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P0597 – What Does It Mean and How To Fix It

This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.


P0597 is an OBD-II Code that refers to Thermostat Heater Control Circuit Open


A P0597 code is a general diagnostic trouble code that occurs when the ECM/PCM detects that a failure in the electronically controlled engine thermostat system. It indicates that the control voltage is non-existent. The thermostat has several load temperature sensors. 

The thermostat heater’s main job is to regulate the flow of coolant as well as the engine’s operating temperature. The Engine Control Module (ECM) provides 12 volts for the thermostat.

The DTC code P0597 OBD II is set if the ECM detects an incorrect signal from the thermostat.


Common causes for this code include:

  • Coolant leakage
  • Bad thermostat
  • Open or shorted wiring harness in thermostat
  • Malfunctioning Motronic computer (rare)


The symptoms of a P0597 code are:

  • Illuminated Check Engine Light
  • If the thermostat fails in the closed position, high temperature readings are possible
  • If the thermostat fails in the open position, a low temperature reading is recorded


To diagnose a P0597 DTC code, a technician would:

  1. Scan for codes in the ECM and look at the freeze frame data for failure.
  2. Visually inspect all related wiring and connectors.
  3. Check for proper operation of the thermostat.
  4. Check for any engine overheating conditions.

Common mistakes

The following are some of the most common mistakes that a technician may make when diagnosing a P0597 code:

  • Not thoroughly inspecting all the wiring and connectors for damage.
  • Not checking for engine overheating conditions.
  • Failing to properly test the thermostat.

How serious is this?

A P0597 code is a serious code that can lead to engine damage if left unresolved as high temperatures can cause serious engine damage.

What repairs can fix the code?

The following are solutions that may fix this problem:

  • Repair or replace any damaged wiring and connectors.
  • Replace the thermostat.
  • Check for engine overheating conditions.
  • Properly test the thermostat.
  • Clear all codes and retest the system to see if the code comes back.

Related codes

A P0597 is related to and may be accompanied by the following codes:

P0128 – Thermostat (Coolant) Malfunction

P0607 – Control Module Performance

P0600 – Serial Communication Link Malfunction

B1342 – Battery Disconnect Switch Circuit Open

U0401 – Implausible Data Received From ECM/PCM


In conclusion, the P0597 code is a diagnostic trouble code that refers to a problem with the thermostat heater control circuit. This code is a serious code that can lead to engine damage if left unresolved as high temperatures can cause serious engine damage. Some of the common causes for this code include coolant leakage, a bad thermostat, or open or shorted wiring in the thermostat. The most common symptom of this code is an illuminated Check Engine Light.