P0448
EVAP System Vent Control Circuit Shorted.
- Generic
- Powertrain
- Generic code
- Low severity
How this code is built
- P
- SystemPowertrain
- 0
- Defined bySAE, the same on every car
- 4
- AreaAuxiliary emission controls
- 48
- FaultThe specific fault in that area
What it means
P0448 means the engine control unit has detected that the EVAP vent control circuit is shorted. The vent valve normally sits between the charcoal canister and fresh air and is closed during leak tests. The control unit saw a voltage or current on the valve's control circuit that matched a short, such as a short to power or an overloaded driver, and set the code.
Symptoms
- Engine warning light on
- Difficulty refuelling, with the pump clicking off repeatedly
- Fuel smell around the rear of the car
- Failed emissions or MOT test
- Evaporative monitor showing not ready
- Usually no change in how the engine drives
Possible causes
- Faulty EVAP vent valve with an internal short in the solenoid coillikely
- Damaged, chafed or corroded wiring to the vent valve, shorting to power or groundlikely
- Water, dirt or corrosion in the vent valve connectorpossible
- Vent valve damaged by water ingress or physical impact near the canisterpossible
- Faulty driver circuit inside the engine control unitrare
- Previous repair or accident damage to the loom near the fuel tank or canisterrare
How to diagnose
- Read the stored codes and freeze frame data, and note any other EVAP codes and when the fault set
- Locate the vent valve, which is usually near the canister or fuel tank (position varies by model), and inspect its housing, connector and wiring for damage, water and corrosion
- Check the connector pins for green corrosion, bent terminals or poor tension
- Measure the valve coil resistance and compare it with the manufacturer's specification for that model
- Use a diagnostic scan tool to command the vent valve on and off and listen or feel for it clicking
- Check the supply and control wires for shorts to power or ground with the connector unplugged, following the wiring diagram for the vehicle
- Check the valve's power supply and fuse where fitted
- If the valve and wiring test good, check the control unit's driver output before suspecting the control unit itself
How to fix
- Replace the vent valve if the coil is shorted or the valve will not operate
- Repair or replace chafed or shorted wiring and secure it away from sharp edges and heat
- Clean or replace a corroded connector and its terminals, then seal it against water
- Replace a vent valve that has been damaged by water or impact and find out how the water or damage got there
- Repair or replace the control unit only after the wiring and valve have been proven good
- Clear the code after repair and run the evaporative monitor drive cycle to confirm it passes
Can I keep driving?
Low severity
The car is normally safe to drive, as this fault rarely affects how it runs. Book it in soon, particularly if you notice a fuel smell or need an emissions test.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.