P1800 is a manufacturer-specific trouble code. For Nissan-made automobiles, it indicates an issue with the variable intake air system (VIAS) control solenoid. It’s a widespread Nissan code.
This code is usually caused by a bad variable intake air system control solenoid.
Nissan P1800 Definition: VIAS Control Solenoid Valve Circuit
The variable intake air system changes the flow characteristics of the intake manifold. When it is off (which is the default), the intake manifold flows for efficiency. When VIAS is activated, the intake manifold flows for power.
The system is operated by a vacuum-controlled actuator. When vacuum flows into the VIAS actuator, the intake flow is changed to favor peak engine power. The VIAS control solenoid sits in the middle of this vacuum line and allows the ECM to send intake vacuum to the actuator.
When the powertrain control module (PCM) has detected an issue with the VIAS control solenoid, P1800 will be stored, and the check engine light will come on.
Nissan P1800 Symptoms
With the way the VIAS system works, it defaults to efficiency mode. When activated, the system changes the geometry inside the intake manifold to allow for a better high-end throttle response.
The vehicle will run and drive fine under 2000 RPM. Only when you ask for more power will you notice a lack of throttle response. It will not be a significant difference.
Other than that, the only symptom of P1800 should be the check engine light.
Nissan P1800 Causes + Diagnosis
The good news when fixing Nissan P1800 is that the VIAS solenoid and actuator are easy to see with most Nissan-made engines. The solenoid is usually bolted right to the top of the intake manifold. The actuator will be on the left side of the intake.
The most common repair for P1800 in a Nissan is a new VIAS control solenoid, but there are some diagnostic steps you can take that’ll keep you from getting a part you don’t need.
Test the Vacuum Lines
There will be a vacuum line coming from a reservoir to the VIAS control solenoid and another leaving it. Make sure that they aren’t broken, cracked, or otherwise leaking. If the VIAS control system can’t hold vacuum, it can’t activate.
Test the VIAS Control Actuator
Follow the vacuum line from the VIAS control solenoid. At the end of it, you’ll find the actuator. Gently pull it toward you to verify that it is still moving freely. If there’s no movement at all, the system could be bound.
Use a Scan Tool To Command the VIAS On
Unfortunately, the only way to get the VIAS control solenoid to activate is to increase the engine load at speed, which you can’t do in your driveway. However, a good scan tool can activate it with the push of a button.
- Make sure that there is vacuum going to the VIAS control solenoid.
- Use the scan tool to command the VIAS control solenoid to turn on.
- You should see the actuator move. If it doesn’t, and you want to be 100% certain, take the vacuum line that goes to the actuator off and put your finger over the hole. You should feel no vacuum with it off and vacuum with it on.
- If there’s no vacuum with it on, confirm the VIAS control solenoid is getting voltage. If it’s getting voltage, it needs to be replaced. If there’s no voltage, you’ll need to figure out where the wiring issue is.
A good scan tool can make pretty short work of diagnosing P1800 in your Nissan. If you don’t have one, a new VIAS control solenoid is usually around $20 at the local parts store, which is much cheaper than a good scanner. It’s not a big gamble to throw it in there and see if that clears the code.