P2A99: Alternative Fuel Tank Select Valve C Control Circuit/Open

What it means

The alternative fuel tank select valve C control circuit is open or has a fault.

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

Alternative-fuel tank-select valve C has a control circuit that lets the module command tank selection. This code sets when the valve C circuit is open or otherwise fails to complete the commanded electrical path, including an open wire, open coil, or connector pin pushed out of place.

Common causes

Most likely first.

1. Open in valve control wire
2. Open valve coil
3. Pin pushed back out of connector body

Symptoms

• Check-engine or alternative-fuel system warning light, if equipped
• Difficulty switching fuel tanks
• Loss of power or stalling

How to diagnose it

1. Review freeze-frame data and live data to confirm valve C was commanded when the fault registered and note the selected tank.
2. Inspect valve C’s connector closely for a pin pushed back into the housing, incomplete latching, or corrosion.
3. Trace valve C’s control wire for a break, chafing, or a disconnected section, paying attention to harness bends and connector entry points.
4. Test the valve C coil and control wire for continuity using the wiring diagram and the manufacturer’s procedure.
5. If wiring and coil continuity are intact, check the module connector and command response for an intermittent open.

Common fixes

• Seat the pushed-back pin and secure the valve C connector.
• Repair an open or damaged valve C control wire.
• Replace valve C if its coil is open.
• Clear the code and confirm valve C can be commanded through a tank-selection cycle.

Can I keep driving?

An open valve C circuit can prevent selection of the tank that depends on that valve and may cause poor running or stalling. Avoid driving if power delivery is erratic or the vehicle stalls.