P0352
- Powertrain
- Generic (SAE)
- Emissions
Get it looked at now
A coil circuit fault normally means a dead cylinder. Unburned fuel and oxygen pass into the catalytic converter and can overheat it within minutes of sustained running. A flashing MIL confirms damage is accumulating right now.
- Safe to drive
- Flashing light: stop driving and tow. Steady light with a rough engine: shortest possible trip to a shop.
Ignition Coil "B" Primary/Secondary Circuit Malfunction (Cylinder 2)
The engine computer sent a fire command to ignition coil B and did not get the electrical response it expected back. That cylinder is likely not firing, and the computer usually shuts the coil off to protect its own driver circuit.
The PCM switches the coil primary winding to ground through an internal driver and monitors that circuit. An open primary, a short to ground, a short to battery voltage, or a missing ignitor confirmation signal will all set this code. Coil B does not universally mean cylinder 2 - most manufacturers map A/B/C/D to cylinders 1/2/3/4, but on wasted-spark and coil-pack systems a single coil serves two cylinders, so confirm the mapping in service data for your specific engine before condemning anything.
How the car detected itThe driver circuit monitors current flow during dwell and the inductive voltage spike when the coil field collapses. No current means an open circuit. Excess current means a short. Some designs, such as Toyota IGF-line systems, require the coil's integrated ignitor to return a confirmation pulse, and a missing pulse sets the code and can trigger fuel cut to that cylinder. The code reports the circuit, not the health of the coil itself.
A trouble code records what a control module measured. It does not identify which part failed. Test before replacing anything.
- Safe to drive
- Flashing light: stop driving and tow. Steady light with a rough engine: shortest possible trip to a shop.
- Urgency
- Get it looked at now
- Will it pass emissions
- No
- If ignored
- Raw fuel entering the catalyst can melt the substrate, turning a coil repair into a converter replacement several times the cost. Fuel also washes oil off that cylinder's bore, accelerating ring and wall wear, and dilutes the engine oil on sustained misfire.
- Check engine light
- Solid
- Clearing the light
- A completed drive cycle is normally required before the monitor re-runs and the light can clear.
These are the causes this code can have. For the order to work through them in, see what to check first.
| # | Cause | How often | Component |
|---|---|---|---|
| 1 | Coil primary winding open or shorted | Very common | — |
| 2 | Wiring or connector fault | Common | — |
Ordering reflects how often each cause is responsible in general, not a probability for your vehicle. Confirm by testing.
In order. Each of these is cheaper or faster than what follows it, and each one can make the rest unnecessary.
Whether the check engine light is flashing
A flashing MIL means catalyst-damaging misfire is happening now and changes the answer from drive it carefully to tow it.
Any companion misfire codes such as P0302 stored alongside
Confirms which physical cylinder the coil letter maps to on your engine and confirms the cylinder is actually dead.
The coil connector - unlatched, corroded, or pins pushed back
Costs nothing, takes a minute, and a disturbed connector after recent service is a common cause.
Oil pooled in the spark plug tube or a swollen coil boot
Oil from leaking plug tube seals cooks coil boots and shorts secondary output. Replacing the coil without fixing the leak just kills the new coil.
Whether the engine bay was recently worked on
A harness snagged or a connector left loose during plug or valve cover work is far more likely than a random coil failure.
Read all codes and capture freeze frame
Tools OBD-II scan tool
Record every stored and pending code before clearing anything. Note RPM, load, and coolant temperature at the moment of the fault. A fault that only appears cold, or only under load, points at a marginal connection rather than a dead coil.
ExpectedP0352 with a matching cylinder misfire code. Freeze frame conditions you can try to reproduce.
Identify which cylinder coil B actually is
Tools Service information
Look up the coil lettering for your engine in service data. Do not assume B equals cylinder 2. On wasted-spark systems the coil fires a pair of cylinders and the misfire will appear on both.
ExpectedA definite cylinder number for coil B from service data, not an assumption.
Swap the suspect coil with a known-good neighbor
Tools Socket set, scan tool
With the engine cold and the battery disconnected, move the suspect coil to an adjacent cylinder and move that cylinder's coil into the suspect position. Clear codes, run the engine, and see where the fault reports. This is the most decisive test available without instrumentation on a coil-on-plug system.
