P1490: How to Diagnose & Fix — Secondary Air Relief / Injection Solenoid Circuit Malfunction
5 vehicles · 2 makes · $80-$600 repair
How to diagnose and fix P1490: most-reported vehicles
Ranked by owner reports. Each card gives the symptoms, how to confirm the cause, the fix, parts and sources for that vehicle.
Infiniti QX4 · 1997–2003
The QX4 is the R50 Pathfinder in a dinner jacket, and it inherits the same badly sited EVAP hardware: the vacuum cut valve and its bypass solenoid are mounted outside on a bracket under the floor pan, behind the driver's-side rear spring, not on top of the fuel tank where most owners go looking for them. Forum diagnosis of P1490 on these trucks — including a thread opened by a QX4 owner — identifies the pair visually, with the green unit the bypass solenoid and the white one the cut valve. The bypass solenoid is normally closed; the ECM grounds it only during the EVAP leak diagnostic so that intake manifold vacuum can be routed past the cut valve and applied to the tank. P1490 is raised when that drive does not produce the expected electrical response, so the suspects are the solenoid coil, the connector, and the harness run along the frame. In practice, on a vehicle of this age in any climate that uses road salt, the failure is corrosion at the connector or rust and debris packed into the valve body causing the plunger to hang. Because the valve does nothing during normal driving, the owner sees only a check engine light on an otherwise perfectly behaved truck; the practical damage is a failed inspection and the fact that the standing code masks whatever the VQ35DE or VG33E might report next. Because these solenoids are expensive through Infiniti, and because the fault is frequently mechanical fouling rather than a burned coil, the community consensus is to clean before condemning.
Common Symptoms
- Check engine light with no drivability symptoms
- Repeat P1490 after clearing
- EVAP readiness monitor never sets
- Bypass solenoid sticks or does not click when energized
- Corroded connector and seized bracket bolts under the rear floor pan
How to Fix
Get under the truck and locate the bracket behind the driver's rear spring — this is the single most common reason people fail to fix this code, because they search on top of the tank and give up. Unplug the green bypass solenoid and inspect the connector shell for standing water, corroded pins and a cracked seal. Then verify the valve: apply 12V across its terminals and confirm it clicks and opens the air passage between ports, and confirm it seals when power is removed; the factory test calls for the valve to switch in one second or less, and blowing through the ports with and without voltage is the quick field version. If the valve is sluggish or silent, disassemble it — it comes apart with basic hand tools — and clean the rust scale and grit out of the bore before spending money on a replacement, which is what experienced owners on the platform recommend given the part price. Inspect the cut valve (the white unit) and the short vacuum hoses between the two at the same time; cracked and hardened hoses and split plastic fittings are common and will keep the EVAP system failing even with a new solenoid. If the valve tests good, the fault is in the wiring: check continuity from the connector back to the ECM and look for chafe or rodent damage along the frame rail. Consult the factory service manual for the pin-out and resistance spec rather than guessing. Soak all bracket hardware in penetrating oil in advance, as the bolts are usually seized. After repair, clear the code and complete a full drive cycle with a partial fuel load so the EVAP monitor runs and confirms the repair instead of leaving the readiness flag unset at the inspection lane.
Sources for this issue (4)
- Loads of Codes - QX4 / 96-2004 R50 platform, P1490 vacuum cut valve bypass valve (NPORA Forums)forum
- P1490 Infiniti: Code Meaning, Causes, Symptoms, & Tech Notesarticle
- P1490 Vacuum Cut Valve Bypass Valve (Circuit) (Nissan, Infiniti) - Maxima Forumsforum
- Code P1490 - Vacuum Cut Valve Bypass Valvearticle
Nissan Xterra · 2000–2004
The first-generation Xterra carries the same rear-mounted EVAP vacuum cut valve and bypass solenoid as its Frontier and Pathfinder siblings, and it fails the same way — only more often, because the Xterra's buyers actually drove them through the mud, snow and gravel the mounting location is least able to survive. The assembly is visible through the rear passenger wheel well, sitting near the fuel tank on the EVAP purge line between the tank and the charcoal canister. The vacuum cut valve blocks intake manifold vacuum from reaching the tank in normal operation; the bypass valve is a normally closed solenoid the ECM grounds to deliberately route that vacuum to the tank when it wants to run the EVAP leak test. P1490 is set on the electrical side of that: the ECM has driven the solenoid and has not seen the expected circuit response, which points at the solenoid coil, its connector, or the wire between it and the ECM. Owners report the light appearing with the truck driving completely normally, which is what makes this code frustrating — there is nothing to feel, nothing to hear, and no reason to suspect a part hanging under the back of the truck. In salt-belt trucks the connector is often full of corrosion and the bracket hardware is rusted; in trucks that see off-road use the valve body itself is packed with grit. A less common but real variant on this platform: a broken or missing exhaust tailpipe section has been known to route hot gas near the valve and heat-damage the plastic body outright, and that heat damage can extend to melted wiring.
