P0599 on Cadillac
Thermostat Heater Control Circuit High
P0599 on Cadillac vehicles indicates thermostat heater control circuit high. Au7o has documented this code across 1 Cadillac model — most commonly on STS. This code relates to the engine cooling system's thermostat heater control circuit, used on engines with an electrically heated (map-controlled) thermostat that the computer can open early to fine-tune coolant temperature. The 'high' designation means the computer detected the control circuit voltage was higher than expected, indicating an electrical fault such as a short to voltage or an open circuit. It is generally an electrical/wiring problem rather than a mechanical cooling failure. It can affect how precisely the engine manages its operating temperature and fuel economy. Typical repair costs on Cadillac range from $3,000 to $6,000, depending on the specific model and root cause.
Common Causes of P0599
- •Faulty electronically heated thermostat element/heater
- •Short to voltage in the heater control circuit
- •Open or damaged wiring/connector
- •Corroded or loose connector at the thermostat
- •Poor electrical ground
- •Faulty PCM/ECM driver (less common)
P0599 on Cadillac by Model
Cadillac STS(1 issue)
- 4.6L Northstar V8 Head Gasket Failure and Bolt Pull-Out1998-2011
The Northstar V8 in the STS is infamous for head gasket failure caused by the head bolts pulling out of the aluminum block. GM used torque-to-yield head bolts threaded directly into the aluminum block without steel inserts, and over time the bolt threads strip from the soft aluminum. Coolant enters the combustion chambers, causing overheating and white exhaust smoke. This issue affects virtually every high-mileage Northstar engine and is often terminal for the vehicle due to repair costs exceeding vehicle value.
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What does P0599 mean on Cadillac?▼
P0599 stands for "Thermostat Heater Control Circuit High." This code relates to the engine cooling system's thermostat heater control circuit, used on engines with an electrically heated (map-controlled) thermostat that the computer can open early to fine-tune coolant temperature. The 'high' designation means the computer detected the control circuit voltage was higher than expected, indicating an electrical fault such as a short to voltage or an open circuit. It is generally an electrical/wiring problem rather than a mechanical cooling failure. It can affect how precisely the engine manages its operating temperature and fuel economy. On Cadillac specifically, this code is documented across 1 model.
What causes P0599 on Cadillac vehicles?▼
Common causes on Cadillac: Faulty electronically heated thermostat element/heater, Short to voltage in the heater control circuit, Open or damaged wiring/connector, Corroded or loose connector at the thermostat, Poor electrical ground. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0599 on a Cadillac?▼
Repair costs on Cadillac range from $3,000 to $6,000, depending on the specific model and root cause.
Which Cadillac models have P0599 documented?▼
Au7o has documented P0599 on 1 Cadillac model: STS.