P0599 on Chevrolet: How to Diagnose & Fix
Thermostat Heater Control Circuit High
1 Chevrolet model · 1 documented issue · $150-$600 repair
P0599 on Chevrolet by model: symptoms, diagnosis and fix
The 2011-2016 Cruze 1.4L turbo engine has chronic coolant leaks from the water outlet housing and thermostat housing. These plastic components crack from heat cycling. The turbo coolant feed and return lines also develop leaks at the crimped rubber-to-metal connections. Some owners report replacing the water outlet multiple times.
Common Symptoms
- Coolant puddle under vehicle
- Low coolant warning light
- Overheating in traffic
- Sweet coolant smell from engine bay
- Visible coolant residue on water outlet or thermostat housing
How to Fix
Check first: with the engine cold, look for wet coolant or dried coolant residue on the plastic water outlet, the thermostat housing, the water pump and the small turbo coolant lines. A cooling-system pressure test finds the leak, with tracer dye added if it is hard to spot. GM preliminary bulletin PI0740B (2011-2012 Cruze 1.4L) tells technicians to look for leaks or dye around the water pump seal and bolts, the thermostat housing, the heater core and the coolant surge tank. Don't mistake normal pump seepage for a leak. GM bulletin PI1041B says some seepage at the water pump's weep-reservoir plug is normal and can leave staining around it. If the pump is not leaving a trail of coolant down the front of the engine, nothing more should be done. Replace the pump only if its housing shows heavy coolant deposits. Repair: replace whichever part is leaking (the water outlet, the thermostat housing, or a hose or line), then refill the cooling system and get the air out of it. On CarComplaints, the fix 2013 owners report most often is replacing the plastic housing and its hose together. If the water pump is also leaking at its mounting bolts, GM bulletin PI0762C says not to tighten or seal the bolts but to replace the pump and gasket. The thermostat housing seal must be replaced along with the pump, and the pump gasket is ordered separately. Coverage: the GM programs cited here cover the water pump, not the water outlet or the thermostat housing. GM special coverage 14371B covered water pump leaks on 2011-2014 Cruze 1.4L cars for 10 years or 150,000 miles from the date the car was first put in service. For most of these cars, those 10 years have now passed. GM program 14417 ended August 12, 2016. It only topped up coolant on 2011-2014 Cruze 1.4L cars that lost coolant level because air was trapped at the factory, with no external leak. Don't keep driving a car that is overheating. One 2016 owner on CarComplaints had the pump, thermostat housing and water outlet replaced twice, once by the dealer and once themselves. The car kept overheating, and they found coolant mixed into the oil. Their dealer had quoted $872 for the repair.
Sources for this issue (8)
- Bob Is The Oil Guy - GM 1.4T coolant leak?forum
- CarComplaints - 2016 Cruze water pump / outlet / thermostat housingforum
- GM Special Coverage 14371B - Engine Coolant Leak from the Water Pump (2011-2014 Cruze, 2012-2014 Sonic 1.4L)tsb
- GM PI1041B - Information on Water Pump Replacement (LUJ/LUV)tsb
- GM PI0740B - Engine Coolant Odor inside Passenger Compartment (2011-2012 Cruze 1.4L)tsb
- GM PI0762C - Coolant Leak at Water Pump (2011-2012 Cruze 1.4L Turbo)tsb
- GM Customer Satisfaction Program 14417 - Low Engine Coolant Level without an External Leaktsb
- 2013 Chevrolet Cruze coolant leak - CarComplaints owner reportsowner-reports
P0599 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0599 mean on a Chevrolet?
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 Chevrolet it is documented across 1 model: Cruze.
What are the most common causes of P0599?
The most common causes of P0599 are: 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). The specific cause varies by vehicle.
How much does it cost to fix P0599 on a Chevrolet?
Published repair estimates on Chevrolet range from $150 to $600 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
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Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.