P1399Manufacturer-specific code

P1399 Code: Random Misfire Detected (Honda)

On Honda and Acura, the P1399 code means random misfires were detected. The engine shakes at idle. On many VTEC Hondas the typical cause is valve lash that is out of adjustment.

Severity
High
Can I keep driving?
Yes, but with caution
Estimated cost
$20 to $400
Difficulty
Medium
System
Ignition and Misfires
Applies to
Depends on the manufacturer

Common in: Honda

Updated Reviewed by Renzo Chacca

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What the P1399 code means

P1399 is a manufacturer-specific code: the 1 in the second position means each automaker defines what it stands for, not the generic standard. The most widespread definition is the one used by Honda and Acura. If your vehicle is another brand, confirm the code text with a scan tool that supports that manufacturer.

ManufacturerMeaning of P1399
Honda and AcuraRandom misfire detected

Honda uses the P1399 code to flag misfires that are detected but cannot be assigned to one particular cylinder, or on older engines before the P0300 code was adopted.

It is the practical equivalent of P0300. On many Hondas with VTEC the typical cause is valve lash: valves that have tightened too far cause misfires at idle.

Before you repair anything, confirm the make, model, year and engine. With manufacturer codes, the same number can change even between engines from the same brand.

P1399 code symptoms

  • Check engine light on or flashing.
  • Engine shaking at idle.
  • Jerking when you accelerate.

Likely causes of the P1399 code

  1. Valve lash out of adjustment. Very common on Honda.
  2. Worn spark plugs or coils. Confirm it with the tests in the diagnosis section.
  3. Vacuum leaks. Confirm it with the tests in the diagnosis section.
  4. Dirty injectors. Confirm it with the tests in the diagnosis section.

How to diagnose the P1399 code step by step

  1. Read the misfire counters by cylinder.
  2. Check the spark plugs and the coils.
  3. Adjust the valve lash according to the manual.
  4. Look for vacuum leaks.

How to fix the P1399 code

  • Adjust the valve lash.
  • Replace worn spark plugs or coils.
  • Repair vacuum leaks, then clear the P1399 code and confirm the idle is smooth.

Technical reference data

  • Valve lash is set with the engine cold on most Hondas.
  • P1xxx codes are manufacturer-specific: confirm the definition with a scan tool that supports your brand.
  • Values are approximate: check the manufacturer data for your vehicle.

Brand-specific notes

Very common on the Civic, Accord, CR-V, Fit and Odyssey.

If your vehicle is another brand, check the table above for the meaning its manufacturer gives the code, and confirm it with a scan tool that supports that brand.

Frequently asked questions about P1399

What does the P1399 code mean on a Honda?
It means random misfires were detected. The engine shakes at idle, and the cause is often valve lash that is out of adjustment.
Does P1399 mean the same thing on every brand?
No. It is a manufacturer code, and on other brands it may not exist or it may mean something else.
Can I drive with a P1399 code?
Only with caution. If the check engine light is flashing, stop driving, because raw fuel from the misfires can damage the catalytic converter.
How much does it cost to fix P1399?
On a Honda the cost runs from about $20 to $400. Spark plugs or a valve lash adjustment are on the lower end, while coils or injector work costs more.
Will a P1399 code clear itself?
Not for long. The cause, such as tight valves or worn plugs, stays in place, so the misfires and the code return.
What is the most common cause of P1399?
Valve lash that is out of adjustment on VTEC Hondas. Worn spark plugs and coils and vacuum leaks are the next things to check.

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Questions about the P1399 code

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