System: Powertrain (P-Code)
SAE Standard (Generic)
Family: Thermostat Heater Control Circuit
Code P0599: Thermostat Heater Control Circuit High
Diagnostic & Technical Explanation
Code P0599 (Thermostat Heater Control Circuit High) sets when the ECM detects an open circuit, out-of-range current, or a performance fault while driving the electric heating element built into a map-controlled thermostat used to fine-tune coolant temperature for emissions and fuel economy. Causes are a failed heater element inside the thermostat, a corroded connector, or damaged control wiring.
First-listed procedure
Rank #1
Inspect thermostat heater connector
Easy DIY
This is the first procedure in the authored
consideration order, not a measured cause likelihood. Execute it only when its prerequisites
and diagnostic findings support it. Its cost and labor estimates (where known), the step-by-step procedure and the
remaining 2 procedure(s) are in the licensed dataset. Ordering context.
Full family: Thermostat Heater Control Circuit
What this page does not show
This page publishes the fault mechanism and the code index. The licensed dataset adds, for
every one of the 15,886 codes, the full authored repair set (56,729 procedures in total)
with the fields deliberately withheld here:
- Procedures 2..n after the first-listed procedure
- Aftermarket parts cost ranges in USD (
est_parts_cost_min/max_usd)
- Professional labor-hour estimates (
est_labor_hours)
- Step-by-step diagnostic and repair instructions
- Replacement-part mappings and catalog lookups
- 6,637 manufacturer-specific OEM codes across 32 makes ($149 tier)