P0618 indicates a problem with the Alternative Fuel Control Module (AFCM) or its communication, often related to a malfunctioning or misaligned check valve that controls fuel flow for alternative fuels such as ethanol or gasoline blends.
The check valve that controls the flow of alternative fuel can become stuck or misaligned, preventing proper pressure regulation.
Corrosion, fraying, or a short in the sensor leads can disrupt the AFCM signal.
The AFCM itself can fail internally, losing its ability to regulate fuel flow.
Using fuel with improper ethanol content or contamination can trigger AFCM error codes.
Although rare, a fault in the engine control module’s communication with the AFCM can cause a P0618 code.
A common cause is a damaged or misaligned check valve, or wiring corrosion that disrupts the AFCM signal. Mechanical inspection should precede any electronic troubleshooting.
Replacing the PCM is generally unnecessary and rarely resolves this code. The issue is almost always mechanical or electrical in the AFCM circuit.
Fuel blends that contain incorrect ethanol percentages, contaminated ethanol, or non‑approved alternative fuels can cause AFCM errors.