P0356 on 2008-2009 Ford Taurus 3.5L: Ignition Coil 'F' Circuit Malfunction Causes and Fixes

What's Unique About the 2008-2009 Ford Taurus

On this specific generation of Ford vehicles with the 3.5L V6, a failed ignition coil can short out and send a voltage spike back to the Powertrain Control Module (PCM), damaging the internal driver circuit for that coil. This is a well-documented weakness. Ford issued a Technical Service Bulletin (TSB 13-4-17) acknowledging that a physically damaged coil-on-plug (e.g., cracked housing) can lead to PCM failure on 2008 Taurus models built before March 1, 2008. Because of this, it's not just a matter of replacing the coil; it's crucial to determine if the coil failure also damaged the PCM, as a damaged PCM will destroy a new coil instantly.

Symptoms You May Notice

• Rough idle or engine shaking
• Flashing or solid check engine light
• Noticeable loss of power and poor acceleration
• Hesitation when trying to accelerate
• Reduced fuel economy
• Smell of unburnt gasoline from the exhaust

Most Likely Causes

1. Failed Ignition Coil on Cylinder #6 🔴 High Probability → Shop Ignition Coil The original Motorcraft coils on this engine are a known failure point. Heat and vibration cause the internal windings to fail over time, leading to cracks in the housing which can cause a short.
   How to confirm: Swap the ignition coil from cylinder #6 with an adjacent cylinder (e.g., cylinder #5). Clear the codes. If the code changes to P0355, the coil is bad. Cylinder #6 is on the front bank (radiator side), closest to the driver's side, making it the easiest to access.
   Typical fix: Replace the faulty ignition coil. It is often recommended to replace the corresponding spark plug at the same time. Many owners choose to replace all six coils and plugs if they are original, to prevent future failures, though only the front bank is easily accessible. 🎬 See this step-by-step spark plug and coil replacement walkthrough
   Est. part cost: $40-$80
2. Damaged Wiring or Connector 🟡 Medium Probability The plastic connector for the ignition coil can become brittle from engine heat cycles and break. The wiring can also chafe or corrode, causing an open or short in the circuit. In some Ford engine configurations, an open circuit in the coil-on-plug connector for cylinder 6 can occur due to interference with engine components like the intake air expansion resonator, as noted in TSB Bulletin #TSB18-2047.
   How to confirm: After ruling out the coil itself, visually inspect the wiring harness and connector for cylinder #6. Look for cracked plastic, corroded pins, or wires that are frayed or melted. Check for a solid connection and that the locking tab isn't broken.
   Typical fix: Repair the damaged section of wire or replace the pigtail connector. A common pigtail replacement is Motorcraft WPT-931.
   Est. part cost: $15-$30
3. Worn or Fouled Spark Plug 🟡 Medium Probability → Shop Spark Plug A spark plug with an excessive gap or heavy carbon fouling can put extra strain on the ignition coil, causing it to overheat and fail prematurely. The recommended service interval for spark plugs is typically around 100,000 miles.
   How to confirm: When you remove the ignition coil, remove the spark plug and inspect it. Look for a worn electrode, cracks in the ceramic, or heavy deposits. The correct spark plug gap is critical for proper function.
   Typical fix: Replace the spark plug. It's best practice to replace all six spark plugs if they are near the end of their service life.
   Est. part cost: $8-$20 per plug

Rare But Worth Checking

• Failed Powertrain Control Module (PCM): → Shop Engine Control Module (ECM) While rare on its own, a failed ignition coil on this platform has a higher-than-average chance of damaging the PCM's coil driver circuit. If a new coil and good wiring do not fix the P0356 code (or the code returns immediately), the PCM is the likely culprit. Ford TSB 13-4-17 outlines a diagnostic path that leads to PCM replacement if a physically damaged coil is found. Furthermore, NHTSA ODI #10444492 suggests that PCM and coil primary circuit faults (P0351-P0356) may sometimes be linked to radio frequency interference. Companies like Circuit Board Medics specialize in repairing these specific PCM failures, which can be a cost-effective alternative to a new unit from the dealer.

