P1490 on Infiniti: How to Diagnose & Fix
Secondary Air Relief / Injection Solenoid Circuit Malfunction
1 Infiniti model · 1 documented issue · $90-$400 repair
On Infiniti vehicles, P1490 (secondary air relief / injection solenoid circuit malfunction) is most often reported on the 1997-2003 Infiniti QX4 as EVAP Bypass Solenoid Under the Floor Pan Clogs and Sets a Persistent MIL ($90-$400 repair). 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. Each section below gives the symptoms, how to confirm the cause, the fix, parts and sources for that model.
Common causes of P1490 (all vehicles)
- 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)
P1490 on Infiniti by model: symptoms, diagnosis and fix
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.
Looking for P1490 on a different make?
View P1490 across all makes →Frequently asked questions
What does P1490 mean on a Infiniti?
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. On Infiniti it is documented across 1 model: QX4.
How do I diagnose P1490 on a Infiniti QX4?
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. Published repair guidance and available estimates are in the QX4 section on this page.
What causes P1490 on Infiniti vehicles?
Documented causes on Infiniti: EVAP Bypass Solenoid Under the Floor Pan Clogs and Sets a Persistent MIL. Generic causes of P1490: 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.
How much does it cost to fix P1490 on a Infiniti?
Published repair estimates on Infiniti range from $90 to $400 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.