Honda Insight P0301, P0302, P0303, P0304 (2010 ZE2): Cylinder Misfire — Diagnostic Guide

Honda-specific code — factory diagnostic data

P0301, P0302, P0303, and P0304 each identify a misfire in a specific cylinder (1, 2, 3, 4). On the 2010 Insight, the PCM detects misfire by monitoring crankshaft speed deceleration on each combustion event; when the PCM sees misfire counts on a specific cylinder that exceed the emissions or catalyst-damage threshold, it stores the corresponding DTC. The factory diagnostic path is a swap-based isolation sequence: exchange parts from the misfiring cylinder with parts from a known-good cylinder and watch where the misfire count follows. Whatever part follows the misfire is the failing part.

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P0301-P0304 Honda Insight Quick Answer

On the 2010 Insight, cylinder misfire is isolated by swap test: exchange the ignition coils from the misfiring cylinder with another cylinder and re-test — if the misfire moves with the coil, replace the coil. If it stays, swap spark plugs next. If still stays, swap the injector. Only when all three swaps fail to move the misfire do you move on to wiring, compression, leakdown, and VTEC rocker arm tests. Remember the Insight has two coils per cylinder (intake + exhaust side) — both fire each combustion event, so failure of either can cause misfire on that cylinder.

The Diagnostic Procedure

Tools: Honda HDS (or aftermarket with Honda engine coverage), DMM, compression tester, cylinder leak-down tester, 15 A fuse check, wiring diagram. The procedure is driven by the HDS DATA LIST showing CYL1–CYL4 MISFIRE counters and the OBD STATUS monitor result (PASSED / FAILED / EXECUTING / OUT OF CONDITION). Do not replace parts on a guess — Honda’s path is explicitly a swap test.

1. Confirm the misfire is current. Clear the DTC. Start the engine, idle in P or N. Monitor OBD STATUS for the affected DTC (P0301/P0302/P0303/P0304).
   → FAILED at idle: proceed to swap test (step 2).
   → PASSED: check CYL misfire counters in the DATA LIST for 10 minutes. If counters show misfires, proceed to step 2. If not, test-drive in the freeze-frame range (engine speed / VSS / REL TP / calc load / APP / ECT) and re-check. If nothing reproduces, fault is intermittent — check fuel-system connector tension on the misfiring cylinder’s injector.
2. Ignition coil swap test. Turn ignition OFF. Exchange the ignition coil from the misfiring cylinder with the coil from another cylinder (any cylinder without a misfire). On the dual-plug Insight, exchange either the intake-side OR exhaust-side coil — which side you swap determines which half of the ignition system you’re testing. Test-drive and re-check misfire counters.
   → Misfire moves to the other cylinder: the coil is bad — replace the coil you just moved. Jump to step 10.
   → Misfire stays on the original cylinder: coil is OK, go to step 3.
   → No misfire anywhere after swap: intermittent poor coil connector contact — re-seat and secure both connectors.
3. Spark plug swap test. Turn ignition OFF. Exchange the spark plug from the misfiring cylinder with a plug from another cylinder. Test-drive and re-check.
   → Misfire moves: replace the bad spark plug. Jump to step 10.
   → Misfire stays: plug is OK, go to step 4.
   → No misfire: intermittent plug fouling — clean and re-gap, monitor.
4. Injector swap test. Turn ignition OFF. Exchange the injector from the misfiring cylinder with an injector from another cylinder. Start the engine and idle 2 minutes, then test-drive.
   → Misfire moves: replace the bad injector. Jump to step 10.
   → Misfire stays: injector is OK, go to step 5.
   → No misfire: intermittent poor injector-connector contact — re-seat.
5. Coil power-feed check. Turn ignition OFF, disconnect the ignition coil 3P connector from the misfiring cylinder. Turn ignition ON (II). Measure voltage between coil 3P pin 3 and body ground.
   → Battery voltage: power feed OK, go to step 6.
   → No voltage: open in the wire between the coil and the 15 A fuse (exhaust side). Repair and verify.
6. Coil ground check. Turn ignition OFF. Check continuity between coil 3P pin 2 and body ground (G101).
   → Continuity: ground OK, go to step 7.
   → No continuity: open between coil ground and G101. Repair and verify.
7. Coil control circuit check. Jump the SCS line with HDS. Disconnect PCM connector C (44P). Check continuity between body ground and the PCM terminal for the misfiring cylinder (see coil PCM pin reference in the data sheet above). Then check continuity between coil 3P pin 1 and that PCM terminal.
   → Short to ground on the PCM pin: repair the short in the coil-control wire between PCM and coil. → Open in the control wire: repair the open.
   → Both checks pass: wiring is clean, go to step 8.
8. Mechanical tests. Do an engine compression test and a cylinder leak-down test. If either fails, the engine needs mechanical repair before any DTC work can verify. Then perform the VTEC rocker arm test — a stuck rocker assembly can cause cylinder-specific misfire even on a mechanically sound engine.
9. Injector power-feed and control checks. Turn ignition ON. Measure voltage between body ground and the appropriate PCM injector terminal (Cyl 1 C5, Cyl 2 C6, Cyl 3 C7, Cyl 4 C8).
   → Battery voltage present: control circuit is OK, go to resistance check.
   → No battery voltage: disconnect the injector 2P connector, measure at injector pin 1. Battery voltage there confirms power feed; no voltage means open between injector and PGM-FI main relay 1. Then check continuity between PCM pin and body ground (short) and between injector pin 2 and PCM pin (open). Repair as indicated. Finally, measure injector resistance between its pins 1 and 2: spec is 10 to 13 Ω. Out of spec = replace the injector.
10. Clear, reset, and verify. Reconnect everything. Clear the DTC with HDS. Reset the PCM. Clear the CKP pattern. Perform the PCM idle learn procedure and the CKP pattern learn procedure. Test-drive in the freeze-frame range. Re-check for pending/confirmed DTCs and monitor OBD STATUS.
    → PASSED: repair confirmed.
    → FAILED: recheck connector tension at the coil, injector, and PCM. Consider a PCM software update; substitute a known-good PCM only as last resort.

