P0305 on 2016 Acura MDX: Cylinder 5 Misfire Causes and Fixes

What's Unique About the 2016-2016 Acura MDX

The 2016 MDX uses the J35Y5 engine, a direct-injection 3.5L V6 featuring Variable Cylinder Management (VCM). While generally reliable, the most common cause for a single-cylinder misfire like P0305 is a simple ignition coil or spark plug failure. However, this direct-injection engine is also known for potential fuel injector issues, as documented in multiple Acura TSBs requesting parts for investigation. Cylinder 5 is located on the front bank of the engine (closest to the radiator), making the ignition coil and spark plug easily accessible for diagnosis and repair.

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 vibrating idle
• Hesitation or stumbling during acceleration
• Noticeable loss of engine power
• Solid or flashing Check Engine Light
• Potential fuel smell from the exhaust
• Engine runs fine when cold, but starts to misfire and idle roughly once it warms up

Most Likely Causes

1. Faulty Ignition Coil 🔴 High Probability → Shop Ignition Coil Ignition coils are a common wear-and-tear item that can fail with age and heat cycles. Failure of a single coil is a frequent cause for isolated misfire codes on J-series engines.
   How to confirm: Swap the ignition coil from cylinder 5 with an adjacent one (e.g., cylinder 4 or 6). Clear the codes and drive the vehicle. If the misfire code changes to P0304 or P0306, the ignition coil is faulty.
   Typical fix: Replace the failed ignition coil. It is often recommended to replace all coils on the same bank, or all six, if they are original and have high mileage.
   Est. part cost: $60 - $90
2. Worn or Fouled Spark Plug 🔴 High Probability → Shop Spark Plug Spark plugs have a finite service life. An old plug with a worn electrode or one fouled by oil or carbon deposits can fail to produce a strong enough spark. Some owners report spark plugs on J-series engines can loosen over time, leading to misfires.
   How to confirm: After confirming the coil is good, remove the spark plug from cylinder 5. Inspect it for wear, carbon buildup, oil fouling, or damage to the insulator. Check that it was properly torqued. Compare it to a new plug. 🎬 Watch: How to remove and replace your MDX spark plugs.
   Typical fix: Replace the spark plug in cylinder 5. It is best practice to replace all six spark plugs at the same time with the recommended NGK or Denso iridium plugs to ensure even performance.
   Est. part cost: $15 - $45 per plug
3. Faulty Fuel Injector 🟡 Medium Probability → Shop Fuel Injector The J35Y5 engine uses direct injection. Acura and Honda have issued multiple Technical Service Bulletins (TSBs) for this engine family (including platform mates like the Honda Pilot) related to misfires caused by clogged or faulty fuel injectors. Debris from the high-pressure fuel pump or the injector manufacturing process can cause them to fail.
   How to confirm: This is more complex to diagnose. It involves listening for the injector's clicking sound with a mechanic's stethoscope or testing its resistance and signal. A professional diagnosis may be required. Swapping injectors is possible but much more labor-intensive than swapping coils.
   Typical fix: Replace the faulty fuel injector. Due to the known issues, some shops recommend replacing all injectors on the affected bank or all six at once. Acura sells a kit of 6 injectors for this purpose. 🎬 See this walkthrough on replacing fuel injectors to fix misfires.
   Est. part cost: $100 - $200 per injector, but often sold as a set which can be over $1,200.

Rare But Worth Checking

• Low Engine Oil Level / VCM Issues: Some owners on forums have noted that Honda/Acura J-series engines can consume oil. Low oil levels can affect the VCM (Variable Cylinder Management) system, which deactivates cylinders (including the front bank 4-5-6) to save fuel. VCM operation can sometimes lead to spark plug fouling on the affected cylinders, causing misfires. Always check the oil level first.
• Intake Valve Carbon Buildup: As a direct-injection engine, the intake valves are not cleaned by fuel spray. Over time, carbon can build up and restrict airflow into the cylinder, causing a misfire. This typically requires professional cleaning (e.g., walnut blasting).
• Mechanical Engine Issue: Though uncommon, a persistent P0305 after checking ignition and fuel components could point to a mechanical problem like low compression from a bad valve or worn piston rings. A compression test would be needed to confirm this.

