OBD Alternative Fuel Tank Select Valve C Control Circuit/Open
What it means
P2A99 stands for Alternative Fuel Tank Select Valve C Control Circuit/Open. P2A99 is a P code, so the fault sits in the engine, transmission and emissions systems. For P2A99, work through the cause list below, cheapest checks first.
Where it lives
For P2A99, the valve sits on the circuit this code reports. The description of P2A99 reports the valve as open.
What to check first
For P2A99, pull the connector and inspect the terminals for spread, corrosion or backed-out pins before testing anything else.
Check these first
- P2A99: Faulty or contaminated sensor in the fuel/air metering circuit
- P2A99: Damaged or shorted wiring or connector for the affected circuit
- P2A99: Vacuum leak or intake system restriction
- P2A99: Failing fuel pump, injector, or fuel pressure regulator
What to do next
P2A99 is a fault in the powertrain control system. The steps below are general, so what actually failed on your vehicle may not be what P2A99 names.
- P2A99: Read freeze frame data and related codes with an OBD-II scanner
- P2A99: Inspect the affected sensor wiring and connector for damage
- P2A99: Compare live sensor readings (fuel trim, airflow, temperatures) to manufacturer specs
- P2A99: Smoke test the intake system if lean or vacuum conditions are suspected
- P2A99: Replace the failed component after confirming it with live data
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Updated
Generic SAE J2012 definition. Last updated 2026-08-30.