What it means
The control circuit of alternative fuel tank shutoff valve B reports a control circuit low 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 controls isolation of its tank on a multi-tank CNG or LPG system. The control module sets this code when the valve B circuit signal is below its expected range, which can result from a short to ground, a shorted coil, or high resistance at a corroded connection.
Common causes
Most likely first.
- Control wire shorted to ground
- Internal short in valve coil
- Connector pins corroded - high contact resistance
Symptoms
- Check-engine light
- Alternative-fuel warning light
- Difficulty switching fuel modes
How to diagnose it
- Record freeze-frame data and review valve B command and status data to confirm when the low-circuit condition occurs.
- Inspect valve B's connector and wiring for corrosion, damaged insulation, or a wire touching ground.
- Check connector terminals for corrosion or weak contact, since added resistance can pull the circuit signal low.
- Use the wiring diagram to test the valve B control wire for a short to ground and check the coil against the manufacturer's specification.
- If the valve circuit passes, verify the control module output and its ground or supply connections using the manufacturer's procedure.
Common fixes
- Clean or replace corroded valve B connector terminals.
- Repair a valve B control wire shorted to ground.
- Repair damaged wiring or a poor ground connection.
- Replace the valve B coil if testing confirms an internal short.
Can I keep driving?
Use only a fuel mode the vehicle can select and isolate reliably, and avoid repeated mode changes. If tank B cannot be shut off as commanded, stop using the alternative-fuel system until it is checked.
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.