Fix P0356: Mechanic’s solutions that WORKED

The code P0356: “Ignition Coil F Primary/Secondary Circuit Malfunction,” points to issues related to the ignition coil on cylinder 6, wiring or connection problems in the coil circuit, or potential ECM concerns. Diagnosing and addressing this code is essential to maintain a well-functioning engine.

P0356 quick overview

Meaning	P0356: Ignition Coil F Primary/Secondary Circuit Malfunction
Is it serious?	It can affect engine performance and fuel efficiency, so it should be addressed promptly.
Possible causes	– Faulty ignition coil on cylinder 6. – Wiring or connection issues in the ignition coil circuit. – Problems with the Engine Control Module (ECM).
How to diagnose?	Inspect and test the ignition coil on cylinder 6. Check the wiring and connections related to the ignition coil circuit. Use a scan tool to diagnose any ECM issues. Perform a systematic diagnostic approach, including road tests and customer feedback, to accurately pinpoint the problem.

How to fix P0356 – learn from mechanics

I looked into P0356 service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.

Case #1: Mercury

Vehicle Information:

• 1999 Mercury Grand Marquis GS 4.6L

Issue + Repair History:

• Intermittent misfire with codes P0351 and P0356 for primary ignition failure on cylinders 1 and 6.
• Scoped ignition system and amp ramped coils; no issues found.
• Replaced coils on cylinders 1 and 6.
• Crankshaft sensor resistance measured at 255 ohms (out of spec).

Other OBD2 Codes + Test Results:

• None mentioned.

Suggestions to Fix Issue:

• Check wiring harness for chafing and conduct a wiggle test.
• Consider replacing the PCM (Powertrain Control Module).
• Inspect and clean the EGR (Exhaust Gas Recirculation) ports.
• Examine timing chain and guide system for excessive play.
• Current ramp coils for further diagnosis.

Final Fix:

• Replacing the PCM was suggested as the potential solution to the issue. The technician suspected that the PCM was causing intermittent coil circuit open codes (P0351 and P0356), which were not related to misfires but rather a wiring problem. The issue occurred while coasting down from around 50mph and then during acceleration after slowing down, setting the codes. Replacing the PCM was considered a likely solution, although it had not been confirmed at the time of the discussion.

Case #2: Chrysler

Vehicle Information:

• 2002 Chrysler Sebring LXi 2.7L

Issue + Repair History:

• Intermittent loss of cam or crank sensor (P1391 code).
• Replaced pigtail on the cam sensor due to an intermittent connection.
• Car started bucking during a test drive and set codes P0356 and P0354 (#6 and #4 coil circuits).
• Checked wiring harness from PCM to coils (no issues found).
• Replaced PCM and reflashed it, but problem persisted.
• Misfires were observed late in a prolonged test drive.

Other OBD2 Codes + Test Results:

• None mentioned.

Suggestions to Fix Issue:

• Swap coils with other cylinders to see if the misfire moves with the coil.
• Check the ground control to the coil from the ECM (Engine Control Module).
• Scope the secondary system on the coil.
• Open the harness and check the splices for issues.
• Load test the wires in the harness.
• Examine corroded or chafed wiring on the driver’s side of the engine above the transmission.
• Move coils to different locations to see if the fault code changes with the coil location.

Final Fix:

• The issue was resolved by replacing the OEM crank sensor. The technician discovered that the crank sensor was the root cause of the problem, leading to misfires and setting codes P0356 and P0354.

Case #3: Ford

Vehicle Information:

• 2008 Ford Expedition XLT 5.4L

Issue + Repair History:

• Coils and plugs were replaced three months ago.
• The car started to misfire and run rough, especially when the A/C was turned on.
• It would start to misfire but could be temporarily fixed by turning off and restarting the engine.
• Code P0356 (Circuit F malfunction) was present, but the misfire was intermittent and didn’t occur consistently.

Other OBD2 Codes + Test Results:

• None mentioned.

