cast iron manifold is prone to cracking from heat cycles, often causing a ticking noise when cold and triggering P0420 codes.
• GM Passlock II Anti-Theft System Failure 🟠 Medium — A widespread and frustrating issue where the Passlock sensor in the ignition lock cylinder fails, causing a no-start or start-and-stall condition with a flashing security light.
• Electronic Throttle Body Failure 🟠 Medium — The throttle body can fail or become excessively dirty, leading to a 'Reduced Engine Power' message, unstable idle, and codes like P2135 or P2101.
• Clogged Sunroof Drains 🟡 Low — The sunroof drain tubes are known to clog easily, causing water to leak into the cabin, typically onto the passenger floorboard or from the overhead console.
• Premature Valve Seat Wear (Early Models) 🔴 High — More common on the 2006 3.5L but still a concern for early 3.7L engines, this cylinder head issue causes loss of compression and persistent misfires (e.g., P0300, P0305) that are not fixable with a tune-up. (Ref: GM TSB #PIP4013D)
• Broken MAP Sensor Wiring 🟠 Medium — Wires for the MAP sensor can break internally near the connector, causing rough running, stalling, and codes like P0107 without any visible damage to the harness. (Ref: GM TSB #PIP4409F)

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: For this specific repair, buying a used ignition coil is generally not recommended. The OEM coils are known to fail from heat degradation over time, so a used part from a junkyard likely has significant wear and a short remaining lifespan. A used wiring harness connector (pigtail) is a viable option if the plastic is not brittle and the wires are in good condition.

Donor-vehicle mileage cap: roughly under 80000 miles for the part to have meaningful remaining life.

What to inspect on the donor part:

• For a connector pigtail, inspect for any cracks in the plastic housing.
• Ensure the locking tab on the connector is intact and functional.
• Check for any signs of corrosion (green or white powder) on the metal pins inside the connector.
• Ensure there are at least 4-6 inches of clean, un-spliced wire attached.

OEM-only on this vehicle (don't cheap out):

• Powertrain Control Module (PCM) - While used PCMs are available, they require professional programming to the vehicle's VIN. For reliability, a new or professionally remanufactured and programmed unit is strongly advised.

Aftermarket brands forum-validated for this vehicle:

• ACDelco (OEM)
• Delphi
• NGK
• Denso

Brands owners have reported issues with on this vehicle:

• Unbranded, 'white-box' ignition coils from online marketplaces. These often use lower-quality windings and epoxy, leading to premature failure and potentially damaging the PCM.

Real Owner Stories

Aggregated from forums and TSBs cited above. Mileages and costs reflect what owners reported in those sources.

Related OBD-II Codes

• P0302 — Cylinder 2 Misfire Detected; often accompanies P0352 when the ignition coil circuit fault is severe enough to cause a dead misfire.
• P0351 — Ignition Coil A (Cylinder 1) Circuit Malfunction; used during diagnostics to confirm a faulty coil by swapping the coil from cylinder 2 to cylinder 1.
• P0353 — Ignition Coil C (Cylinder 3) Circuit Malfunction; used during diagnostics to confirm a faulty coil by swapping the coil from cylinder 2 to cylinder 3.
• P0300 — Random or Multiple Cylinder Misfire; can occur alongside P0352 if multiple coils are suffering from thermal degradation or if there is a cylinder head issue per TSB #PIP4013D.
• P0107 — MAP Sensor Circuit Low; related to the H3's known issue of broken MAP sensor wiring (TSB #PIP4409F) which causes similar rough running symptoms.
• P2135 — Throttle/Pedal Position Sensor/Switch Voltage Correlation; related to the H3's known electronic throttle body failure mode.
• P0420 — Catalyst System Efficiency Below Threshold; often triggered by the cracked exhaust manifold common on the 3.7L engine.

Frequently Asked Questions