What does it mean?
P1284 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Fuel Injection Pump Battery Voltage Out-Of-Range .
Symptoms
- The MIL is on, often with other modules storing voltage related codes
- Hard starting, extended cranking or an intermittent no start
- Engine stalling at idle or cutting out while driving, then restarting
- Rough running, misfire and loss of power under load
- Dim or flickering lights and a battery warning lamp if charging is the cause
- Fault worse in cold weather or with heavy electrical loads switched on
Likely causes
- Weak, discharged or internally failing battery with high resistance
- Corroded or loose battery terminals, main earth strap or engine ground
- Charging system fault such as a worn alternator, failed regulator or a slipping belt
- High resistance in the supply feed to the injection pump module, including its fuse and relay
- Corroded connector at the pump driver or a damaged section of the supply harness
- Excessive voltage drop during cranking because of a tired starter drawing heavy current
- Faulty pump control electronics that misread an otherwise good supply
How to fix it
- Load test the battery and check its state of charge before looking at anything else
- Measure charging voltage at idle and at raised rpm, with and without electrical loads
- Clean and tighten the battery terminals, the main earth strap and the engine to body ground
- Back-probe the injection pump supply and watch the voltage during cranking and while driving, comparing with battery voltage
- Voltage drop test the supply through the fuse holder, relay and each connector on the way to the pump electronics
- Inspect the pump connector for corrosion, heat damage and loose terminals
- Repair the high resistance connection, replace the battery or charging component as proven, then verify a stable supply on live data