Thermostat Heater Control Circuit Low
The P0598 code indicates that the powertrain control module (PCM) has detected a low voltage condition in the thermostat heater control circuit. This circuit is responsible for heating the engine thermostat to regulate coolant temperature more precisely, improving fuel economy and emissions. A low voltage reading suggests a short to ground, open circuit, or faulty component in the heater circuit, which can prevent the thermostat from opening properly and cause the engine to run cooler than optimal.
01. Most Common Causes
- Shorted or open thermostat heater circuit wiring
- Faulty thermostat heater element
- Corroded or damaged connector at thermostat
- Failed PCM (rare)
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Engine running cooler than normal (low coolant temperature gauge reading)
- Poor fuel economy
- Possible heater performance issues (slow cabin heat)
03. Step-by-Step Diagnosis
Step 1: Use a scan tool to confirm code P0598 and check for related codes.
Step 2: Visually inspect the thermostat heater connector and wiring for damage, corrosion, or loose connections.
Step 3: Measure resistance of the thermostat heater element; compare to manufacturer specs (typically 10-30 ohms).
Step 4: Check for voltage at the heater connector with key on; should be battery voltage. If not, test circuit continuity and check for shorts to ground.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is generally safe to drive short distances, but the engine may not reach optimal operating temperature, leading to reduced fuel economy and increased emissions. Prolonged driving could cause other issues, so it's best to diagnose and repair promptly.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150 for parts and labor, depending on whether the thermostat assembly needs replacement or just wiring repairs. Thermostat replacement parts cost around $30-$80, and labor adds $50-$100.