Code Definition

P0599 — Thermostat Heater Control Circuit High

System: Powertrain  |  Type: Generic (OBD-II Standard)  |  Make: Generic

About P0599

P0599 is a generic (obd-ii standard) powertrain diagnostic trouble code. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

When P0599 is stored, the module has detected a signal or supply voltage higher than the expected operating range.

Scanning & clearing: A generic OBD-II scan tool will usually read and clear powertrain (P) codes. For live data, freeze-frame capture, and bi-directional tests you may need a more capable scan tool that supports the vehicle's ECM protocol.

Because P0599 is a generic OBD-II code, its base definition is shared across manufacturers. The specific diagnostic steps, reference values, and repair procedures can vary by vehicle, and the TaT Diagnostic Assistant includes verified procedures submitted by working technicians.

Code Information

This fault code is logged when the engine control module (ECM) detects a higher than normal voltage in the thermostat heater control circuit. In modern vehicles, the thermostat often includes an integrated electric heater, which is controlled by the ECM to more precisely manage the engine's temperature. The thermostat heater assists in regulating the opening of the thermostat, facilitating efficient engine warm up and optimal coolant temperature control. A high voltage condition in this circuit could indicate an electrical fault such as an open circuit or a poor ground connection, potentially ...

Join TaT to view the complete code information and diagnostic details.

Quick Facts