Diagnosis Steps

1. Read the code with an OBD-II scanner to confirm P0356 is present. Note any other codes, especially P0306 or other P035x codes.
2. Locate cylinder #6. On the transverse 3.5L V6 in the Taurus, the cylinders against the firewall are Bank 1 (1-2-3, passenger to driver) and the cylinders by the radiator are Bank 2 (4-5-6, passenger to driver). Cylinder #6 is on the radiator side, closest to the driver's side.
3. Swap the coil from cylinder #6 with the coil from cylinder #5 (the middle coil on the front bank).
4. Clear the trouble codes with the scanner.
5. Start the engine and let it run for a few minutes. Rescan for codes.
6. If the code is now P0355 ('Ignition Coil E'), the ignition coil you moved is faulty and needs to be replaced.
7. If the code P0356 returns, the problem lies in the wiring or the PCM. Visually inspect the connector and wiring to cylinder #6 for any visible damage, corrosion, or loose pins.
8. If the wiring appears intact, inspect all ignition coils for physical damage like cracks or burn marks. If any are found, especially on a 2008 model, TSB 13-4-17 indicates the PCM is likely damaged.
9. For advanced diagnosis, use a noid light on the cylinder #6 connector. When cranking the engine, the light should flash, indicating the PCM is sending a trigger signal. If it does not flash (and the wiring is good), the PCM driver for that cylinder is dead.
10. If the PCM is suspected, the official Ford procedure is to replace the PCM, all six ignition coils, and all six spark plugs to prevent a repeat failure.

Parts You'll Likely Need

• Ignition Coil (OEM #DG520 (Motorcraft)) — This is the most common failure item for a P0356 code. The original equipment coils are known to fail. Using genuine Motorcraft parts is highly recommended to avoid premature failure, as many owners report issues with counterfeit or cheap aftermarket parts.
  Trusted brands: Motorcraft, NGK, Denso, Carquest Premium
  OEM price range: $70-$90
  Aftermarket price range: $40-$75
• Spark Plug (OEM #SP537 (Motorcraft Finewire Platinum)) — It is best practice to replace the spark plug when replacing an ignition coil, especially if the plugs are high-mileage. A worn plug can cause the new coil to fail prematurely. Plugs should be gapped correctly before installation.
  Trusted brands: Motorcraft, NGK, Autolite
  OEM price range: $10-$15
  Aftermarket price range: $8-$12
• Powertrain Control Module (PCM) (OEM #8U7Z-12A650-B (Varies by calibration, check with VIN)) — Required if the original PCM was damaged by a shorted ignition coil, as is common on this platform per TSB 13-4-17. Must be replaced along with all coils and plugs.
  Trusted brands: Ford (New or Remanufactured), Circuit Board Medics (Repair Service)
  OEM price range: $800-$1200
  Aftermarket price range: $250-$400 (for repair service)

Related Codes That Often Appear With This One

• P0306 — P0306 means 'Cylinder 6 Misfire Detected'. P0356 is the specific electrical circuit fault that prevents the coil from firing, which in turn causes the misfire. These codes almost always appear together.
🎬 Watch: How to diagnose and fix a Cylinder 6 misfire
• P0351, P0352, P0353, P0354, P0355 — If you see multiple P035x codes along with P0356, this is a very strong indicator that the PCM has failed and is no longer able to control multiple coil circuits. This scenario almost always requires replacing the PCM, all six coils, and all six plugs.

Technical Service Bulletins (TSBs) & Recalls

• TSB 13-4-17: MIL ON WITH DTCS - P0351, P0352, P0353, P0354, P0355, AND/OR P0356 - BUILT ON OR BEFORE 3/1/2008.
• TSB Bulletin #TSB18-2047: Addresses illuminated MIL with DTC P0355 and/or P0356, which may be due to an open circuit in the coil-on-plug connectors for cylinders 5 and/or 6.

Platform-Specific Known Issues

• Ford Technical Service Bulletin (TSB) 13-4-17 (which supersedes earlier versions) was issued for 2008 Taurus models built on or before 3/1/2008. It addresses P035x codes caused by a damaged coil-on-plug. The official service procedure, if a physically damaged coil is found, is to replace the PCM, all six coils, and all six spark plugs. This is to prevent the faulty PCM from immediately destroying the new parts.

