P0598: Thermostat Heater Control Circuit Low
What to do
Driveable. If the engine takes a long time to warm up or the heater is weak in cold weather, that is the likely consequence. Worth fixing before winter.
What this code means
The thermostat heater circuit is reading low — a short to ground, or a driver holding the circuit down. A heater energised continuously holds the thermostat open, so the engine runs cooler than intended and may take a long time to reach temperature in cold weather.
That is worth noticing, because a persistently cool engine wears faster, uses more fuel, and gives a weak cabin heater — and it is easy to blame the thermostat itself when the fault is in the circuit driving its heater.
Likely causes
Start here
- Signal wire shorted to ground · moderate
- Failed thermostat heater element · moderate
- Corroded or loose connector · easy
Rare
- Control module driver failure · specialist
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
Be the first to write this up
Nothing posted about this yet. Whatever you found is worth writing down — even a dead end saves someone the same afternoon.
What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
Sign in or create an account to add what you found about P0598.