On bi-fuel engines a separate alternative fuel control module often runs the gas side. In Ford's bi-fuel CNG documentation of 2002 it contains drivers for both injector sets, switches the fuel relays, picks the active fuel from the selector switch and shuts the tank valve when gas pressure falls below 517 kPa. In Roush CleanTech's propane systems for Ford trucks a smart relay module takes on that role and talks to the PCM over CAN. P26EB says the supply voltage measured by or at this module is outside its permitted window, from a weak feed, a bad ground or a charging fault. No manufacturer documents P26EB publicly. CARB requires an approved monitoring plan for alternate-fuel vehicles. The vehicle will usually refuse or drop gas mode and continue on gasoline.
High severity. Can I keep driving?If you smell gas, do not keep driving or start the engine: move away and call for assistance. With no smell, drive moderately to an authorized shop.
Symptoms
- Gas mode not available or vehicle switches back to gasoline
- Fuel mode indicator flashes or shows a fault
- Warning light on
Most likely causes
- Loose, corroded or undersized power or ground connection at the gas control module
- Faulty fuse, relay or feed circuit of the gas system
- Weak battery or alternator voltage outside the normal range
- Internal fault in the alternative fuel control module
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: medium
- It affects emissions.
What each character of P26EB means
- P: Powertrain: engine and transmission
- 2: Generic code: same on every make
- 6: Control modules and outputs
- EB: Specific fault in that system
Frequently asked questions
Can I keep driving with code P26EB?
If you smell gas, do not keep driving or start the engine: move away and call for assistance. With no smell, drive moderately to an authorized shop.
What causes code P26EB?
The most common causes are: loose, corroded or undersized power or ground connection at the gas control module; faulty fuse, relay or feed circuit of the gas system; weak battery or alternator voltage outside the normal range.
Related codes
- P0618Alternative Fuel Control Module KAM Error
- P0562System Voltage Low
- P0563System Voltage High
- P25BEAlternative Fuel Disable Control Circuit/Open
- P26E2Fuel Mode Indicator Lamp Control Circuit Low
Sources
- static.nhtsa.gov: INRD PE08063 33504P
- roushcleantech.com: Roush CleanTech Diagnostics Manual DA 8.5.18
- law.cornell.edu: 13 CCR 1968.2
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.