P04F1: EVAP system low purge flow: the computer sees less fuel vapour moving from the charcoal canister to the engine than expected

EVAP system low purge flow detected

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

Honda's bulletin and the NHTSA complaints describe a check engine light with this code but give no sourced guidance on how soon to act, so we have not rated it.

Source: how we rate severity

P04F1 in short

P04F1 means the engine computer sees too little fuel vapour being drawn from the EVAP canister into the engine. On Honda and Acura models it is often stored with P0441. The purge valve is the part most often replaced in owner reports, but hoses and other causes need ruling out first.

The EVAP system traps fuel vapour in a charcoal canister, then the purge valve lets the engine draw it in. The computer checks that vapour really flows when it opens the valve. Honda's bulletin A21-081 words P04F1 as EVAP system low purge flow detected.

Owner readouts from Honda and Acura vehicles show P04F1 together with P0441, the general purge flow code. In two reports a replaced purge valve cleared the light, but in another a dealer found the hoses clear and the problem returned.

A third owner was told the cause was fuel injectors because P0172 was also stored. That is a dealer opinion in an owner report, so treat it as a possibility to test.

Most likely causes

Cause 1: Purge valve not opening or flowing enough
Supported by vehicle data
Why it ranks here
Two NHTSA complaints from Honda and Acura owners say replacing the purge valve (and in one case the joint purge valve) cleared the light or was recommended by the dealer. A third says the fault returned within a year.
What would change this
Rises if the valve does not click or flow when commanded. Falls if it passes a flow test or the code returns after replacement.
How to test the evap canister purge valve
Cause 2: Blocked or kinked purge hose or line
Possible — needs testing
Why it ranks here
The dealer in one complaint inspected the purge hoses and found no blockage, so this is a check, not a proven cause.
What would change this
Rises if a hose is kinked, pinched or does not pass air. Falls if hoses are clear and hold vacuum.
Cause 3: Fuel mixture or injector problem (P0172 also stored)
Possible — needs testing
Why it ranks here
One owner was told the cause was fuel injectors when P0172 was stored with P04F1. It is a single report and not tied to the code.
What would change this
Rises if P0172 is stored and trims are rich. Falls if no mixture code is stored.

What to test first

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

Step 1: Read all stored codes and freeze-frame data and note whether P0441 or a mixture code such as P0172 is stored with P04F1.
Low riskTool: OBD-II scan tool
- IfP0441 and P04F1 are stored together
  It meansLook at the purge flow path.
  Go to step 2
- IfP0172 or another mixture code is stored too
  It meansCheck fuel trims and injectors as well.
  Points to: Fuel mixture or injector problem (P0172 also stored)
Step 2: Ask a Honda or Acura dealer whether bulletin A21-081 or any later one applies to your VIN. Note that one Acura MDX dealer said A21-081 does not apply to that model.
Low risk
- IfA bulletin applies
  It meansFollow the dealer's procedure first.
  Points to: Purge valve not opening or flowing enough
- IfNo bulletin applies
  It meansCheck the purge hoses and valve.
  Go to step 3
Step 3: With the engine off and cool, look at the purge hoses and connectors between the canister, the purge valve and the intake for kinks, cracks or loose fittings.
Low riskTool: flashlight
- IfA hose is pinched, cracked or loose
  It meansRepair the hose and recheck.
  Points to: Blocked or kinked purge hose or line
- IfHoses look fine
  It meansHave the purge valve flow-tested.
  Go to step 4
Step 4: Have the purge valve checked for opening and flow with a scan tool that can command it.
Best left to a shopTool: bidirectional scan tool
Warning:The EVAP system holds fuel vapour. Keep sparks and open flame away and have a shop handle the work.
- IfThe valve does not open or flow when commanded
  It meansThe purge valve is the likely fault.
  Points to: Purge valve not opening or flowing enough
- IfThe valve works
  It meansRecheck hoses and other stored codes.
  Go to step 3

Symptoms

Check engine light with P0441 and P04F1 stored
Often no change in how the car drives

How to fix

Step 1: Ask a dealer whether a bulletin applies to your VIN.
Step 2: With the engine off and cool, look over the visible purge hoses for kinks or loose connections.

Parts and cost context

EVAP canister purge valve:The purge valve was the part replaced in the owner reports; test it before buying one. Labour varies; get a quote.

Labor varies by vehicle and shop; get a quote before you approve a repair.

Compare used part prices on PartPriceGuide

On your vehicle

Honda

2017–2022 · CR-V
Supported by vehicle data
Honda bulletin A21-081 covers CR-V models that set P0441 with P04F1. An owner of a 2018 CR-V had the purge valve replaced. Bulletin status is not verified.
2019 · Pilot
Supported by vehicle data
2019 Pilot owners report P04F1 with P0441. One cleared it by replacing the purge valve and joint purge valve; another was told fuel injectors. A21-081 is not listed for the Pilot.

A21-081Status unverified
MIL with P0441 and P04F1
2017–2022cr-v · NHTSA 10202869
Service information for a CR-V that sets P0441 and P04F1. The NHTSA summary does not say what the repair is.
We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

Acura

2018 · MDX
Supported by vehicle data
A 2018 MDX owner reports P0441 and P04F1 and was told by the dealer that A21-081 does not apply.

All EVAP (evaporative emissions) codes

P04F1 questions

What is the difference between P0441 and P04F1?

P0441 is the general purge flow code. In Honda's bulletin, P04F1 is the specific low-purge-flow code that shows up with it.

Sources and review

Honda A21-081: MIL with P0441 and P04F1 (CR-V) — American Honda (via NHTSA manufacturer communications flat file)
NHTSA complaint ODI 11474249 — NHTSA (consumer complaint database, local flat-file cache)
NHTSA complaint ODI 11563010 — NHTSA (consumer complaint database, local flat-file cache)
NHTSA complaint ODI 11761856 — NHTSA (consumer complaint database, local flat-file cache)
NHTSA complaint ODI 11591265 — NHTSA (consumer complaint database, local flat-file cache)

Last reviewed: October 16, 2026
Written by: Saurabh K.
Editorial review: Pending
Technician review: Technician review pending

This page explains what a code usually means; it is not a substitute for a professional inspection. How we source and review · Report an error

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

Most likely causes

Cause 1: Purge valve not opening or flowing enough

Cause 2: Blocked or kinked purge hose or line

Cause 3: Fuel mixture or injector problem (P0172 also stored)

What to test first

Step 1: Read all stored codes and freeze-frame data and note whether P0441 or a mixture code such as P0172 is stored with P04F1.

Step 2: Ask a Honda or Acura dealer whether bulletin A21-081 or any later one applies to your VIN. Note that one Acura MDX dealer said A21-081 does not apply to that model.

Step 3: With the engine off and cool, look at the purge hoses and connectors between the canister, the purge valve and the intake for kinks, cracks or loose fittings.

Step 4: Have the purge valve checked for opening and flow with a scan tool that can command it.