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DTC codes / P26xx · Computer and output circuits / P2668

P2668Fuel Mode Indicator Lamp Control Circuit

P2668 indicates that the powertrain control module has detected a fault in the electrical circuit that controls the fuel mode indicator lamp, which is the dash light that tells the driver when the engine is operating in a non-standard fuel mode such as a dedicated alternative-fuel strategy. The computer monitors the control circuit for expected voltage or current behavior and sets this code when the circuit does not respond as commanded, which usually points to a wiring, connection, or lamp assembly problem rather than an engine performance issue.

SystemPowertrain
Code typeGeneric (all makes)
SeverityLow
Fix difficultyIntermediate
AreaComputer and output circuits

Symptoms you may notice

  • The fuel mode indicator lamp fails to illuminate when the ignition is switched on or when the vehicle enters the alternative fuel mode.
  • The fuel mode indicator lamp stays illuminated continuously regardless of the actual fuel mode.
  • The check engine light is illuminated with no other noticeable driveability complaints.
  • Often no symptoms besides the warning light, because the lamp circuit does not affect how the engine runs.
  • In some vehicles, a message or icon related to fuel mode appears in the driver information center.
  • Intermittent lamp operation that changes with temperature, vibration, or moisture.

Common causes, most likely first

  1. A failed fuel mode indicator lamp bulb, LED, or lamp assembly.
  2. Corroded, loose, or damaged electrical connector at the lamp, the instrument cluster, or the powertrain control module.
  3. An open or shorted wire in the control circuit between the powertrain control module and the lamp.
  4. A faulty powertrain control module driver circuit, though this is less common than wiring and lamp faults.
  5. Water intrusion or physical damage to the harness that carries the lamp control circuit.
  6. A poor ground connection shared by the instrument cluster or lamp circuit.

How to diagnose and fix it

  1. Verify the fuel mode indicator lamp actually fails to illuminate by commanding it on with a scan tool and observing the dash; if it works, the fault may be intermittent and stored from a past event.
  2. Inspect the lamp bulb or LED and the instrument cluster connector for corrosion, looseness, or damage, replacing the lamp if it is open.
  3. Check the control circuit wiring for continuity and shorts between the powertrain control module and the lamp, repairing any damaged wire or connector.
  4. Measure voltage and resistance on the control circuit at the powertrain control module while commanding the lamp on and off to confirm the module is driving the circuit correctly.
  5. Check the ground circuit for the lamp or instrument cluster and clean or repair any poor ground connection.
  6. If the circuit and lamp are good but the powertrain control module does not command the lamp, diagnose the module and its programming before replacement.
  7. Clear the code and perform a road test or lamp command test to confirm the repair and ensure the code does not return.

What the fuel mode lamp circuit really means

  • This code is almost never an engine performance fault, so chasing fuel system or injector problems will waste time and money.
  • Many vehicles use the same lamp for multiple fuel modes, and a lamp that works in one mode but not another can point to a module configuration or software issue rather than a bad bulb.
  • A stored P2668 can be set by a brief voltage spike or a low battery during cranking, so check for a history of electrical system problems before condemning parts.
  • Aftermarket accessories tapped into the instrument cluster wiring are a common cause of lamp circuit faults that do not appear on a wiring diagram.
  • On some vehicles the fuel mode indicator is part of a larger cluster assembly, and a single failed lamp driver inside the cluster can set this code without any visible wiring damage.

Can I keep driving with P2668?

This code does not affect engine operation or safety, so the vehicle can be driven normally while you arrange diagnosis and repair. Avoid ignoring it indefinitely, because a lamp circuit fault can mask a genuine fuel mode problem if the driver relies on the indicator.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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