Error code

OBD2 P0599

OBD2P0599
Diagnostic Trouble Code· Standard OBD-II fault code read from the vehicle's onboard diagnostics.

What it means

Thermostat Heater Control Circuit High.

Severity

moderateCan drive, but performance issues and potential overheating may occur.

Summary

P0599 indicates an issue with the thermostat heater control circuit in your vehicle's cooling system, specifically that there is excessive voltage detected by the PCM (Powertrain Control Module). This code typically affects vehicles equipped with electronically heated thermostats.

Symptoms

  • Rich exhaust
  • Cold start drivability issues
  • No heat inside the passenger compartment
  • Diminished engine performance

Common Causes

  • Thermostat heater element burned out (very common)
  • Defective primary or secondary ECT sensor
  • Faulty ambient temperature sensor
  • Shorted or open circuits or connectors
  • Bad thermostat
  • Low engine coolant

Diagnosis

  1. Retrieve all stored codes and freeze frame data using a diagnostic scanner.
  2. Perform a visual inspection of related wiring and connectors for damage or wear.
  3. Use a digital volt/ohmmeter (DVOM) to test voltage and ground circuits at the thermostat heater or PCM.
  4. Check system relays and related fuses, replacing any that are defective.

Fixes

  • Replace the faulty thermostat heater element if burned out.

FAQ

What does P0599 mean?

P0599 indicates excessive voltage in the thermostat heater control circuit, which is part of your vehicle's cooling system.

How do I fix P0599?

Fixing P0599 typically involves replacing a faulty thermostat heater element or addressing issues with wiring and connectors.

View source

Not affiliated with OBD2. Answer summarized from the manufacturer's manual linked above; consult that source for the authoritative procedure.

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