Error Code is defined as P0448 is defined as Evaporative Emission Control System Vent Valve/Solenoid Circuit Shorted. Meaning, there’s a malfunctioning component in the EVAP control system, which is likely caused by improperly installed fuel cap, faulty purge control solenoid, defects on the hoses and/or vacuums, faulty pressure or flow sensor.

This code is a generic trouble code, meaning it applies to all vehicles equipped with OBD-II, especially made since 1996 up to present. Specifications on the definition, troubleshooting and repairs of course, vary from one make and/or model to another.

Definition

The EVAP system is part of the engine’s emission system, and this includes multiple components, such as the fuel cap, fuel lines, fuel pressure, charcoal canister, purge valve, flow sensors, connectors, electrical wirings, vacuum lines, vapor hoses and fuel tank. As the fuel sits inside the tank, it lets fuel vapor out, while simultaneously driving the vents open, allowing vapors to circulate to the engine intake manifold, a charcoal canister or into the atmosphere, depending on the vehicle

The Error Code P0448 takes place when there’s an abnormal reading from EVAP sensor that is not in compliance with the parameters set by the manufacturer’s reference voltage.

This code means the PCM (powertrain control module, also known as ECM or engine control module), has detected a short condition within the circuit which controls the vent valve or solenoid for evaporative emission system vapor.

Common Symptoms

Unlike most error codes, Error Code P0448 doesn’t usually show noticeable symptoms other than the illumination of the Check Engine light. However, the fault code is enough to cause the vehicle to fail emission inspection. However, other EVAP-related codes may be present.

Possible Causes

There are multiple factors that leads to this error code, some of the most common possible causes are:

  • Loose or defective cap
  • Defective purge control solenoid
  • Broken or cracked fuel vapor hoses
  • Broken or clogged charcoal canister
  • Broken or cracked vacuum lines
  • Faulty flow sensor
  • Faulty pressure sensor

How to Check

Technicians usually use a code reader or scanner, DVOM (digital volt/ohmmeter) and smoke machine to conduct a thorough diagnosis for this error code.

They start by conducting a visual inspection of all connectors and wirings involved in the EVAP. They will look for signs of rubbed-through wires or chafed wiring harness. They will check both wires to see if they are open to each other, to ground or power.

They check the fuse, as there may be a fuse that powers the vent solenoid. Next, they inspect the vent valve for signs of damage, such as cracks.

They connect the code reader to the diagnostic connector, record stored codes as well as the freeze frame data. They, they clear the codes, and take the vehicle for test drive to see if it comes back.

Then, they remove and reinstall the fuel cap to see if the code returns.

If the fuel cap is good but the code still returns, then technicians will proceed on checking the vacuum system and fuel vapor to look for signs of breakage, cracks, kinks and split. They will conduct repair as needed.

Using the DVOM, they trace the wires’ continuity to and from the PCM.

Also using the DVOM, they will check the vent’s resistance, in most cases, the reading should be low. You can refer to the specifications from the manufacturer, or simple compare it to a new one. Values that are too high or too low, easily indicates fault coil inside the valve, which means it needs to be replacement.

To detect vacuum leaks, they place the nozzle of the smoke machine close to the vacuum supply hose for the purge solenoid and fill the system with smoke. Then they look for smoke escaping from the lines. Faulty gas cap is a common issue, so watch the area around the fuel cap closely. Also, remember that the vent of the charcoal canister will allow smoke to go out slowly, which is completely normal.

Charcoal canisters can be contaminated, causing it to clog and restrict purge flow from the canister. With the purge control solenoid open, check for suction at both sides of the canister. If there are no suctions, then that means the canister is the problem. Remove it and shake it. Listen for broken, loose particles or anything that rattles. Replace as needed.

If the canister is working normally, then the check the fuel vapor hoses for crushed areas or kinks. If the lines are normal, test the operation of the purge control solenoid. It should work as on/off valve, as it completes a circuit that usually runs on battery voltage. Refer to the manufacturer’s spec before applying voltage.

If you have faulty solenoid, the EVP control circuit code will be present. If that is the case, then check the electrical connectors and look for signs of corrosion and damage. Repair as needed.

If wiring connectors are in good shape, unplug the connector from the PCM and conduct a resistance test on the wiring, system pressure and flow sensors and purge control solenoid. Compare results to the manufacturer’s specs. Repair as needed.

How to Fix

As you can see above, there are a lot of steps to conduct a thorough diagnosis for this error. But they’re all needed to fix the problem. To summarize the fix for this error code, the available options are:

  • Repair or replace fuel cap
  • Repair or replace charcoal canister
  • Repair or replace vacuum lines and hoses
  • Repair or replace purge control solenoid
  • Repair or replace fuel flow and pressure sensors

Though this code may not cause drivability issues, it will cause the vehicle to fail emission test, and emit excessive hydrocarbon fumes, which are harmful for the environment.