P1490 Code on Nissan or Subaru? Why Your $50 Scanner Can’t Fix It

Check Engine Light on? Scanner reading P1490? Don't panic, but don't just clear it and hope for the best. This isn't a generic misfire code—it's manufacturer-specific, and it means something totally different depending on what you drive.

The "P1490" Confusion

Most drivers panic when they see a code they can't immediately find on a basic Google search. Unlike a standard P0300 (Random Misfire), P1490 is a "Manufacturer Controlled Auxiliary Emission Controls" code. In plain English? It depends on the car.

🚗 If you drive a Nissan or Infiniti:

You are likely dealing with the Vacuum Cut Valve Bypass Valve (part of your EVAP system). Usually, it's a clog or a circuit failure. If you ignore it, you won't pass emissions.

🚙 If you drive a Subaru:

It’s often a Thermostat Function issue. Your car thinks the cooling fans or thermostat aren't reacting fast enough. This can lead to overheating if ignored.

Why "Reading" the Code Isn't Enough

Here’s the trap: A cheap dongle will tell you "P1490 exists." It won't tell you if the valve is stuck, if the wire is broken, or if the sensor is lying. To figure that out without firing the "parts cannon" (replacing parts randomly), you need a tool that can talk back to the car.

This is where the iCarsoft CR Ultra P separates itself from the budget tools. It features Bi-Directional Control (Active Test).

(By the way, we recently did a deep-dive review and video breakdown of the CR Ultra P's full capabilities. If you want to see this tool in action on a real vehicle, check out our full video review here.)

How to Diagnose P1490 Like a Pro

Using the CR Ultra P, you can skip the guesswork. Here is the workflow we recommend:

Hook Up & Auto Scan: Plug into the OBDII port. The CR Ultra P’s "Topology Map" will show you all modules. If you see P1490 in the ECM (Engine Control Module), tap it.
The "Active Test" (The Magic Step):
- For Nissan: Go to Actuation Test -> Vent Control Valve. Toggle it ON on the screen.
- Listen: Can you hear the valve clicking near the charcoal canister?
  - Yes? The valve is good; check your hoses for clogs.
  - No? The valve (or wiring) is dead. Replace it.
Verify the Fix: After replacing the part, don't just clear the code. Use the CR Ultra P to reset the ECU Self-Learning data. This stops the code from coming back instantly.

For more technical details on how OBD-II drive cycles work, this Wikipedia entry on OBD-II PIDs is a great resource for the geeks among us.

Common Questions

Q: Can I just clean the valve on my Nissan?: A: Sometimes. If it's just stuck with carbon buildup, some WD-40 might free it up. But given how hard it is to reach, most mechanics recommend swapping it out for a new one.
Q: Will P1490 put my car in "Limp Mode"?: A: Rarely. It's usually an emissions or sensor logic code. However, you will fail your state inspection immediately.