P0650 — Malfunction Indicator Lamp (MIL) Control Circuit

Causes

• Open or short in MIL lamp wiring (to battery or ground)
• Faulty instrument cluster or MIL lamp/bulb/LED
• Loose, corroded, or damaged connectors or pins at the cluster or PCM
• Blown fuse or relay in the instrument lighting/ECM power circuit
• PCM/ECM internal driver failure or poor PCB solder joint
• Aftermarket installations (alarms, radios) tapping MIL circuit

Symptoms

• Check Engine MIL illuminated continuously or not operating as expected
• MIL fails to illuminate on key-on engine-off (KOEO) bulb check
• Intermittent MIL operation (flicker / on-only sometimes)
• Possible stored ECM/PCM communication or lamp control related codes

What to check

• Read and record all stored codes and freeze-frame data; note when code sets
• Verify MIL behavior: does lamp illuminate on key-on (bulb check)?
• Visual inspection of instrument cluster, harnesses and connectors for damage/corrosion
• Check relevant fuses and power/ground circuits for the cluster and ECM
• Backprobe the MIL control pin at the PCM and at the cluster while performing KOEO test
• Measure continuity and resistance between PCM MIL pin and cluster MIL lamp terminal

Signal parameters

• Key ON, Engine OFF (KOEO): MIL should perform a brief bulb-check (lamp lights briefly) — MIL control output may be driven or released depending on design
• With MIL commanded ON by PCM: control output typically switches to ground or battery depending on vehicle (expect ~0 V if switched to ground, or ~12 V if switched to supply)
• With MIL commanded OFF: circuit should be open/high impedance (battery voltage at lamp side if pulled up) or stable at supply voltage
• If PCM pulses MIL for flashing, expect a pulsed duty signal rather than a steady state
• Normal lamp load: low resistance when bulb present; an open circuit indicates bulb/LED failure or wiring open

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