What does it mean?
P1594 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Charging System Voltage Too High .
Symptoms
- Check engine light on, often with the battery warning lamp and a charging system message
- Interior and exterior lighting noticeably brighter than usual and varying with engine speed
- Battery becoming hot, swelling or venting a sharp smell
- Bulbs and fuses failing repeatedly, and electronic accessories behaving strangely
- Voltmeter or trip computer showing an unusually high system voltage
- Cooling fans or blower running at odd speeds
Likely causes
- Voltage regulator inside the alternator failing in the high output direction
- Corroded or high resistance connection in the alternator control or sense circuit
- Poor engine and body ground straps, which make the regulator raise output to compensate
- Battery near the end of its life and no longer accepting charge properly
- Alternator or regulator from a different specification fitted during an earlier repair
- On systems where the module controls the alternator, a faulty control line or an incorrect duty cycle command
- Corroded battery terminals or a loose main output cable at the alternator
How to fix it
- Measure system voltage at the battery at idle and at raised rpm, with and without electrical loads switched on
- Carry out voltage drop tests on the alternator output cable and on the engine and body ground straps
- Check the alternator sense and control wiring for corrosion and high resistance
- Confirm the battery is serviceable with a load or conductance test
- On module-controlled charging systems, compare the commanded and measured generator voltage on the scan tool
- Correct any wiring or ground fault before replacing components
- Replace the regulator or alternator when the output remains high with good wiring, then recheck the whole system