Mechanic-Grade Diagnostic Values

• Ignition Coil Primary Winding Resistance — expected: 0.4 to 2.0 ohms (typical). A Motorcraft DG511 (similar platform) specifies 0.55 ohms.. Failure: A reading of infinite ohms (OL) indicates an open circuit. A reading of zero ohms indicates a short. Any reading significantly outside the expected range suggests a faulty coil.
• Ignition Coil Secondary Winding Resistance — expected: 6,000 to 10,000 ohms (6kΩ to 10kΩ). A Motorcraft DG511 (similar platform) specifies 5,500 ohms (5.5kΩ).. Failure: A reading of infinite ohms (OL) indicates an open secondary winding. A reading far outside the specification suggests internal failure.
• Ignition Coil Connector - Power Supply Voltage — expected: ~12 Volts (Battery Voltage) with Key On, Engine Off.. Failure: Significantly less than 12V or no voltage indicates a problem with the power supply wire or the ignition coil fuse/relay.
• Ignition Coil Connector - PCM Trigger Signal — expected: A pulsing ground signal when the engine is cranking or running. This is best observed with a noid light (which should flash) or an oscilloscope.. Failure: No flashing light or no signal from the PCM indicates a wiring issue or a failed PCM driver circuit.

Scan Tool Commands That Help

• Ford IDS (Integrated Diagnostic Software): Power Balance Test — This is a critical function for diagnosing misfires on Ford vehicles. It displays a histogram showing the relative power contribution of each cylinder. A cylinder with a P0356 fault will show a significant drop in contribution, confirming the misfire location without needing to swap parts.
• Ford IDS (Integrated Diagnostic Software): Coil-On-Plug Stress Test — This is a specific self-test function that commands the coils to fire and monitors the circuit response. It can help identify intermittent faults in the coil, wiring, or PCM driver that may not be present at idle.
• Ford IDS (Integrated Diagnostic Software): Retrieve Continuous Memory DTCs — This function is used to read codes that are stored but may not be active or illuminating the MIL. It can reveal a history of faults that helps diagnose intermittent problems.

Wiring & Ground Locations

• Coil #6 Connector Pinout — The 2-pin electrical connector on the ignition coil for cylinder #6 (front bank, driver's side).. One pin is the 12V+ power feed (often a Violet wire on Fords), and the other is the control signal wire from the PCM (often Violet with a Brown stripe). Testing for voltage and the PCM signal at this connector is a primary diagnostic step.
• PCM Connector C1551E, Pin 73 — At the Powertrain Control Module (PCM), which is typically located in the engine bay near the firewall or battery.. This is the specific pin on the PCM that sends the control signal to the ignition coil for cylinder #6. If there is no signal at the coil connector but the wiring is good, a technician can test for the signal directly at this pin to confirm if the PCM driver has failed.
• G100 — Located on the right front of the engine compartment.. This is a primary engine compartment ground. A loose or corroded connection at G100 can cause a wide range of seemingly unrelated electrical issues with engine controls, including erratic behavior of the ignition system.
• G101 — Located on the left front of the engine compartment.. Similar to G100, this is another critical engine bay ground point. The PCM and its related sensors and actuators rely on solid ground connections to function correctly. Poor grounding can cause incorrect readings and trigger false codes.
• Splice S127 — Located in the engine control & fuel charge harness, near the breakout to fuel injector #6.. While listed near the injector, splices in the main engine harness are potential failure points for corrosion or vibration damage. A fault in a nearby splice could potentially affect the wiring for the ignition coil circuit, causing an open or short.

Real Owner Repair Stories

• SHO Forum user 'jtreber' (2013+ Ford Taurus SHO (platform mate with same engine family)) — P0356 fault code, misfiring on cylinder 6.
  ❌ Tried (didn't work) Swapping the ignition coil from cylinder 6 to another cylinder did not make the code move. The P0356 code remained for cylinder 6.
  ✅ What actually fixed it The user did not post the final fix, but the immediate next diagnostic step recommended by another forum member was to check for a pulled pin or damaged wiring in the harness connector, and to use a noid light to verify the PCM was sending a signal, pointing towards a wiring or PCM issue rather than a coil issue.
• NHTSA ODI #11429061 — An owner reported that their vehicle, displaying codes P0351 through P0356, shut down on the interstate and would not restart, noting that the PCM was the most likely cause.

