Thermostat Heater Control Circuit High
The P0599 code indicates that the powertrain control module (PCM) has detected a high voltage condition in the thermostat heater control circuit. This circuit is responsible for regulating the engine coolant temperature by controlling the thermostat's heating element. A high voltage reading suggests a short to power, a faulty thermostat heater, or a wiring issue. This can cause the thermostat to remain open or closed, leading to improper engine temperature regulation.
1. Most Common Causes
- Shorted thermostat heater circuit
- Faulty thermostat heater element
- Damaged wiring or connector
- PCM failure (rare)
2. Symptoms You Will Notice
- Check Engine Light illuminated
- Engine overheating or running too cool
- Poor fuel economy
- Erratic temperature gauge readings
3. Step-by-Step Diagnosis
Step 1: Scan for codes and verify P0599 is present.
Step 2: Visually inspect the thermostat heater connector and wiring for damage or corrosion.
Step 3: Test the thermostat heater resistance with a multimeter; compare to manufacturer specs.
Step 4: Check for voltage at the heater connector with key on; if voltage is high, repair short to power.
Step 5: If all checks pass, replace the thermostat assembly.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances as the engine may overheat or run too cool, potentially causing damage. Have it diagnosed promptly.
How much does it cost to fix?▼
The repair typically costs between $50 and $150 for parts and labor, depending on the vehicle and whether the thermostat assembly needs replacement.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.