Diagnosis Steps

1. Read the code with an OBD-II scanner to confirm P0305 is present.
2. Check the engine oil level and top off if necessary, as low oil can affect VCM operation.
3. Identify cylinder 5. On the 2016 MDX 3.5L V6, it is the middle cylinder on the front bank (closest to the radiator). The front bank is cylinders 4-5-6 from passenger to driver side.
4. Swap the ignition coil from cylinder 5 with the coil from cylinder 4 (the one to its right when facing the engine).
5. Clear the fault codes with the scanner and start the engine. Let it idle and rev it gently to see if the Check Engine Light returns.
6. Re-scan for codes. If the code is now P0304, the ignition coil you moved is bad and needs to be replaced.
7. If the code remains P0305, the coil is likely good. Move the coil back to its original position.
8. Repeat the swap process with the spark plug from cylinder 5 and cylinder 4. If the code moves to P0304, the spark plug is the culprit.
9. If the code still remains P0305 after swapping the coil and plug, the issue is likely with the fuel injector or a mechanical problem. Given the known injector issues, this is the next logical step. Further professional diagnosis is recommended due to the complexity of injector replacement.

Parts You'll Likely Need

• Ignition Coil (OEM #30520-5G0-A01) — This is the most common failure part for a single-cylinder misfire on this engine.
  Trusted brands: Denso (OEM supplier), NGK, Delphi
  OEM price range: $85 - $110
  Aftermarket price range: $60 - $90
• Spark Plug (OEM #12290-R9P-A01) — A worn or fouled spark plug is the second most likely cause. It is a routine maintenance item that should be replaced at specified intervals.
  Trusted brands: NGK (DILZKR7B11G), Denso
  OEM price range: $40 - $55
  Aftermarket price range: $15 - $30
• Fuel Injector Set (OEM #16010-R9P-305) — Faulty fuel injectors are a known issue on this platform, as noted in Acura TSBs. They are often the culprit if coils and plugs are good.
  Trusted brands: Acura (OEM)
  OEM price range: $1600 - $1800 for a set of 6
  Aftermarket price range: Not Recommended

Related Codes That Often Appear With This One

• P0300 — If the misfire becomes more widespread or random, a P0300 (Random/Multiple Cylinder Misfire) code may appear alongside P0305.
• P0301, P0302, P0303, P0304, P0306 — If other cylinders are also misfiring, their corresponding codes will be stored. Seeing multiple codes may point towards a systemic issue like a faulty fuel injector set or carbon buildup rather than a single component failure.
• P0420 / P0430 — If a misfire is left unresolved for too long, unburnt fuel will damage the catalytic converter, triggering a P0420 (Bank 1) or P0430 (Bank 2) code.

Technical Service Bulletins (TSBs) & Recalls

• BPAS04242017901: Mentions P0305 in a list of misfire codes under investigation by Acura for the 2016 MDX.
• BTI&08252021901: Follow-up TSB for 2016-2020 models requesting collection of fuel injectors and high-pressure fuel pumps to investigate misfire causes.

Platform-Specific Known Issues

• A Technical Service Bulletin (TSB), #BPAS04242017901, was issued for the 2016 MDX mentioning P030x codes, including P0305. The bulletin was for the purpose of information gathering by the manufacturer to understand the cause of misfire conditions, but does not list a specific repair.
• Acura later issued TSB #BTI&08252021901 for 2017-2020 models to collect parts, specifically noting the issue had been 'traced to the fuel injectors'.
• Honda TSB 18-025 for platform-mate vehicles with the same engine family (J35Y6) states that debris from the high-pressure pump or injector machining process can cause internal wear or clogging, leading to misfires.

Mechanic-Grade Diagnostic Values

• Ignition Coil Primary Winding Resistance — expected: 0.49 - 0.57 Ω. Failure: A reading outside of this range indicates a faulty coil.
• Ignition Coil Secondary Winding Resistance — expected: 9.5 - 11.1 kΩ. Failure: A reading outside of this range indicates a faulty coil.
• Low-Pressure Fuel System Pressure (at key-on, engine-off) — expected: Approx. 40 - 60 psi. Failure: Significantly lower pressure indicates a weak in-tank fuel pump, which could contribute to misfires under load.

