What it means
The control circuit of alternative fuel tank shutoff valve B reports a control circuit high condition. Tank isolation cannot be commanded as expected on multi-tank CNG/LPG systems.
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 shutoff valve B isolates its tank on a multi-tank CNG or LPG system. The control module sets this code when the valve B circuit signal is above its expected range, commonly because the control wire is shorted to battery voltage or the valve coil is open.
Common causes
Most likely first.
- Control wire shorted to B+
- Open valve coil
- Connector pins corroded - high contact resistance
Symptoms
- Check-engine light
- Alternative-fuel warning light
- Difficulty switching fuel modes
How to diagnose it
- Save freeze-frame data and review valve B command and status data to confirm when the high-circuit condition occurs.
- Inspect valve B's connector and wiring for damage, loose terminals, or contact with a powered wire.
- Use the wiring diagram to test the valve B control wire for a short to battery voltage, following the manufacturer's isolation procedure.
- Check the valve B coil for an open circuit and inspect terminals for corrosion or high resistance using the manufacturer's specification.
- If wiring and coil tests pass, verify the control module output and feedback path using the manufacturer's procedure.
Common fixes
- Repair a valve B control wire shorted to battery voltage.
- Repair loose or corroded valve B connector terminals.
- Replace the valve B coil if it is confirmed open.
- Repair damaged wiring or a failed control-side connection found during testing.
Can I keep driving?
Avoid switching fuel modes repeatedly, and use only a mode the vehicle indicates is available and can isolate reliably. If tank B cannot be shut off as commanded, stop using the alternative-fuel system until the circuit fault is resolved.
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.