P1594

What it means

On Dodge vehicles P1594 means the powertrain control module has seen the charging system voltage rise above its expected limit. This is usually judged from battery voltage sensed at the PCM while the engine is running, compared with the target voltage the PCM is commanding from the alternator or generator field. The exact thresholds and how the alternator is controlled depend on the model and year.

Symptoms

• Battery or charging warning light on, or check engine light on
• Headlights and interior lights unusually bright or flickering
• Battery that is hot, swollen, or smells of rotten eggs
• Voltmeter reading high on the dashboard, where fitted
• Blown fuses or failed bulbs and electronic modules
• Intermittent running or stalling in some cases

Possible causes

• Faulty alternator or internal voltage regulator overcharginglikely
• Poor connection or fault in the alternator field control circuit between the PCM and the alternator (open, short or corroded terminals)likely
• Loose, corroded or damaged battery terminals, or poor earth and sense wiring causing incorrect voltage readingspossible
• Failing or internally shorted battery giving false voltage readings or abnormal charging behaviourpossible
• Fault in the PCM voltage sensing or field driver circuitrare
• Outdated PCM software where a known charging control issue exists for that model (check manufacturer bulletins)rare

How to diagnose

1. Read all stored and pending codes and the freeze frame data, noting engine speed, load and battery voltage when the fault set
2. Visually inspect the battery terminals, earth straps, alternator connector and wiring for corrosion, heat damage or looseness
3. Check the battery condition and state of charge, and test it for internal faults before blaming the alternator
4. With a multimeter, measure battery voltage at rest, then at idle and at about 2,000 rpm with loads on and off, and compare with the specification for that model
5. Compare the voltage at the battery with the voltage at the alternator output to find voltage drop or sensing faults
6. Check the field control circuit between the PCM and the alternator for continuity, shorts to voltage or earth, following the wiring diagram for that vehicle
7. Check for relevant technical service bulletins or software updates for the specific model and engine
8. Clear the code and road test to confirm it does not return and that charging voltage stays within specification

How to fix

• Replace the alternator if it overcharges or its regulator is faulty
• Repair or replace damaged wiring, connectors or terminals in the field control circuit
• Clean and tighten battery terminals and repair poor earth connections
• Replace the battery if it is faulty and has damaged or confused the charging system
• Apply a manufacturer-approved PCM software update if an outdated calibration is a known cause for that model
• Replace the PCM only after wiring, alternator and battery have all been proven good

Can I keep driving?

This code for other makes

• P1594BMWB Camshaft Position Actuator Control Open Circuit Bank 2
• P1594JeepCharging System Voltage Too High
• P1594PlymouthCharging System Voltage Too High
• P1594PontiacCharging System Voltage Too High
• P1594SubaruAutomatic Transmission Diagnosis Input Signal Circuit Malfunction

Nearby codes

• P1499DodgeOpen Or Shorted Condition Detected In The Hydraulic Cooling Fan Solenoid Control
• P1595DodgeSpeed Control Solenoid Circuit Open Or Shorted