What does code P1594 mean?

Q: What does code P1594 mean?

Charging System Voltage Too High. P1594 on GM vehicles means the engine control module (ECM) has detected that the charging system voltage has risen above the safe limit, typically above 15.5 volts, for a sustained period. The ECM monitors the generator's output through the voltage sense circuit and commands the generator to reduce output when voltage climbs too high; this code sets when the commanded reduction fails to bring voltage back into range.

DTC codes / GM codes / P1594

P1594 · GMCharging System Voltage Too High

P1594 on GM vehicles means the engine control module (ECM) has detected that the charging system voltage has risen above the safe limit, typically above 15.5 volts, for a sustained period. The ECM monitors the generator's output through the voltage sense circuit and commands the generator to reduce output when voltage climbs too high; this code sets when the commanded reduction fails to bring voltage back into range.

SystemPowertrain

Code typeGM specific

SeverityHigh

Fix difficultyIntermediate

AreaVehicle speed, idle control and auxiliary inputs

Guidance is general and written for GM vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.