P1491: On Honda, the EGR valve does not lift enough; on Nissan, a fault in the EVAP vacuum cut valve bypass valve
EGR valve insufficient lift (Honda) / vacuum cut valve bypass valve (Nissan)
Severity: Severity not verified — if the car runs badly, have it inspected
The sources read describe the Honda and Nissan meanings but give no driving-risk rating. Honda lists engine hesitation or surging as a possible effect.
P1491 in short
P1491 means different things by make. On Honda it means the EGR valve is not lifting enough, often from a dirty valve or clogged port. On Nissan it is a fault in the EVAP vacuum cut valve bypass valve. Other makes may differ. Honda lists hesitation or surging; severity is not verified.
On Honda, the computer checks the EGR valve lift and stores P1491 if the lift is too small. Honda's warranty extension says contamination of the valve or clogging of the EGR port may cause P1491, P0401 or hesitation and surging.
On the Nissan Frontier and Xterra, the code is about the EVAP vacuum cut valve bypass valve. Nissan's 2001 bulletin links it to difficulty refuelling, which points to the EVAP system rather than EGR.
This page speaks for Honda and Nissan only. Other makes that use P1491 may mean something else.
Pick your make
P1491 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
Cause 1: EGR valve contamination or clogged EGR port (Honda)
Supported by vehicle data- Why it ranks here
- Honda's warranty extension covers EGR valve contamination or port clogging that may cause P1491, P0401 or hesitation on 1999-2003 Odyssey and 2003 Pilot.
- What would change this
- Rises if the valve or port shows carbon and the valve does not lift. Falls if the valve lifts freely.
Cause 2: EGR valve or its wiring (Honda)
Common general cause- Why it ranks here
- Honda's service manual page lists a faulty valve and opens or shorts in the wiring between the valve and the computer.
- What would change this
- Rises if the circuit tests faulty or the valve has abnormal resistance. Falls if the wiring tests fine.
Cause 3: Engine computer fault (Honda)
Possible — needs testing- Why it ranks here
- The same manual page lists the engine computer after the valve and wiring.
- What would change this
- Rises only after the valve and wiring pass.
Cause 4: EVAP vacuum cut valve bypass valve fault (Nissan Frontier, Xterra)
Supported by vehicle data- Why it ranks here
- Nissan ITB02015 gives P1491 as the vacuum cut valve bypass valve, and NTB01039 covers a MIL with P1491 and difficulty refuelling on 2001 Frontier and Xterra. The summaries do not give the repair.
- What would change this
- Rises on a 2001-2003 Frontier or Xterra with a refuelling problem. Falls on other makes or if the EVAP system passes testing.
What to test first
Start at step 1. Each result tells you what it means and where to go next.
Step 1: Note the make: on a Honda, inspect the EGR valve and port; on a Nissan Frontier or Xterra, ask a dealer about the EVAP bulletin.
IfHonda: P0401 is also stored or the engine hesitates or surges
It meansInspect the EGR valve and port for contamination.
Points to: EGR valve contamination or clogged EGR port (Honda)
IfHonda: no other EGR code
It meansTest the valve circuit.
IfNissan Frontier or Xterra
It meansFollow the EVAP bulletin steps with a dealer.
Points to: EVAP vacuum cut valve bypass valve fault (Nissan Frontier, Xterra)
Step 2: With a scan tool and multimeter, check the EGR valve and the wiring between the valve and the computer for opens and shorts.
Warning:The EGR valve and its piping can be very hot after driving; let the engine cool first.
IfA circuit fault is found
It meansRepair the wiring or replace the valve.
IfThe circuit is fine
It meansSuspect the computer last.
Symptoms
- Check engine light
- Engine stumbling, hesitating or surging (Honda)
- Difficulty refuelling (Nissan Frontier and Xterra)
How to fix
Step 1: Ask a dealer whether your VIN has an open bulletin or campaign for P1491.
Parts and cost context
- Engine control module (ECM / PCM):Test the EGR valve and wiring before replacing parts on a Honda. Labour varies; get a quote.
Labor varies by vehicle and shop; get a quote before you approve a repair.
Compare used part prices on PartPriceGuideOn your vehicle
HondaYour car
1995–2004 · Odyssey
Supported by vehicle dataHonda has EGR bulletins naming P1491: 090199 (1995-1996), warranty extension 00009 (1999-2003) and 012704 (2003-2004). Whether they are still current is not verified.
2003–2004 · Pilot
Supported by vehicle dataHonda warranty extension 00009 and bulletin 012704 name P1491 on the 2003-2004 Pilot. Whether they are still current is not verified.
1994–1996 · Accord
Supported by vehicle dataHonda 090199 covers troubleshooting P0401 and P1491 on the 1994-1996 Accord. Whether it is still current is not verified.
090199Status unverified
Troubleshooting EGR codes P0401 and P1491
1994–1996accord, odyssey · issued · NHTSA 608022
Information on troubleshooting the EGR diagnostic trouble codes. The NHTSA summary does not give the steps.
We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.
00009Status unverified
Warranty extension for EGR contamination (P0401, P1491)
1999–2003odyssey, pilot · issued · NHTSA 10017431
EGR valve contamination or port clogging may cause P0401, P1491 or hesitation and surge.
We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.
012704Status unverified
Request for visit, engine stumbling or surging
2003–2004pilot, odyssey · issued · NHTSA 10005652
Customer complaint of stumbling, shuddering, hesitation or surging, possibly with a check engine light and codes including P1491.
We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.
NissanYour car
2001–2002 · Frontier
Supported by vehicle dataNissan NTB01039 and NTB02017A cover a MIL with P1491 on the Frontier. Whether they are still current is not verified.
2001–2002 · Xterra
Supported by vehicle dataNissan NTB01039 and NTB02017A cover the Xterra as well. Whether they are still current is not verified.
NTB01039Status unverified
MIL on with P1491 and/or difficulty refuelling
2001frontier, xterra · issued · NHTSA 625200
The summary links the code to a refuelling problem and does not give the repair.
We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.
NTB02017AStatus unverified
MIL on with P1491 on some vehicles
2002frontier, xterra · issued · NHTSA 635792
The summary does not give the repair.
We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.
Related codes
Sources and review
- Honda 00009: warranty extension, EGR valve contamination or port clogging may cause P0401, P1491 or hesitation
- Honda service manual DTC troubleshooting: P1491 (12-3) EGR valve insufficient lift
- Honda 090199: troubleshooting EGR codes P0401 and P1491
- Nissan ITB02015: aid to diagnosing P1491 (vacuum cut valve bypass valve)
- Nissan NTB01039: MIL on with P1491 and/or difficulty refuelling
- Honda 012704: request for visit, engine stumbling or surging, check engine light and codes
- Nissan NTB02017A: MIL on with P1491 set on some vehicles
- NHTSA complaint ODI 10169787, 2000 Nissan Sentra
- NHTSA complaint ODI 10182110, 1999 Honda Accord
- Last reviewed
- 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