Hidden / Shadow Codes Worth Checking

• Mode $06, Monitor ID $A6: This is not a DTC, but a specific monitor ID within the OBD-II system's Mode $06 data. Monitor IDs $A2 through $A7 correspond to the raw misfire counters for cylinders 1 through 6, respectively. For P0305, a technician would check Monitor ID $A6 to see the number of misfire events counted on cylinder 5, even if the count is not yet high enough to trigger the check engine light. (see via An advanced OBD-II scanner capable of displaying Mode $06 data.)

Scan Tool Commands That Help

• Acura i-HDS (or compatible advanced scanner): CKP Pattern Clear / Learn Procedure — This procedure is critical after the battery has been disconnected for an extended period, or after replacing major components like the timing belt or fuel pump. The PCM can lose its learned crankshaft position sensor pattern, leading to false misfire codes even when no mechanical fault exists.
• Acura i-HDS (or compatible advanced scanner): Misfire Cylinder Test / Power Balance Test — This function helps isolate a problematic cylinder by sequentially cutting fuel or spark to each one and measuring the corresponding drop in engine RPM. The cylinder that causes the least amount of RPM drop when disabled is the one contributing the least power, and is likely the source of the misfire.
• Acura HDS / i-HDS: DATA LIST - CYL5 MISFIRE — During diagnosis, a technician can use the factory scan tool to watch a live counter of misfire events specifically for cylinder 5. This allows for real-time monitoring during idle and test drives to see the exact conditions under which the misfire occurs.

Real Owner Repair Stories

• Reddit user, r/AskMechanics (2012 Acura MDX (126k miles) - Note: Older generation but demonstrates a key J-series engine issue.) — Engine misfiring with code P0306 (Cylinder 6 Misfire) immediately after a timing belt replacement and having the battery disconnected for 8 days.
  ❌ Tried (didn't work) Swapping ignition coil from cylinder 6 to cylinder 5., Swapping spark plug from cylinder 6 to cylinder 4.
  ✅ What actually fixed it The user was advised by others that the problem was not a faulty part, but that the ECU needed a 'Crank Pattern Calibration / Crank Pattern Relearn' procedure performed with a professional scan tool (like an Autel MaxiSYS) because the learned values were lost when the battery was disconnected for an extended period.
• YouTube channel 'Misfire P0305 Rough Idle Acura Check Engine Light Code Car Shaking' (Acura (model not specified, but J-series V6)) — P0305 check engine light code, rough idle, car shaking.
  ❌ Tried (didn't work) The video focuses directly on the final repair, implying prior diagnosis pointed away from spark/ignition.
  ✅ What actually fixed it The creator replaced the three fuel injectors on the front bank of the engine, which includes cylinder 5. Although only cylinder 5 was confirmed bad, all three on the shared fuel rail were replaced as a preventative measure due to age.
• YouTube channel 'JNB Tuning' (Acura MDX (3rd Gen)) — P0304 (Cylinder 4 Misfire), but diagnostic process is relevant for any single cylinder misfire on this platform.
  ❌ Tried (didn't work) Replacing all spark plugs., Swapping ignition coils (the misfire did not move)., Performing a compression test (all cylinders were good)., Inspecting the cylinder with a borescope (no visible issues).
  ✅ What actually fixed it The issue was suspected to be a partially clogged fuel injector. After all mechanical and ignition checks passed, the owner added a quality fuel system cleaner and switched to a different brand of top-tier gasoline. The misfire did not return after a month of driving, suggesting the injector was the likely culprit. The creator also noted that a valve adjustment is another common cause for misfires on this engine that is often overlooked.

"I Checked Everything" — The Actual Cause

• In cases where spark plugs, ignition coils, and fuel injectors all check out, and there are no vacuum leaks, a persistent P0305 can be caused by the PCM losing its crankshaft position sensor (CKP) calibration. This often happens after a battery has been disconnected for a long time or after major engine work. The fix is not a part replacement, but a 'CKP Pattern Relearn' procedure using a dealer-level scan tool.

OEM Part Supersession History

• 17045-TZ5-A00 → 17045-TZ5-A10 — Part update/revision for the low-pressure fuel pump module assembly.