What it means
The control circuit of the alternative fuel return line valve reports a control circuit low condition. Excess fuel return to the tank cannot be commanded as expected.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
- The engine or gearbox may go into limp mode
How it works
The alternative-fuel return-line valve regulates how much fuel returns to the tank, and its control circuit lets the module command the valve. The module sets P2AA0 when it detects a low electrical level in that circuit, which can prevent the valve from opening as commanded.
Common causes
Most likely first.
- Control wire shorted to ground
- Internal short in valve coil
- Connector pins corroded - high contact resistance
Symptoms
- Check-engine or alternative-fuel system warning light, if equipped
- Reduced power or poor acceleration
- Rough running or stalling
How to diagnose it
- Use a scan tool to record freeze-frame data and check alternative-fuel valve commands and related codes to see when the low-circuit fault occurs.
- With the system safely accessible, inspect the return-line valve connector and control-wire harness for corrosion, damage, or contact with ground.
- Check the connector pins for corrosion or poor contact, since added resistance can disrupt the valve control circuit.
- Test the control wire for a short to ground using the manufacturer's procedure and specification.
- Test the valve coil for an internal short and compare the result with the manufacturer's specification.
Common fixes
- Clean or repair corroded valve connector pins and restore a secure connection.
- Repair or replace the control wire where it is shorted to ground.
- Replace the return-line valve if its coil is internally shorted.
- Clear the code and verify that the valve responds to commands and the fault does not return.
Can I keep driving?
Avoid hard acceleration and extended driving if power is reduced or the engine runs roughly, since incorrect alternative-fuel return control can worsen drivability or cause stalling. Stop somewhere safe if it stalls or the warning indicates a fuel-system problem.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.