Applicable Systems
OBD-II
Symptoms
Cylinder 1 misfiring; rough idle, power loss; possible catalytic converter damage if persistent.
Possible Causes
- Fouled or worn spark plug
- Cracked ignition coil
- Clogged fuel injector
- Burned valve or low compression
Troubleshooting Steps
- Step 1: Swap cylinder 1 spark plug with cylinder 2
If misfire moves to cyl 2, spark plug is bad - Step 2: Swap cylinder 1 coil with cylinder 2 coil
If misfire moves, coil is bad - Step 3: Check cylinder 1 compression
Compression within spec - Step 4: Check cylinder 1 injector pulse with noid light
Injector pulses correctly - Step 5: Replace faulty spark plug or coil
Cylinder 1 fires normally
How to Reset
Clear with OBD-II scanner after repair; clear fuel trims.
Common Replacement Parts
- Spark Plug (OEM spec)
- Ignition Coil (OEM spec)
Frequently Asked Questions
- Q: How to identify which component is bad?
Swap test: move spark plug, then coil, then injector one at a time to adjacent cylinder. If misfire follows the part, that part is bad.
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Source: SAE J2012 standard DTC list + OBD-II portal
Category: OBD-II
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