P0598Thermostat Heater Control Circuit Low
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- A map-controlled thermostat is a wax thermostat with a built-in heating resistor (Valeo: about 10 Ω). Unheated it opens late, for hot running at part load; the engine module heats it by map under full load or towing so it opens earlier. CARB requires the thermostat to be monitored and the heater circuit counts as an output component. GM switches it to ground with a low-side driver and checks it every second, fault after 15 of 30 samples, type B; Hyundai/Kia/Genesis and VW/Audi use the codes as well. P0598 means the control line is shorted to ground – GM detects 0.5 Ω with the driver off. With a low-side driver the heater then stays on permanently and the thermostat opens early, so the engine runs cool; Kia's Cadenza bulletins list it with P0128 and replace the thermostat.
- What you may notice
- Check engine light on
- Engine slow to reach operating temperature (possibly P0128)
- Weak cabin heating in winter, higher consumption
- Likely causes
- LikelyInternal short in thermostat or heater, coolant in the connector
- PossibleControl line shorted to ground (chafing)
- RareEngine module driver
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €120 – €600
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.