What it means
The alternative fuel tank select valve B control circuit signal is lower than 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
Alternative-fuel tank-select valve B is operated through an electrical control circuit. The module monitors that circuit while commanding valve B; this code sets when the monitored signal is below its expected level, which can happen with a short to ground, a shorted coil, or a poor connector contact.
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
- Difficulty switching fuel tanks
- Loss of power or stalling
How to diagnose it
- Review freeze-frame data and live data to confirm the fault occurred while valve B was being commanded and note any tank-switching symptoms.
- Inspect valve B’s connector and harness for corrosion, rubbed-through insulation, or wiring touching ground.
- Check connector pin fit and corrosion, since added resistance can pull the valve B circuit signal low.
- With the circuit isolated as directed by the wiring diagram, check the valve B coil and control wire for a short to ground.
- Compare circuit readings with the manufacturer’s specification to distinguish a grounded wire from an internally shorted coil.
Common fixes
- Clean and secure corroded or loose valve B connector pins.
- Repair the valve B control wire if it is shorted to ground or damaged.
- Replace valve B if its coil is internally shorted.
- Clear the code and confirm the valve B circuit responds normally during a commanded tank switch.
Can I keep driving?
A low circuit signal can prevent valve B from switching tanks and may lead to power loss or stalling. Limit driving if the vehicle runs poorly, and avoid relying on tank selection until repaired.
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.