OEM Part Supersession History

• 7T4Z-12029-E → DG520 — This is a standard part number evolution for Motorcraft. DG520 is the service part number that replaces the original engineering number.
  Heads up: There are many counterfeit parts sold as 'Motorcraft DG520'. Authentic Motorcraft coils have specific molding marks and engineering numbers in the plastic that fakes often lack. Using counterfeit coils can lead to immediate failure or damage to the PCM.

Model Year Variations Within This Range

• 2008 models built on or before March 1, 2008: These models are specifically called out in TSB 13-4-17. They have a higher propensity for a failed ignition coil to damage the PCM. The official repair procedure for these vehicles, if a physically damaged coil is found, mandates the replacement of the PCM, all six coils, and all six spark plugs to prevent a repeat failure.

Diagnostic Flowchart

Other Known Issues on This Vehicle

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

• Internal Water Pump Failure 🔴 High — Common after 100,000 miles. Failure can cause coolant to mix with engine oil, leading to catastrophic engine damage if not caught early.
• Electronic Throttle Body (ETB) Failure 🔴 High — Very common. Can fail at any mileage, causing the vehicle to suddenly enter 'limp mode' with no acceleration, which is a major safety hazard. (Ref: Customer Satisfaction Program 13N03 (Expired))
• Leaking Valve Cover Gaskets 🟡 Low — Common on higher-mileage vehicles. The rear valve cover is the most common culprit.

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: A used Powertrain Control Module (PCM) from a reputable recycler can be a cost-effective option, especially if it comes from a vehicle with a known history and lower mileage. It is a viable alternative to a very expensive new OEM unit, but it must be reprogrammed for the vehicle's VIN and key information.

Donor-vehicle mileage cap: roughly under 120000 miles for the part to have meaningful remaining life.

What to inspect on the donor part:

• For a used PCM, check for any signs of water damage, corrosion on the pins, or physical damage to the case.
• Ensure the donor vehicle was not involved in a fire or major front-end collision.
• Verify the part number on the used PCM exactly matches the original unit or is a known compatible replacement.
• Ask for the VIN of the donor car to check its history if possible.

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

• Ignition Coils: Due to the high risk of PCM damage from poor quality coils on this platform, using genuine Motorcraft (DG520) coils is strongly recommended. Many forum users and mechanics report immediate or premature failure from cheap aftermarket or counterfeit coils.
• Powertrain Control Module (PCM): While a used OEM unit is an option, new aftermarket or 'rebuilt' PCMs from unknown brands should be avoided. A reputable repair service like Circuit Board Medics, which repairs the original OEM board, is a much safer alternative.

Aftermarket brands forum-validated for this vehicle:

• NGK and Denso are generally considered reliable aftermarket brands for ignition coils if Motorcraft is unavailable.

Brands owners have reported issues with on this vehicle:

• Unnamed, no-brand ignition coils from online marketplaces (e.g., Amazon, eBay) are frequently reported to fail quickly and are sometimes counterfeit. Avoid coil sets that are priced significantly lower than all other options.

Real Owner Stories

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

Related OBD-II Codes

• P0351 — Related ignition coil primary/secondary circuit code for Cylinder #1; often appears alongside P0356 in TSB 13-4-17.
• P0352 — Related ignition coil primary/secondary circuit code for Cylinder #2; identified in TSB 13-4-17 as part of the same failure pattern.
• P0353 — Related ignition coil primary/secondary circuit code for Cylinder #3; identified in TSB 13-4-17 as part of the same failure pattern.
• P0354 — Related ignition coil primary/secondary circuit code for Cylinder #4; identified in TSB 13-4-17 as part of the same failure pattern.
• P0355 — Related ignition coil primary/secondary circuit code for Cylinder #5; used during the 'coil swap' diagnostic step to confirm if a fault moves with the coil.
• P0306 — Cylinder #6 misfire code; often accompanies P0356 when the coil fails to provide spark to the cylinder.

Frequently Asked Questions