P0354 Code: Ignition Coil D Primary/Secondary Circuit
Coil D, normally the one on cylinder 4, failed its circuit check. It often shows up right after a tune-up.
At a glance
Severity: Moderate
- Meaning
- Ignition Coil D Primary/Secondary Circuit
- System
- Ignition & Misfire · Powertrain
- Safe to drive?
- With caution
- Typical repair cost
- $0–$550
- DIY difficulty
- Easy
P0354 sets when the fourth coil output misbehaves electrically: the engine computer switched coil D but did not see the current build-up or the confirmation pulse it expects. On an inline four, cylinder 4 is the last cylinder, at the transmission end of the engine. A four-cylinder with a single waste-spark pack normally has only two coil outputs, so P0354 on a four-cylinder usually means individual coils or a rail with four coils inside. The secondary side matters here too: a boot that isn't seated on the plug, water in the plug well or a plug with the wrong gap can overload the coil until its circuit fails. That is why this code so often appears soon after a spark plug job.
Can I keep driving? Short, gentle trips to a shop are usually OK while the light is steady. With a flashing light or heavy shaking, stop, because fuel from the dead cylinder is overheating the catalytic converter.
How to read P0354
- P Powertrain
- 0 Generic (SAE)
- 3 Ignition / misfire
- 54 Specific fault
Symptoms
- Miss that started right after spark plugs or coils were replaced
- Check-engine light that flashes under load, with P0304 also stored
- Worse after rain or a car wash when water reaches the plug well
- Shaking at idle that gets worse with the A/C on
- Popping or uneven exhaust note at the tailpipe
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Coil D has failed, either the winding or the built-in igniter
- Connector or coil boot not fully seated after spark plug replacement
- Water or oil in the cylinder 4 plug well, leading to a tracked boot or corroded spring
- Worn plug, wrong plug type or incorrect gap overloading the coil
- Damaged coil D connector or pigtail wiring
- Coil rail with four coils in one housing has failed on the cylinder 4 section
- Coil driver inside the engine computer has failed
Diagnosis step by step
Find cylinder 4 and check the coil layout
On inline fours it is the last cylinder at the transmission end. On a GM V8 it is second from the front on the passenger side, on a Ford V8 it is the rear passenger-side cylinder right under the cowl, and on transverse V6s it is on the radiator-side bank. If your four-cylinder has one waste-spark pack with only two coil outputs, confirm the code definition in the service information.
Tools: Flashlight
Recheck any recent plug work first
If the code showed up after new plugs, make sure the coil D connector clicked home and the boot is pushed fully down onto the plug. Confirm that the plug is the correct type and gap for your engine, because a wrong heat range or a gap that is too wide makes the coil work much harder.
Tools: Spark plug socket, Flashlight
Clear the well before pulling the plug
Pull coil D and look for water, oil or debris in the well. Blow the well out with compressed air before removing the plug, so nothing falls into the cylinder. Rust on the plug hex or a green, corroded boot spring shows water has been sitting there for some time.
Tools: Flashlight, Gloves
Inspect the boot and spring
Look for thin black carbon tracks on the boot or the coil body, cracks, and a burned or rusty contact spring. Compare it with the boot from cylinder 3. A tracked boot lets the spark jump to ground instead of the plug, and over time that also destroys the coil.
Tools: Flashlight
Spark test cylinder 4 against cylinder 3
Fit an adjustable spark tester to coil D, set to the gap its maker recommends for coil-on-plug engines, and crank the engine. Then repeat on cylinder 3. A weak, orange or missing spark on cylinder 4 with a strong blue spark on cylinder 3 confirms coil D or its supply.
Tools: Spark plug socket, OBD-II scanner
Fix the water or oil source
Clear clogged cowl drains, reseal the valve cover or plug tube seals, and make sure the coil's seal sits properly in the well. Replacing the coil without stopping the water or oil only buys a few weeks.
Tools: Screwdriver, Flashlight
Where the parts are
- 1Ignition coil
- 2Spark plug
- 3Fuel injector
- 4Camshaft sensor
- 5Crankshaft sensor
- 6Engine computer (ECM)
- 7Intake manifold
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Reseat coil D connector and boot (after plug job) | Yes | $0–$60 |
| Replace coil D and plug 4 | Yes | $100–$300 |
| Replace coil boot and spring only (where sold separately) | Yes | $20–$80 |
| Replace four-coil ignition rail | Yes | $200–$550 |
| Valve cover gasket or cowl drain repair to stop water or oil | No | $150–$500 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Notes by brand
Ford
Older Ford 4.6L and 5.4L two-valve V8s (F-150, Expedition, Crown Victoria) had shallow plug threads in the head and are well known for blowing a spark plug out of its hole. The ejected plug usually wrecks the coil on top of it and sets a coil circuit code along with the misfire. If the engine suddenly ticks loudly and a coil sits loose, suspect this before just replacing the coil.
Field data
| Ford | 2 | Edge, Escape Hybrid | |
|---|---|---|---|
| Toyota | 2 | Corolla, RAV4 |
Source: NHTSA Complaints API (US government open data), analyzed by DTC mention.
Emissions / smog test impact
Will fail
Any coil circuit code with the check-engine light on fails an OBD-II emissions test. If you fixed a connector left loose after a tune-up, the code clears itself after a few good drive cycles, but readiness monitors still need time after a manual code clear.
Frequently asked questions
The code appeared right after new spark plugs. What went wrong?
Usually a coil connector that didn't click home, or a boot that isn't fully on the plug. Less often, the wrong plug or gap was used, or a boot was torn on removal. Recheck cylinder 4 first before buying parts.
My four-cylinder has one coil pack. How can it set P0354?
Many single-piece coil units are really four individual coils in one rail, each with its own driver, so each can set its own code. A true waste-spark pack only has two coils for four cylinders, and on those engines a P0354 is uncommon.
Why is there water in the cylinder 4 plug well?
Blocked cowl or windshield drains, a torn coil seal or a pressure washer aimed at the engine. On engines where cylinder 4 sits under the cowl, rainwater has a short path straight into the well.
Can I just dry the well and keep the old coil?
If the coil sets no more codes and the spark test is strong, sometimes yes. But a boot that has carbon tracks or a rusty spring usually fails again, so replace at least the boot if it is sold separately.