What P0598 means
A map-controlled thermostat is a wax thermostat with a built-in heating resistor (Valeo: about 10 Ω).
How the engine computer detects it
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.
Written from public technical sources and not yet checked by a mechanic. How we write these pages
Symptoms
- Check engine light on
- Engine slow to reach operating temperature (possibly P0128)
- Weak cabin heating in winter, higher consumption
Common causes
- Internal short in thermostat or heater, coolant in the connector Most likely
- Control line shorted to ground (chafing) Possible
- Engine module driver Less likely
How to diagnose P0598
- Read every stored code with an OBD-II scanner. If misfire or fuel trim codes are there too, fix those first: they often cause this one.
- Inspect the parts involved: map controlled thermostat, thermostat heater, heater wiring, engine control module.
- Work through the causes above from most to least likely, cheapest checks first.
- Clear the code and drive a full drive cycle to confirm the repair held.
Vehicles that report P0598 most
| Vehicle | Years | Reports | Share | Median miles |
|---|---|---|---|---|
| Chevrolet Volt | 2016–2018 | 4 | — |
Counts of owner complaints to the NHTSA that mention P0598 (5 in total), not failure rates: popular models get more complaints simply because more of them are on the road. Models with fewer than 3 complaints are left out.
Reading the code
- P
- Powertrain
- 0
- Generic (SAE) code
- 5
- Vehicle speed, idle control and auxiliary inputs
- 98
- Specific fault
Questions drivers ask
Can I drive with code P0598?
Usually yes for a short time, if the car drives normally, the temperature gauge reads normal and the check engine light is steady. If the light flashes, the engine loses power or overheats, or other warning lights come on, pull over and have it checked.
Will my car pass an emissions inspection with P0598?
Probably not in states that test vehicles with an OBD-II scan: an emissions-related code that keeps the check engine light on is usually an automatic fail. Rules differ by state and county, so check yours.
Will P0598 clear by itself?
The light can go off after several drive cycles without the fault, but the code returns if the cause is still there. After a repair, the readiness monitors need a full drive cycle before an inspection.
Can I fix P0598 myself?
Often yes, with an OBD-II scanner and basic tools. Difficulty: medium. Start with the cheapest checks before replacing expensive parts.
Often reported together
Codes that owners mention in the same NHTSA complaints as P0598. They can point to a shared cause, so it's worth checking them together.
- P0597Thermostat Heater Control Circuit/Open5 complaints
- P0030HO2S Heater Control Circuit (Bank 1 Sensor 1)4 complaints
- P0031HO2S Heater Control Circuit Low (Bank 1 Sensor 1)4 complaints
- P0135O2 Sensor Heater Circuit Bank 1 Sensor 14 complaints
- P0443EVAP System Purge Control Valve A Circuit4 complaints
- P0458EVAP System Purge Control Valve A Circuit Low4 complaints
This page is general information, not a substitute for a professional diagnosis. Repair costs are rough estimates for parts and labor and vary by vehicle and region.