Common Symptoms
- Check engine light with no change in how the truck drives
- P1490 returns after clearing
- Emissions test failure or EVAP monitor not ready
- Solenoid does not click when energized on the bench
- Rusted bracket and corroded two-pin connector at the rear of the vehicle
How to Fix
Start under the truck at the rear passenger-side wheel well rather than in the engine bay. Disconnect the solenoid and inspect the connector — corroded, spread or backed-out pins are common and are a cheap fix. Bench-test the valve by applying battery voltage across its terminals: airflow should pass between ports A and B with voltage applied and stop cleanly when it is removed, with the transition happening in under a second. Blowing through the ports with and without power is the field version of that test. A valve that does not click, sticks partially open, or leaks with voltage removed should be replaced; a valve that clicks correctly but still sets the code means the problem lies in the harness or the ECM driver circuit, so ohm the wire from the solenoid connector back to the ECM and look for chafe points along the frame. Where the valve is merely clogged, it can be disassembled, cleaned of rust scale and debris, and reinstalled — a well-documented forum repair that saves the cost of the part. Inspect and replace the short rubber lines between the cut valve and bypass valve while access is open; they harden and split at this age and will set EVAP leak codes even after a good solenoid is fitted. Soak the bracket fasteners with penetrating oil before attempting removal. Finally, verify the exhaust behind the muffler is intact and not blowing on the valve, and check the nearby wiring for heat damage if it is not. Clear the code and complete a drive cycle with the tank between roughly a quarter and three-quarters full so the EVAP monitor can actually run and confirm the fix.
Sources for this issue (4)
Nissan Frontier · 2000–2004
The evaporative emissions system on these trucks commonly develops faults from a sticking vent control valve, saturated charcoal canister, cracked hoses, or rust/dirt intrusion near the rear-mounted canister. Owners frequently report persistent check-engine lights and failed emissions inspections even though the truck otherwise drives normally. Nissan published EVAP-related service bulletins for leak and vent valve diagnosis on Frontier/Xterra-era trucks.
Common Symptoms
- check engine light
- failed emissions test
- fuel smell near rear of truck
- no drivability symptoms
- intermittent EVAP leak code
How to Fix
Diagnosis should include smoke testing the EVAP system, checking the vent control valve operation, inspecting canister hoses and purge lines, and verifying the gas cap seals properly. Repairs range from replacing the vent valve or damaged hoses to replacing the charcoal canister assembly if fuel saturation or contamination is present, then clearing codes and completing a drive cycle.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Genuine Nissan EVAP purge control valve 14930-5M00A
2000-2004 Frontier 2.4L and 3.3L applications on the live fitment table; confirm VIN and current supersession.
- Genuine Nissan EVAP pressure/drain-cut valve 14935-5M00B
Confirm VIN.
- Genuine Nissan EVAP canister 14950-5S601
Confirm VIN.
- Standard Motor Products CP3090 carbon canister
Direct listing covers 2001-2003 Frontier 2.4L and 2004 through 07/01/2004; verify the exact production date and live application before purchase.
As an Amazon Associate, we earn from qualifying purchases; other part links may also earn au7o a commission. Confirm fitment by VIN before buying.
Owner tips & cautions
- TipBefore replacing the canister, test the gas cap and vent valve first; many owners solve the code with the valve or cracked hose rather than the full canister.
Sources for this issue (1)
Nissan Altima · 1998–2001
Nissan Pathfinder · 1998–2004
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P1490 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P1490 mean?
P1490 stands for "Secondary Air Relief / Injection Solenoid Circuit Malfunction." This is a manufacturer-specific code whose exact meaning varies by maker; on Ford it commonly indicates a fault in the secondary air relief solenoid circuit (part of the system that injects air into the exhaust to reduce cold-start emissions), while some applications use it for an EVAP or vacuum solenoid circuit. The computer detected that the solenoid circuit is open, shorted, or out of range. It is primarily an emissions-system fault and not an immediate drivability danger. Confirming the exact definition against the specific vehicle is recommended.
What are the most common causes of P1490?
The most common causes of P1490 are: Faulty secondary air (or vacuum) solenoid, Open or shorted wiring in the solenoid circuit, Corroded or loose electrical connector, Vacuum leak or collapsed vacuum hose, Failed secondary air pump or related relay, PCM driver circuit fault (less common). The specific cause varies by vehicle.
How much does it cost to fix P1490?
Repair costs for P1490 range from $80 to $600, depending on the vehicle and root cause.
Which vehicles are affected by P1490?
Au7o has documented P1490 across 5 vehicle models from 2 manufacturers: Infiniti, Nissan.
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Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.