What it means
The alternative fuel control module reports a system voltage out of operating range. CNG, LPG, or hydrogen fuelling can be disabled until voltage is in spec.
At a glance
- Usually lights the check-engine light
How it works
The alternative-fuel control module checks whether its supply voltage is within the range needed to manage CNG, LPG, or hydrogen operation. This code sets when the module reports voltage outside that range, so it may disable alternative-fuel operation until voltage recovers.
Common causes
Most likely first.
- Weak battery sags voltage under load
- Alternator output out of regulation
Symptoms
- Check-engine or alternative-fuel system warning light may come on
- Alternative-fuel operation may be unavailable
- Vehicle may switch to another available fuel, depending on the system
How to diagnose it
- Use a scan tool to record freeze-frame data and check system voltage when P26EB was set, since the fault may occur only during cranking or under electrical load.
- Check the battery terminals, grounds, and charging-system connections for looseness, corrosion, or damage that could cause voltage drop.
- Test battery condition and voltage during starting and under load against the manufacturer's specification.
- Measure charging-system output at idle and with electrical loads on, and compare it with the manufacturer's specification.
- If battery and alternator tests pass, check power and ground at the alternative-fuel control module while the fault is present.
Common fixes
- Clean and secure corroded or loose battery terminals and grounds.
- Charge or replace a weak battery after confirming its condition.
- Repair a damaged charging-system connection or ground.
- Repair or replace the alternator if its regulated output is outside specification.
Can I keep driving?
If the vehicle runs normally on another available fuel, a short trip may be possible, but alternative-fuel operation may remain disabled. Avoid relying on CNG, LPG, or hydrogen range until the voltage fault is repaired; if the vehicle stalls, displays a temperature or electrical warning, or will not start reliably, stop driving.
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.