P0598
UniversalThermostat Heater Control Circuit Low
Medium SeverityThe engine's computer, known as the Powertrain Control Module (PCM), has detected a voltage reading that is too low in the circuit responsible for controlling the electric heater inside the engine coolant thermostat.
This typically means the engine may not warm up as quickly or efficiently as designed, potentially leading to increased fuel consumption and higher emissions.
⚠️ Before You Begin (Safety First)
Always allow the engine to cool completely before working on any cooling system components to avoid severe burns from hot coolant or engine parts. Disconnect the battery before performing any electrical diagnostics or repairs to prevent accidental short circuits or electrical shock. Use appropriate eye protection.
Common Symptoms
- Check Engine Light (MIL) illuminated
- Engine taking a longer time to reach operating temperature
- Reduced fuel economy
- Heater may not produce warm air as quickly or effectively
- Engine running cooler than optimal
Common Causes
- Faulty thermostat (specifically the integrated heater element)
- Open or short circuit in the thermostat heater control wiring
- Corroded or loose electrical connector at the thermostat
- Blown fuse for the thermostat heater circuit
- Faulty Engine Control Module (ECM) or Powertrain Control Module (PCM) (rare)
Frequently reported on: General/Universal
Diagnostic Steps
- Visually inspect the wiring harness and connectors leading to the thermostat for any signs of damage, fraying, or corrosion.
- Locate and check the fuse(s) associated with the thermostat heater circuit (refer to your vehicle's owner's manual or service information). Replace if blown.
- If accessible, disconnect the thermostat electrical connector and use a multimeter to check for continuity or resistance of the heater element within the thermostat (consult service manual for specific values).
- If the thermostat heater element tests faulty or if no other issues are found, replace the thermostat assembly.
- Clear the P0598 code with an OBD-II scanner and test drive the vehicle to ensure the repair is successful and the code does not return.
👨🔧 When to Call a Professional
While replacing the thermostat is often the fix, if you're not comfortable with electrical diagnostics using a multimeter, or if a new thermostat doesn't resolve the issue, consult a professional technician. Complex wiring issues or a faulty PCM require specialized tools and expertise.
Commonly Asked Questions
Can I continue driving my car with a P0598 code?
While you can typically drive with this code, it's advisable to address it soon. The engine may run less efficiently, consume more fuel, and produce higher emissions. Long-term, consistent cold running can also increase engine wear.
Does P0598 always mean I need a new thermostat?
Not necessarily. While a faulty thermostat (specifically its integrated heater) is a common cause, the issue could also be a blown fuse, damaged wiring, or a bad electrical connection to the thermostat. Always perform basic diagnostic checks first.
What tools do I need to diagnose and fix P0598?
You will likely need an OBD-II scanner to read and clear codes, a multimeter for electrical checks, and basic hand tools (sockets, wrenches) for accessing and replacing the thermostat.
Will replacing the thermostat fix my engine's poor gas mileage?
If the P0598 code is causing your engine to run cooler than its optimal operating temperature, fixing the issue by replacing the thermostat could certainly improve your fuel economy back to normal levels.
Where is the thermostat usually located on the engine?
The thermostat is typically housed in a thermostat housing on the engine block or cylinder head, often found near where the upper radiator hose connects to the engine.