P2668

Code

Generic P — Powertrain

Fuel Mode Indicator Lamp Control Circuit

Brand: Generic

Type: P — Powertrain

Views: UK: 16 EN: 32 RU: 18

AI status

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Page language: EN

Causes

Open or short in the wiring harness to the fuel mode indicator lamp
Corroded, loose or damaged connector at the lamp or instrument cluster
Burned out bulb or failed LED module in the indicator
Faulty instrument cluster or lamp driver electronics
PCM/ECM output driver failure
Blown fuse or poor battery/ground connection

Symptoms

Fuel Mode Indicator lamp does not illuminate when expected
Lamp remains on constantly or flickers/intermittently
Inconsistent fuel mode indication to driver
Possible MIL (Check Engine) illumination
No drivability symptoms in many cases (electrical indicator only)

What to check

Scan for stored codes and freeze frame data; note if code is current or historic
Visual inspection of lamp, connector, wiring harness, and grommets for damage or corrosion
Check fuses and battery/ground connections related to instrument cluster
Operate the indicator lamp (if possible) while back-probing the connector to observe signal behavior
Measure continuity and resistance between lamp connector and PCM/cluster connector
Wiggle test harness while observing lamp behavior and scan tool data

Signal parameters

Control output expected to switch between ~0 V (driver low) and battery voltage (~11–14.5 V) when commanded on/off
Open circuit: infinite or very high resistance between lamp and driver (>1 kΩ)
Good lamp continuity: low resistance when removed/bench-tested (typical LED modules
Intermittent: voltage or continuity appears/disappears with movement or vibration
If driver is low-side type, expect ~0 V to lamp when ON and battery voltage at lamp feed; if high-side type, driver will supply battery voltage when ON

Diagnostic algorithm

Read and record codes, freeze frame and mode-status with a scan tool. Verify P2668 and any related codes.
Perform a visual inspection of the indicator lamp, instrument cluster connectors and wiring for damage, corrosion, water ingress, or aftermarket taps.
Confirm fuse(s) and general dash power/ground integrity. Repair any poor grounds.
Verify the lamp itself: remove the lamp/LED module and bench-test with a known good 12 V source (observe polarity and current limits for LEDs). Replace if faulty.
Back-probe the lamp connector with the ignition ON and command lamp ON (if possible) while monitoring voltage. Note whether the driver switches as expected.
Check continuity between the lamp connector and the PCM/cluster connector. Repair open circuits and damaged wires.

Likely causes

Broken/chewed wire or damaged insulation at harness near lamp or bulkhead
Loose or corroded connector at instrument cluster or lamp assembly
Failed lamp/LED (open circuit or shorted module)
Faulty lamp driver inside the instrument cluster
PCM/ECM driver transistor weak or shorted

Fault status

⚠️ Status

Control circuit fault detected for Fuel Mode Indicator Lamp — open/short/driver failure. Lamp not responding within expected voltage/current parameters.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours