P1399 On Honda and Acura, a random misfire that the computer cannot pin on one cylinder

Honda random misfire (P1399)

Severity not verified — if the car runs badly, have it inspected

We have not sourced a severity ruling for P1399. A misfire can still damage the catalytic converter, so have a shop look at it soon, and treat a flashing check engine light as urgent.

Source: how we rate severity

P1399 in short

On Honda and Acura, P1399 points to a random misfire: the engine is misfiring, but not on one cylinder. A mechanic cites a valve adjustment that is due or a blocked EGR passage. Other makers use this code differently, so we have not verified their meanings.

P1399 is a Honda-specific code. It is not on the generic list, so scan tools and shops outside Honda sometimes cannot say what it means. Owners in NHTSA complaints describe shops sending them to Honda to find out.

Honda's own service bulletin 060103 groups P1399 with misfire codes P0301 to P0306 on Odyssey, Pilot, TL, CL and MDX models that run rough from 40 to 70 mph. A CR-V owner reports P1399 alongside P0300 to P0304.

A mechanic answering a question on a 2003 Pilot names a valve adjustment that is due and a blocked EGR passage as the usual causes. Treat that as one reference, not a rule for every Honda.

Pick your make

P1399 is a manufacturer-specific code: its meaning depends on who built the car.

Other makes: meaning not verified. Check with a scan tool that reads manufacturer definitions.

Most likely causes

These are general causes for this code across vehicles. None is specific to one make or model.

  1. Valve clearances out of adjustment

    Possible — needs testing
    Why it ranks here
    A mechanic answering a 2003 Honda Pilot question says a valve adjustment usually fixes this code; it is one source, so it is a lead rather than a rule.
    What would change this
    Rises if the engine has high mileage and the valve adjustment is overdue or the engine ticks. Falls if the clearances measure in specification.

  2. Blocked exhaust gas recirculation (EGR) passage

    Possible — needs testing
    Why it ranks here
    The same mechanic names a blocked EGR passage as another source of this code.
    What would change this
    Rises if the misfire is worst at steady cruise and the EGR passage is clogged with carbon. Falls if the EGR flow checks out.

  3. Ignition or fuel faults that cause misfires generally

    Possible — needs testing
    Why it ranks here
    Honda bulletin 060103 places P1399 with the individual cylinder misfire codes on engines that run rough at 40 to 70 mph, so the usual misfire causes still need ruling out. The NHTSA summary gives no repair.
    What would change this
    Rises if individual cylinder misfire codes are stored too, or spark plugs and coils are old. Falls if ignition and fuel parts test good.

What to test first

Start at step 1. Each result tells you what it means and where to go next.

  1. Read all codes and freeze-frame data. Note which cylinder misfire codes (P0301 to P0306) are stored with P1399, and whether the light flashes.

    Low riskTool: OBD-II scan tool

    • IfThe light is flashing

      It meansMisfire is severe; stop driving and have it inspected.

      Go to step 2

    • IfSingle-cylinder codes are stored too

      It meansDiagnose those cylinders as well.

      Go to step 2

    • IfOnly P1399 is stored

      It meansCheck maintenance history, including the last valve adjustment.

      Go to step 2

  2. Have a shop check valve clearances, the EGR passages and the ignition parts, with Honda service information for your model.

    Best left to a shopTool: valve clearance gauges, scan tool, vehicle service information

    Warning:Valve adjustment and EGR service involve hot engine parts. Leave it to a shop.

Symptoms

  • Rough running, often between 40 and 70 mph
  • Check engine light on
  • Flashing check engine light Gets more serious: stop and have it checked.
  • Loss of power or poor fuel economy

How to fix

On your vehicle

Honda

  • 2003 · Pilot

    Supported by vehicle data

    Honda bulletin 060103 covers a rough-running 2003 Pilot with P1399. A mechanic also cites valve adjustment or a blocked EGR passage on a 2003 Pilot.

  • 2002–2003 · Odyssey

    Supported by vehicle data

    Honda bulletin 060103 covers a 2002-2003 Odyssey that runs rough at 40 to 70 mph with P1399. Whether the bulletin is still current is not verified.

  • 060103Status unverified

    Engine runs rough at 40 to 70 mph with P0301 to P0306 and P1399

    2002–2003odyssey, pilot · NHTSA 10002700

    Service tips for a rough-running engine with misfire codes and P1399 stored. The NHTSA summary does not give the repair.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

Acura

  • 2000–2003 · TL

    Supported by vehicle data

    Honda bulletin 060103 covers a rough-running TL with P1399 and P0133. Whether the bulletin is still current is not verified.

  • 2001–2002 · MDX

    Supported by vehicle data

    Honda bulletin 060103 covers a rough-running MDX with P1399. Whether the bulletin is still current is not verified.

  • 060103 (Acura)Status unverified

    Engine runs rough at 40 to 70 mph with P0301 to P0306, P1399 and P0133

    2000–2003tl, mdx · NHTSA 10002693

    Service tips for a rough-running engine with misfire codes, P1399 and P0133 stored on TL, CL and MDX. The NHTSA summary does not give the repair.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • P0300Random or multiple-cylinder misfire detected

    Same system Supported by vehicle data

    P0300 is the generic random misfire code. A CR-V owner reports P0300 to P0304 together with P1399.

All Misfire codes

P1399 questions

What does P1399 mean on a Honda?

It points to a random misfire detected by the engine computer. It is Honda-specific, so it is not on the generic code list.

Does P1399 mean the same on other brands?

Not necessarily. We have only sourced the Honda and Acura meaning. Other makers use this number for different faults.

Sources and review

  1. Q: OBD code P1399 (Honda Pilot) — YourMechanic
  2. Honda service bulletin 060103 (NHTSA 10002700 and 10002693): engine runs rough 40 to 70 mph with P0301-P0306 and P1399 — American Honda Motor Co.
  3. NHTSA complaint ODI 10443164: Honda CR-V 2000, P0300-P0304 and P1399 stored — NHTSA Office of Defects Investigation
Last reviewed
Written by
Saurabh K.
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