Bi-fuel vehicles tell the driver which fuel is in use through a small indicator, often built into the fuel selector button. On GM's 2016 Silverado and Sierra with CNG the light is off on gasoline, steady on natural gas, flashes once per second during a changeover and flashes about ten times per second when the CNG system has a fault; the 2015 Impala Bi-Fuel uses a similar light in its CNG switch. P2668 indicates that the module driving this lamp has found a fault in its control circuit, such as an open wire or a failed bulb or LED. No manufacturer documents the code publicly. Fuel switching itself is unaffected, but the driver loses the fuel mode display and the error warning. P26E2 and P26E3 are the low and high variants.
Low severity. Can I keep driving?You can normally keep driving. If it affects the fuel level, do not trust the gauge and refuel earlier than usual.
Symptoms
- Fuel mode lamp stays dark in gas mode
- No flashing during fuel changeover or on errors
Most likely causes
- Indicator LED or bulb in the selector switch failed
- Open wire or loose connector at the switch
- Lamp driver in the control module defective
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: easy
What each character of P2668 means
- P: Powertrain: engine and transmission
- 2: Generic code: same on every make
- 6: Control modules and outputs
- 68: Specific fault in that system
Frequently asked questions
Can I keep driving with code P2668?
You can normally keep driving. If it affects the fuel level, do not trust the gauge and refuel earlier than usual.
What causes code P2668?
The most common causes are: indicator LED or bulb in the selector switch failed; open wire or loose connector at the switch; lamp driver in the control module defective.
Related codes
- P26E2Fuel Mode Indicator Lamp Control Circuit Low
- P26E3Fuel Mode Indicator Lamp Control Circuit High
- P25A4Fuel Mode Select Switch Circuit
- P2665Fuel Shutoff Valve B Control Circuit/Open
Sources
Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.