What does it mean?
This code is a generic powertrain code. It is considered generic because it applies to all makes and models of vehicles (1996 and newer), although specific repair steps may vary by model.
The Powertrain Control Module (PCM) has detected that the circuit is shorted together that controls the vent valve or solenoid for the vapor of the evaporative emission systems. In this case, the code will also be triggered when the valve is stuck closed.
When fuel is in the tank, it emits fuel vapor, while the vent line opens and allows the vapors to flow into the engine intake manifold, a charcoal canister, or into the atmosphere, depending on the vehicle. This purge valve is part of the simple yet complicated evaporative emissions system.
Symptoms
Symptoms of a DTC P0448 will include the illumination of the Malfunction Indicator Light (MIL), you will likely not notice any other symptoms.
Causes
Potential causes may include:
Faulty vent valve
Wiring/circuit issue
PCM fault
Possible Solutions
Here are some steps to follow to diagnose and repair this fault code:
Check your fuses, there may be a fuse that powers the vent solenoid.
Look for a rubbed or chafed wiring harness. Check both wires to see if they are shorted to each other, to ground, or to power.
Visually inspect the vent valve for cracks or damage.
Trace the wires to and from the PCM and check for continuity using a digital volt-ohm meter (DVOM).
If you have access to an advanced-level scan tool, activate the valve while reading the power and ground at the connector or simply using a test light wired to both terminals, it will light up if power and ground are OK.
Using a DVOM, check the resistance of the vent, in most cases the resistance reading should be low, refer to manufacturer specifications or compare it to a new one. A value too high or too low indicates a faulty coil inside the valve, thus meaning a replacement is necessary. This code seems to be widespread on Dodge, Chrysler, and Jeep products. In these cases, the vent valve was faulty. With GM products (especially trucks), GM released a new updated valve assembly.
Finally, remove the valve, you may be able to access the pivot inside and it might just be sticking due to fuel residue. Clean it and retest.
Other EVAP DTCs: P0440 – P0441 – P0442 – P0443 – P0444 – P0445 – P0446 – P0447 – P0449 – P0452 – P0453 – P0455 – P0456