P0594 - DTC P0594 - Thermostat Control Circuit Range/Performance Problem in Popular Vehicles

Quick Answer

P0594 means: P0594 indicates a thermostat control circuit issue, affecting engine temperature regulation.

Fix: Check and replace faulty components Cost: $150 - $300 Time: 90-180 minutes

Can I drive with P0594? Immediate attention is recommended to prevent engine damage.

Common Questions

What does P0594 mean and how does it affect my car?

The P0594 code indicates an issue with the thermostat control circuit, which can lead to improper engine temperature regulation. This can cause engine overheating, poor fuel efficiency, and increased emissions, ultimately affecting the vehicle's performance and lifespan.

What are the most common causes of P0594 and how much does it cost to fix?

The most common cause of P0594 is a faulty thermostat, which can cost between $150 and $300 to replace. Other causes include wiring issues and faulty sensors, with repair costs ranging from $50 to $200.

Can I drive my car with P0594 or should I stop immediately?

It's recommended to stop driving the vehicle if you see the P0594 code, as ignoring it can lead to severe engine damage due to overheating.

How can I diagnose P0594 myself using GeekOBD APP?

With the GeekOBD APP, you can scan for diagnostic codes, view live data from the thermostat and ECT sensor, and check for freeze frame data to understand the conditions when the code was set.

What vehicles are most commonly affected by P0594?

The P0594 code is frequently seen in vehicles such as the 2013-2018 Chevrolet Malibu, 2015-2019 Ford F-150, and many models from brands like Dodge and Chrysler during similar years.

How can I prevent P0594 from happening again?

Regular maintenance of your vehicle’s cooling system, including coolant flushes and inspections of the thermostat and wiring, can help prevent future occurrences of DTC P0594.

What is P0594?

The diagnostic trouble code (DTC) P0594 indicates a thermostat control circuit range or performance issue. This code is primarily related to the engine's cooling system, specifically the thermostat's ability to regulate engine temperature effectively. When the vehicle’s engine control module (ECM) detects that the thermostat is not functioning within the expected parameters, it triggers this code. Commonly seen in vehicles like the 2013-2018 Chevrolet Malibu and 2015-2019 Ford F-150, a P0594 can lead to engine overheating, poor fuel economy, and increased emissions. The thermostat plays a critical role in maintaining optimal engine temperature by controlling the flow of coolant. If it fails open, the engine may run too cold, which can lead to inefficient combustion and increased emissions. Conversely, if it fails closed, the engine may overheat, causing serious damage. Real-world implications include potential engine damage if not addressed promptly, making it essential for drivers to understand this code's significance, its symptoms, and necessary repairs.

System: P - Powertrain (Engine, Transmission, Emissions)

Symptoms

Common symptoms when P0594 is present:

Check engine light illuminates and remains on consistently, indicating a potential issue that needs immediate attention.
Engine struggles to maintain optimal temperature, leading to noticeable fluctuations on the temperature gauge.
Fuel economy may drop significantly, often by 10-15%, due to improper engine temperature affecting combustion efficiency.
Overheating of the engine can occur, leading to potential long-term damage if ignored.
Increased emissions may be observed, as the vehicle may not be operating within the optimal temperature range.

Possible Causes

Most common causes of P0594 (ordered by frequency):

{'cause': 'Faulty thermostat, likely the most common cause (70%) - The thermostat may be stuck open or closed, hindering proper coolant flow.', 'details': 'This can lead to inefficient engine performance and overheating.'}
{'cause': 'Wiring issues or damaged connectors (20%) - Corroded or broken wires in the thermostat control circuit can disrupt communication with the ECM.', 'details': 'Inspect wiring and connectors for any visible damage.'}
{'cause': 'Faulty Engine Coolant Temperature (ECT) sensor (5%) - An incorrect reading from the ECT sensor can mislead the ECM, causing the thermostat to function improperly.', 'prevention': 'Regularly check and replace faulty sensors during routine maintenance.'}
{'cause': "Cooling system blockage (3%) - Debris or sludge in the cooling system can affect the thermostat's operation.", 'details': 'Flush the cooling system periodically to prevent blockages.'}
{'cause': 'Rarely, a malfunctioning ECM (2%) - The ECM itself may develop issues leading to incorrect thermostat control.', 'details': 'This is less common but can be diagnosed with advanced scanning tools.'}

P0594 Repair Costs

Cost Breakdown by Repair Type

Thermostat Replacement

Replacing the thermostat is often the primary fix for a P0594 code.

Total: $150 - $300
Success rate: 95%

Wiring Repair

Repairing damaged wiring or connectors in the thermostat control circuit.

Total: $50 - $150
Success rate: 85%

ECT Sensor Replacement

Replacing a faulty Engine Coolant Temperature sensor to ensure accurate readings.

Total: $100 - $200
Success rate: 90%

Money-Saving Tips for P0594

Start with the most common and least expensive repairs first
Use GeekOBD APP to confirm diagnosis before replacing expensive parts
Consider preventive maintenance to avoid future occurrences
Compare prices for OEM vs aftermarket parts based on your needs
Address the issue promptly to prevent more expensive secondary damage

Diagnostic Steps

Professional P0594 Diagnosis Process

Follow these systematic steps to accurately diagnose P0594. Each step builds on the previous one to ensure accurate diagnosis.

Step 1: Step 1

Step 1: Initial visual inspection - Check for obvious signs like damaged wiring, loose connections, or corrosion (5-10 minutes)