Professional tip. The dual-plug LDA engine fires both the intake-side and exhaust-side coil every combustion event. That means on the Insight specifically, the swap test needs to consider which side’s coil is being exchanged — swapping only the intake-side coils will not catch an exhaust-side coil failure. If the first coil swap doesn’t move the misfire, swap the other side before moving to step 3.

Common Causes on the 2010 Insight ZE2

Ranked by real-world frequency on the LDA engine, mapped to the step that isolates each:

• Fouled or worn spark plug. Isolated by step 3. Insight plugs live under the intake-side or exhaust-side coil and see significant cumulative heat cycles — routine replacement interval is a common prevention.
• Failed ignition coil (primary winding short or open). Isolated by step 2. Either the intake-side or exhaust-side coil on the misfiring cylinder; swap both to confirm.
• Injector electrical failure — internal short producing under-spec resistance, or open winding producing OL. Isolated by step 4 or the resistance check at the end of step 9.
• Poor connector contact at coil, plug boot, or injector — backed-out pins, corroded terminals, or failed connector latches. Cleared when a swap produces “no misfire” instead of moving the fault.
• Open in the coil control wire from PCM pin C15–C18 (intake side) or C19/C23–C25 (exhaust side) to the misfiring cylinder’s coil. Isolated by step 7.
• Mechanical fault — low compression on the affected cylinder, cylinder leak-down, or a stuck VTEC rocker assembly. Isolated by step 8. Less common than ignition/fuel causes on an engine in good general condition.
• PCM calibration / driver failure. Last candidate after every other check is clean. Honda may have released a PCM software update that applies — install before substituting a known-good PCM.

Severity & Driving

Cylinder misfire is a high-priority powertrain fault. Frequent misfires overwhelm the catalytic converter with raw fuel and damage it — if the MIL is flashing, the PCM has detected catalyst-damaging misfire severity; pull over and arrange transport to a workshop. Steady (non-flashing) MIL with a cylinder-specific code means continue only to the workshop at low load. On the IMA hybrid, cylinder misfire also disrupts the hybrid strategy — the system assumes balanced combustion when deciding assist / regeneration duty, and imbalanced cylinders can produce rough hybrid transitions. Do not defer the repair.

Last updated: April 19, 2026