Suggestions to Fix Issue:

• Check the coil wiring for any breaks near the connector.
• Ensure that the replaced ignition parts are Motorcraft, as non-OEM parts may not last.
• Check for coil driver circuit issues inside the ECU (Engine Control Unit).
• Verify if the engine is prone to plug stripping or breakage, as this could lead to misfires.
• Check the wiring harness near the AC accumulator for rubbing issues, which could cause electrical problems.
• Inspect battery terminals for corrosion or oxide buildup, as this may affect the electrical circuit.
• Check grounds, especially the one on the back of the left head.

Final Fix:

• The issue was resolved by replacing a faulty coil (cylinder 6) after finally getting it to run rough. The technician identified that the coil was bad, and replacing it fixed the problem. The customer had previously replaced coils and plugs with non-OEM parts, which may have contributed to the issue.

Case #4: Toyota

Vehicle Information:

• 2004 Toyota Camry LE 3.0L

Issue:

• Check engine light is on.
• OBD2 codes: P0353 (Ignition coil “C” primary/secondary circuit) and P0356 (Ignition coil “F” primary/secondary circuit).
• Customer bought the car from an auction with these codes.
• It appears that the coil on cylinder #3 is a new one.
• Concerns about previous work on the car before it went to the auction.

Suggestions to Fix Issue:

• Check for a wiring problem in the crank sensor circuit.
• Verify the condition of the reluctor on the crankshaft, as a broken tooth could cause issues.
• Check with the dealer for updated coils for this application.
• Don’t immediately replace coils without proper testing; follow the Possible Causes laid out in the diagnostic procedure.
• Check for damaged wiring or connectors in the IGF and IGT1-6 circuits from the ignition coil with the igniter assembly.
• Check for a defective No. 3 ignition coil with igniter assembly.
• Inspect the ECM for defects.

Final Resolution:

• The customer took the car to a Toyota dealer to have the catalytic converter replaced. There were various suggestions from different technicians, including checking the ignition system, crank sensor circuit, and timing belt alignment. Since the car was still under warranty for the catalytic converter, they decided to address that issue first and see if it resolved the check engine light problem. If the issue persisted, they would explore other possible causes.

Case #5: Ford

Vehicle Information:

• 1999 Ford Expedition Eddie Bauer 5.4L

Issue:

• Intermittent check engine light with code P0356 (Ignition coil a through j primary secondary circuit malfunction).
• Replaced the #6 cylinder plug and ignition coil.
• Checked for head gasket leaking inside the cylinder and found it to be okay.
• Checked CKP (Crankshaft Position) sensor with a reading of 290 ohms, within the specification range of 290 – 390 ohms.

Resolution:

• The issue was resolved by replacing the CKP (Crankshaft Position) sensor.
• Thanks to Dan from Washington for suggesting the CKP sensor as the fix.

Additional Suggestions:

• In cases of intermittent misfires and ignition coil issues on Ford engines, it’s important to consider the condition of spark plugs and coils.
• Pay attention to the firing order and the possibility of misfires affecting adjacent cylinders in the firing order.
• Check for vacuum leaks in the intake manifold, as they can also cause misfires.
• When diagnosing sensor issues, consider temperature sensitivity and the possibility of the sensor going out of range during warm-up.
• Verify the fix with road tests and customer feedback.

Advice	Diagnostic Step Description
Check spark plugs and ignition coils	Inspect the condition and performance of spark plugs and ignition coils.
Verify firing order	Ensure that the firing order is correct to prevent misfires in adjacent cylinders.
Check for vacuum leaks	Investigate the intake manifold for vacuum leaks, which can lead to misfires.
Consider temperature sensitivity	When diagnosing sensor issues, consider temperature sensitivity and sensor behavior during warm-up.
Systematic diagnostic approach	Use a systematic diagnostic approach, including road tests and customer feedback, to accurately pinpoint the problem.