OBD-II code · Powertrain (generic)
P0599 Thermostat Heater Control Circuit High
Same as P0597 with the control line shorted to supply. The sensor heater warms the element to operating temperature (~600 °C); without it the lambda sensor stays inactive in closed loop and the ECM cannot trim mixture.
Is it safe to drive with P0599?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyControl line shorted to supply
- Less likelyConnector pins corroded - high contact resistance
- Less likelySupply wire pinched against B+ source
Repair at a glance
- Difficulty
- Medium
- DIY friendly
- Often, with basic tools
- Typical labour
- 0.5–2 h
- Emissions test
- Likely to fail
- Parts involved
- Map Thermostat Heater
Related codes
- P0596Cruise Control Servo Control Circuit High
- P0597Thermostat Heater Control Circuit Open
- P0598Thermostat Heater Control Circuit Low
- P059AActive Grille Air Shutter A Position Sensor Circuit
- P059BActive Grille Air Shutter A Position Sensor Range or Performance
- P059CActive Grille Air Shutter A Position Sensor Circuit High
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.