Can a bad ground cause P0301?

Yes, on Altimas a corroded engine-to-chassis ground strap can create coil-circuit voltage drops that mimic a failing coil. Worth a 5-minute inspection.

How do I know which one is cylinder 1?

On the QR25DE, cylinder 1 is the cylinder closest to the timing chain (passenger side on FWD Altima). Always confirm in your factory service manual — manufacturers differ.

Should I replace all 4 coils together?

If the car has over 100k miles and one has failed, the others are typically 6–12 months behind. Replacing all 4 saves a future tow.

Will the misfire damage the engine itself?

Extended driving can wash oil off the cylinder wall and accelerate ring wear, plus thermal stress on the cat. Days are fine, weeks aren't.

P0301

Cylinder 1 Misfire Detected

SEVERE

SystemIgnition

Difficulty

Cost$25–$450

Read9 min

What It Means Symptoms Common Causes Diagnosis Steps How to Fix It Emissions Test?Repair Cost FAQs

By Mike Reeves

ASE Master Technician (L1 Advanced Engine Performance) · 18 yrs

Technically reviewed by Sara Lopez

Last updated June 11, 2026

What Does P0301 Mean?

P0301 is a cylinder-specific misfire code: the ECM has detected that cylinder #1 is not burning its air/fuel charge correctly. Unlike P0300 (random/multiple), this code names the offender. On a Nissan Altima with the QR25DE 2.5L four-cylinder, cylinder 1 is the front-most cylinder closest to the timing chain side.

A misfire dumps raw fuel into the catalytic converter. Each minute of driving with an active misfire degrades the cat. Treat P0301 as a same-day fix — especially if the check engine light is flashing.

Symptoms

Rough idle with distinct 'dead' cycle

You can often feel exactly when cylinder 1 drops out.

Flashing check engine light under load

Active misfire — pull over if safe.

Vibration through steering wheel at stoplights

Most pronounced in Drive with foot on brake.

Slight power loss above 3000 RPM

Engine feels 'flat' on hard acceleration.

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Common Causes

1.Failed ignition coil on cyl 1
45%
Most common on Altimas past 90k miles. Coils tend to fail one at a time.
2.Worn or fouled spark plug
25%
Carbon-fouled or worn-electrode plug stops firing reliably.
3.Leaking / clogged fuel injector
15%
Injector flow imbalance starves or floods one cylinder.
4.Low compression on cyl 1
10%
Burnt valve, worn rings, or blown head gasket between 1 and adjacent cyl.
5.Wiring / connector at coil
5%
Corroded coil connector or chafed harness, especially after engine work.

Step-by-Step Diagnosis

Confirm the misfire is still on cyl 1

Read live misfire counters. If cyl 1 has 90% of the misfires, you're aimed correctly. If counts have shifted, re-scan after a 10-mile drive.

MISFIRE COUNTS (last 1000 rev):
  CYL 1:  68
  CYL 2:   2
  CYL 3:   1
  CYL 4:   3
  → Cyl 1 confirmed

Pro TipMark the misfiring cylinder with a paint marker on the coil pack before you start swapping anything.

Swap-test coil 1 with coil 2

Move coil 1 to cyl 2 and coil 2 to cyl 1. Clear codes, drive 5 miles, and re-read. If the misfire moves to cyl 2, the coil is bad. If it stays on cyl 1, suspect the plug or injector.

Inspect the spark plug

Pull plug 1. A black, sooty plug = fuel-rich (injector stuck open). White or blistered = lean. Wet with gas = no spark. Oil-fouled = ring or valve seal issue.

WarningQR25DE plugs are deep in the head. Use a magnetic plug socket so you don't drop the plug into the well.

Swap injector or test with noid light

If coil and plug check out, swap injector 1 with injector 2. If the misfire follows, replace the injector. A noid light on the injector connector confirms the ECM is sending pulses.

Compression test

If electrical and fuel are good, do a dry then wet compression test on cyl 1. Spec is 178–220 psi. >15% variance from neighbors means internal damage.

How to Fix It

DifficultyTime 2–3 hrs

Parts needed:

Hitachi OEM Ignition Coil (Nissan QR25DE) — approx $55
NGK LZFR5AI-11 Iridium Plugs (set of 4) — approx $32
Bosch Fuel Injector (Nissan QR25DE) — approx $95

Procedure:

Let engine cool fully — at least 1 hour.
Remove engine cover (two 10mm bolts).
Unplug coil 1 connector and remove 10mm coil bolt.
Pull coil straight up without twisting.
Remove spark plug with 14mm thin-wall socket + magnetic extension.
Inspect and replace plug if worn or fouled.
Install new coil if swap-test confirmed failure.
Torque plug to 14 lb-ft, coil bolt to 7 lb-ft.
Clear codes, drive 20 miles, recheck counters.

Will It Pass Emissions?

// DECISION TREE

STARTCheck engine light on?

YES →FAIL

NO →Readiness monitors set?

YES →PASS

NO →RETESTdrive 50–100 miles to set monitors

Repair Cost Breakdown

Part / Region	DIY Cost	Shop Labor	Total Range
Northeast US	$95	$280	$280–$420
Midwest	$95	$220	$240–$380
West Coast	$110	$320	$320–$480
South	$90	$210	$220–$360

Estimates based on aggregated independent shop quotes; dealer labor adds 30–50%. Excludes diagnostic fee ($80–$150).

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FAQs

Not necessarily — P0301 just means the ECM has identified the specific cylinder. The cat damage and urgency are the same. The advantage is you know exactly where to look.

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Sources & References

§SAE J2012 — Diagnostic Trouble Code Definitions — Standardized OBD-II code definitions used by all manufacturers.
§EPA OBD Regulations (40 CFR §86.1806-05) — Federal on-board diagnostic requirements for light-duty vehicles.

Cost figures are aggregated from real customer invoices at our shop plus quotes from RepairPal and Mitchell1 labor guides. Diagnostic procedures verified against factory service information (ALLDATA / Mitchell1).

// About the author

Mike Reeves — Independent shop owner in Phoenix, AZ. Specializes in driveability diagnostics on domestic and Asian gas engines. Writes our powertrain coverage. More about our team →

Related Codes

P0420MODERATE