OBD Guide
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P0599

Thermostat Heater Control Circuit High

P0599 is an OBD-II diagnostic trouble code meaning: Thermostat Heater Control Circuit High. Common causes: short circuit of the thermostat heater control wire to power (+12 v), broken feedback wire or thermostat ground. Estimated repair cost: $22–111.

Severity
⚠️ Medium
Can you drive?
Do not drive — repair immediately
Approx. repair cost
$22–111 (est.)

Symptoms

  • Check Engine light is on
  • The engine runs at a reduced operating temperature
  • Increased fuel consumption, especially in winter
  • Poor interior heating
  • Coolant temperature sensor shows low values

Causes

  • Short circuit of the thermostat heater control wire to power (+12 V)
  • Broken feedback wire or thermostat ground
  • Internal thermostat fault (always open)
  • Damage to wiring insulation
  • ECU malfunction (rare)

How to Fix

  1. Read error codes and check for additional temperature-related codes
  2. Inspect the thermostat connector and wiring for damage and melting.
  3. Check the voltage in the control circuit with the ignition on and the engine running.
  4. Check the insulation of the control wire for short circuit with power (+12 V)
  5. Measure the resistance of the thermostat heating element
  6. If the malfunction is confirmed, replace the thermostat assembly
  7. Reset error codes and perform a diagnostic test drive

Related codes

P0597P0598P0128P0116P0125

Error P0599 by Vehicle Brand

AcuraAudiBAICBMWBYDBuickCadillacChanganCheryChevroletChryslerCitroenDodgeDongfengExeedFAWFordForthingFotonGACGMGMCGeelyGreat WallHavalHondaHongqiHyundaiInfinitiJACJaecooJaguarJeepJetourKaiyiKiaLadaLexusLi AutoLifanLincolnLivanMazdaMercedes-BenzMercuryMitsubishiNIONissanOldsmobileOmodaOpelPeugeotPlymouthPontiacRenaultSWMSaturnSkodaSkywellSubaruSuzukiTankToyotaVolkswagenVolvoVoyahXPengZeekrZotye

FAQ

What does the P0599 code mean?

P0599 is an OBD-II diagnostic trouble code that indicates: Thermostat Heater Control Circuit High

What causes a P0599 error code?

The most common causes of P0599 include: Short circuit of the thermostat heater control wire to power (+12 V); Broken feedback wire or thermostat ground; Internal thermostat fault (always open); Damage to wiring insulation.

How do I fix a P0599 diagnostic trouble code?

To fix P0599: Read error codes and check for additional temperature-related codes. Inspect the thermostat connector and wiring for damage and melting.. Check the voltage in the control circuit with the ignition on and the engine running.. For a complete diagnosis, use an OBD-II scanner.

Is it safe to drive with P0599?

Do not drive — repair immediately

How much does it cost to fix P0599?

The estimated repair cost for P0599 is $22–111. Actual cost depends on your vehicle, location, and labor rates.

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