What does it mean?
P1291 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Injector High Side Short To GND Or VBATT (Bank 1) .
Symptoms
- MIL (check engine lamp) on, often flashing
- Hard starting or a complete no-start
- Heavy misfire on Bank 1, rough idle and strong vibration
- Engine effectively running on one bank only, with severe power loss
- Blown injector fuse, fuel smell or black smoke if an injector is held open
Likely causes
- Bank 1 injector harness chafed against the valve cover, a bracket or the intake
- Fuel or oil soaked harness with degraded insulation under the valve cover
- Internally shorted injector solenoid on Bank 1
- Water and corrosion in an injector connector or at a harness pass-through
- Damaged pins or a shorted output in the injector driver module
- Wiring pinched during earlier intake manifold or valve cover work
How to fix it
- Read the freeze frame and use live misfire counters to see which cylinders are down
- Disconnect Bank 1 injectors one at a time with the key on and watch whether the fault status clears
- Measure the resistance of every Bank 1 injector and compare the readings against each other and against specification
- With the driver module unplugged, check the high-side feed wire for continuity to ground and for battery voltage
- Inspect the harness under the valve cover and near hot components for melted or fuel-soaked insulation
- Repair the damaged harness or replace the shorted injector, then re-evaluate the driver module
- Clear the codes and confirm balanced injector operation and zero misfire counts on a road test