What does it mean?
P1209 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Generator 2 Control Circuit Short To Battery .
Symptoms
- Charge warning lamp and check engine lamp on together
- Battery overcharging or undercharging, sometimes with a hot or swollen battery
- Headlights brightening and dimming with engine speed
- System voltage collapses when high electrical loads are switched on
- Repeated battery failures over a short period
Likely causes
- Chafed control wire touching a permanent power feed or a battery stud inside the engine harness
- Corroded, melted or water filled connector at the second generator
- Internal short in the generator regulator holding the control line high
- Aftermarket equipment wired incorrectly into the charging harness
- Damaged control driver in the module that operates the generator
- A previous harness repair made with the wrong wire or a poor splice
How to fix it
- Measure system voltage at the battery at idle and at raised engine speed and note how each generator behaves
- Unplug the second generator and check the control wire for voltage with the ignition on; voltage there confirms the short
- Follow the harness along its route and look for chafe against brackets, the engine and battery cables
- Inspect the generator connector for melted plastic, corrosion and pushed-out terminals
- Disconnect any added accessories tapped into the charging system and retest
- Repair the wiring and retest before replacing the generator
- Replace the generator or its regulator only if the control line goes high solely with it connected