ExpectedIf the code and misfire follow the coil to the new cylinder, the coil is at fault. If the fault stays at the original cylinder, the coil is good - look at the wiring, the connector, the secondary path at that cylinder (boot, plug, plug wire, oil in the plug tube), and only then the PCM driver.
Check power and ground at the coil connector
Tools Digital multimeter, backprobe leads
Key on, engine off, backprobe the coil supply pin against a known-good ground. Then check the coil ground path if the design uses a dedicated one. Wiggle the harness while watching for the reading to drop out.
ExpectedSupply should read within about half a volt of battery voltage. Anything meaningfully lower indicates resistance in the feed.
Verify the trigger signal from the PCM
Tools Oscilloscope, or LED test light as a rough substitute
Backprobe the coil control wire while cranking or running. A scope showing the dwell and firing spike is far more informative than a meter. If supply and ground are good but there is no trigger, the fault is upstream in the harness or the PCM driver.
ExpectedA clean square dwell period ending in a sharp inductive spike, repeating with engine speed.
Inspect the spark plug and secondary path
Tools Spark plug socket, gap gauge, multimeter
Pull the plug for that cylinder. Look at gap, erosion, fouling, and cracked insulator. A worn plug raises the voltage the coil must produce and is a frequent reason coils fail early. On systems with plug wires, check the wire resistance and inspect for arc tracks.
ExpectedGap within the plug's specification, which is vehicle-specific. No oil, no carbon bridging, no cracks.
Measure coil winding resistance if the design allows it
Tools Digital multimeter
Only useful on coils without an integrated ignitor. Many modern coil-on-plug units contain driver electronics and cannot be judged by resistance at all. Winding resistance specifications vary by manufacturer, so compare against the figure in service data or against a known-good coil off the same engine.
ExpectedA stable reading closely matching a known-good coil off the same engine. An open or near-zero reading condemns it; anything else needs the service data figure, and a coil with an integrated ignitor cannot be judged this way at all.
Perform a harness wiggle test with the code active
Tools Scan tool with live data
With the engine idling and the fault present, gently flex the harness from the coil back toward the loom, paying attention to points where it passes near hot exhaust or a sharp bracket edge. Watch live misfire counters as you go.
ExpectedMisfire counts spiking as you disturb a specific section of harness localizes a chafe or broken conductor.
| Repair | Only after you confirm | Typical cost | Who |
|---|---|---|---|
| Replace the affected ignition coil | The code and the misfire follow the coil when swapped to another cylinder, or the primary winding measures open on a coil without an integrated ignitor. | $90–$320 | DIY |
| Repair or replace the coil harness section or connector | Supply, ground, or trigger signal is missing or intermittent at the coil while the coil itself tests good in another position. | $120–$450 | DIY |
| Replace spark plugs | Plug inspection shows excessive gap, heavy erosion, fouling, or a cracked insulator. | $120–$500 | DIY |
| Replace valve cover gasket and spark plug tube seals | Oil found standing in the plug tube and saturating the coil boot. | $200–$650 | DIY |
| Repair or replace the PCM ignition driver | Good coil, good supply and ground, and no trigger output from the PCM with the harness verified continuous and unshorted. | $700–$2,000 | Shop |
Coil-on-plug replacement is cheap and quick on most transverse four-cylinder engines. It gets expensive on V6 and V8 layouts where the rear bank sits under an intake manifold that has to come off, and on engines where plug tubes are buried. Figures are US independent-shop ranges, parts plus labor.
- Assuming coil B is cylinder 2 on every engine and replacing the wrong coil.
- Replacing the coil without inspecting the spark plug - a worn plug destroys the replacement coil the same way it destroyed the first one.
- Fitting a new coil into a plug tube full of oil, without addressing the leaking valve cover or tube seals.
- Replacing all coils as a set on the first fault, when a swap test would have identified the failed coil first.
- Clearing the code and continuing to drive with a flashing MIL, which converts a modest repair into a converter replacement.
- Condemning the PCM before checking the connector and the harness section that runs near the exhaust.
- Ignition Coil
- Ignition Coil Wiring
- Definition
- Generic code set (SAE J2012 / ISO 15031-6) via the OBDexopen database, dedicated to the public domain under CC0-1.0.
- Diagnostic guidance
- Written and reviewed in-house. See our editorial policy.
- Review status
- Reviewed
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