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 Altima · 1998–2001
On the second-generation Altima the vacuum cut valve bypass solenoid lives just inside the rear wheel well, beside the fuel tank and the spare tire well, bolted to a small steel bracket under the body. It is one of the most rust-exposed electrical components on the car, and in the salt belt the bracket assembly typically corrodes badly — owners in the Northeast describe having to soak the fasteners for a day before the bolts will come out without snapping. The solenoid is normally closed and opens only when the ECM grounds it to admit intake manifold vacuum to the fuel tank for the on-board EVAP leak diagnostic. P1490 is the circuit-side complaint: the ECM drove the valve and the electrical feedback was wrong, which on this car is nearly always either a dead solenoid coil or a corroded connector, not a leak. The companion code P1491 is set when the valve is electrically fine but the tank does not respond to the test, so which of the two codes you have narrows the search considerably before you touch anything. Drivers notice essentially nothing beyond the check engine light — no stumble, no hard start, no smell of fuel — and the car will drive indefinitely with the code present. The consequence is an emissions failure and a MIL that hides any more serious code that might follow, and because the EVAP monitor only runs under specific fuel-level and temperature conditions, clearing the code buys a few days of a dark dash before it returns.
Common Symptoms
- Check engine light on, car drives normally
- Solenoid does not click when 12V is applied at the terminals
- Heavily rusted bracket and hardware at the rear of the car
- Emissions inspection failure
- Code reappears within days of being cleared
How to Fix
The diagnostic that settles this takes ten minutes. Jack the rear of the car, find the solenoid just inside the wheel well next to the tank, and unplug it. Apply battery voltage directly across the two terminals: a good valve clicks audibly and you can feel or hear the air passage open, and it should close again the instant power is removed. If there is no click, the solenoid is dead and needs replacing. If it clicks properly, put the meter on the harness instead — check for continuity from the solenoid connector back to the ECM, check the ground, and inspect the connector for the green corrosion and water intrusion that is endemic at this location. Cleaning the pins and sealing the connector with dielectric grease resolves a meaningful share of these without any parts at all. When the valve itself is bad, the part is the Nissan 14933-54U0A cut valve solenoid shared across Altima, Maxima and Pathfinder of this era; owners have sourced good used units for well under $50, and aftermarket replacements are widely available, while the genuine Nissan part runs considerably more. Before you start, soak the bracket bolts with penetrating oil the day before — rusted-in hardware, not the valve, is what turns this into a long job. Replace the short rubber hoses at the valve while you are there, since they crack at this age. Clear the code afterward and drive the car through a proper cold-start-plus-cruise cycle with a partly filled tank so the EVAP monitor can run and set to ready.
Sources for this issue (4)
- Check/Replace the Vacuum Cut Valve Bypass Valve on a 1998-2001 Nissan Altimaarticle
- P1490 - Vacuum cut valve bypass valve (circuit) - NissanHelp Altima Forumforum
- Code P1490 Nissan - Vacuum Cut Valve Bypass Valvearticle
- Genuine Nissan 14933-54U0A Cut Valve Solenoid (Altima / Maxima / Pathfinder)manufacturer
Nissan Frontier · 2000–2004
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.