P1594

What it means

P1594 on a Jeep means the powertrain control module has seen the charging system voltage go higher than its expected limit. The module monitors battery or system voltage and sets the code when it stays too high, which points to over-charging from the alternator regulation or a fault in the control or sensing circuits. The exact regulation strategy and which part controls the alternator field vary by model and engine, so check the model-specific information.

Symptoms

• Battery warning light or charging system light on
• Check engine light on
• Headlights or interior lights unusually bright or flickering
• Battery that smells of sulphur, looks swollen or needs frequent topping up
• Erratic gauge readings or voltmeter reading high
• Other electronic modules behaving oddly or setting communication or voltage faults

Possible causes

• Faulty alternator voltage regulator (internal or external) allowing over-charginglikely
• Poor or corroded connections at the battery terminals, earth straps or alternator wiring giving the module a false or unstable voltage readinglikely
• Damaged wiring or connector in the alternator field control or sense circuit between the alternator and the powertrain control modulepossible
• Failing battery that cannot accept or hold charge properly, upsetting regulationpossible
• Fault in the powertrain control module's charging control driverrare
• Outdated control module software where the manufacturer has issued a known update for this coderare

How to diagnose

1. Read all stored codes and freeze frame data to see engine speed, load and system voltage when the code set, and note any other voltage or communication codes
2. Visually inspect the battery, terminals, earth straps, alternator plug and wiring for corrosion, looseness, heat damage or chafing
3. Measure battery voltage with the engine off, then at idle and at about 2,000 rpm with loads on and off; a reading persistently above the manufacturer's specified range confirms over-charging
4. Check the battery condition with a load or conductance test and look for signs of overheating or damage from over-charging
5. Check voltage drop on the charging positive and earth paths to rule out bad connections that cause a false reading
6. Test the alternator field or regulator control circuit for shorts, open circuits and correct signal using the model-specific wiring diagram
7. Check for applicable software updates or technical bulletins for the vehicle and engine
8. If all else passes, test the alternator output control and consider the control module as a last resort

How to fix

• Replace or repair the alternator or its regulator if it is over-charging
• Clean and tighten battery terminals and earth connections, and replace corroded or damaged leads
• Repair or replace damaged wiring or connectors in the alternator control or sense circuit
• Replace the battery if it is faulty or damaged by over-charging
• Update the control module software only if an applicable update exists for this fault, or repair or replace the module if proven faulty

Can I keep driving?

This code for other makes

• P1594BMWB Camshaft Position Actuator Control Open Circuit Bank 2
• P1594DodgeCharging System Voltage Too High
• P1594PlymouthCharging System Voltage Too High
• P1594PontiacCharging System Voltage Too High
• P1594SubaruAutomatic Transmission Diagnosis Input Signal Circuit Malfunction

Nearby codes

• P1499JeepOpen Or Shorted Condition Detected In The Hydraulic Cooling Fan Solenoid Control
• P1595JeepSpeed Control Solenoid Circuit Open Or Shorted