P0599 on Mercedes-Benz
Thermostat Heater Control Circuit High
P0599 on Mercedes-Benz vehicles indicates thermostat heater control circuit high. Au7o has documented this code across 1 Mercedes-Benz model — most commonly on GLA. This code relates to the engine cooling system's thermostat heater control circuit, used on engines with an electrically heated (map-controlled) thermostat that the computer can open early to fine-tune coolant temperature. The 'high' designation means the computer detected the control circuit voltage was higher than expected, indicating an electrical fault such as a short to voltage or an open circuit. It is generally an electrical/wiring problem rather than a mechanical cooling failure. It can affect how precisely the engine manages its operating temperature and fuel economy. Typical repair costs on Mercedes-Benz range from $400 to $1,200, depending on the specific model and root cause.
Common Causes of P0599
- •Faulty electronically heated thermostat element/heater
- •Short to voltage in the heater control circuit
- •Open or damaged wiring/connector
- •Corroded or loose connector at the thermostat
- •Poor electrical ground
- •Faulty PCM/ECM driver (less common)
P0599 on Mercedes-Benz by Model
Mercedes-Benz GLA(1 issue)
- Water Pump Failure2015-2020
The electric water pump on the M270 engine fails, causing loss of coolant circulation and rapid overheating. The pump motor or impeller breaks, and failure is often sudden with no warning. Common between 50,000-90,000 miles.
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View P0599 across all makes →Frequently Asked Questions
What does P0599 mean on Mercedes-Benz?▼
P0599 stands for "Thermostat Heater Control Circuit High." This code relates to the engine cooling system's thermostat heater control circuit, used on engines with an electrically heated (map-controlled) thermostat that the computer can open early to fine-tune coolant temperature. The 'high' designation means the computer detected the control circuit voltage was higher than expected, indicating an electrical fault such as a short to voltage or an open circuit. It is generally an electrical/wiring problem rather than a mechanical cooling failure. It can affect how precisely the engine manages its operating temperature and fuel economy. On Mercedes-Benz specifically, this code is documented across 1 model.
What causes P0599 on Mercedes-Benz vehicles?▼
Common causes on Mercedes-Benz: Faulty electronically heated thermostat element/heater, Short to voltage in the heater control circuit, Open or damaged wiring/connector, Corroded or loose connector at the thermostat, Poor electrical ground. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0599 on a Mercedes-Benz?▼
Repair costs on Mercedes-Benz range from $400 to $1,200, depending on the specific model and root cause.
Which Mercedes-Benz models have P0599 documented?▼
Au7o has documented P0599 on 1 Mercedes-Benz model: GLA.