P0591 - Thermostat Control Circuit Range/Performance Problem in Popular Vehicles

Quick Answer

P0591 means: P0591 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 P0591? Immediate diagnosis is recommended to prevent engine damage.

Common Questions

What does P0591 mean and how does it affect my car?

The P0591 code indicates a thermostat control circuit issue, which can disrupt engine temperature regulation. This may lead to overheating, poor fuel efficiency, and even engine damage if left unaddressed.

What are the most common causes of P0591 and how much does it cost to fix?

Common causes include a faulty thermostat, damaged wiring, or issues with the ECM. Repair costs can range from $150 for a thermostat replacement to $600 for ECM reprogramming.

Can I drive my car with P0591 or should I stop immediately?

It's advisable to stop driving your vehicle if the P0591 code appears, as it may lead to overheating and severe engine damage if not resolved quickly.

How can I diagnose P0591 myself using GeekOBD APP?

Using the GeekOBD APP, scan your vehicle to retrieve diagnostic trouble codes. Investigate the freeze frame data for context about the engine's condition when the code triggered, and check the thermostat's function.

What vehicles are most commonly affected by P0591?

Commonly affected vehicles include the 2015-2018 Honda Accord, 2016-2020 Toyota Camry, and 2013-2016 Ford Fusion, among others. It's important to check for any recalls or technical service bulletins related to this issue.

How can I prevent P0591 from happening again?

Regular maintenance, including coolant checks and thermostat inspections, can help prevent P0591. Ensure you use quality parts if you replace components and address any symptoms promptly.

What is P0591?

The P0591 diagnostic trouble code (DTC) indicates a problem with the engine's thermostat control circuit. This code is commonly triggered when the Engine Control Module (ECM) detects that the thermostat is not functioning within the expected range of parameters. Essentially, the thermostat is responsible for regulating the engine's temperature by controlling the flow of coolant. When it fails to do so, it can lead to overheating or insufficient heating of the engine, impacting performance and fuel efficiency. Commonly affected vehicles include the 2015-2018 Honda Accord, 2016-2020 Toyota Camry, and 2013-2016 Ford Fusion, where drivers may notice irregular engine temperatures and a decrease in fuel economy. Ignoring this code can lead to serious engine damage over time, which may result in costly repairs. Therefore, addressing a P0591 code promptly is crucial for maintaining vehicle health and performance.

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

Symptoms

Common symptoms when P0591 is present:

  • Check engine light stays on constantly, indicating a persistent issue that needs attention.
  • Engine temperature fluctuates unexpectedly, which can lead to overheating or poor cabin heating during winter months.
  • Fuel economy decreased by 10-15%, making trips less efficient and costing more at the pump.
  • Engine performance issues, such as rough idling or stalling, may occur due to improper temperature regulation.
  • In some cases, coolant leaks might appear, signaling a failing thermostat that needs replacement.

Possible Causes

Most common causes of P0591 (ordered by frequency):

  1. The most common cause of the P0591 code is a faulty thermostat, which is likely to occur in about 60% of reported cases. A thermostat that is stuck open or closed can severely disrupt engine temperature management.
  2. Another potential cause is a damaged wiring harness or connector related to the thermostat, which can lead to improper readings. This issue accounts for roughly 20% of occurrences.
  3. A malfunctioning Engine Control Module (ECM) can also trigger this code, albeit less frequently (about 10%). If the ECM is not processing signals correctly, it may misinterpret the thermostat's function.
  4. Less commonly, low coolant levels or a coolant leak could cause the system to register incorrect temperatures, leading to the P0591 code.
  5. In rare cases, aftermarket parts or incorrect thermostat replacements can lead to repeated P0591 codes due to compatibility issues.

P0591 Repair Costs

Cost Breakdown by Repair Type

Thermostat Replacement

Replacing the thermostat is the most common and effective repair for the P0591 code.

  • Total: $150 - $300
  • Success rate: 85%
Wiring Repair

Repairing damaged wiring can prevent future issues related to the thermostat circuit.

  • Total: $75 - $150
  • Success rate: 90%
ECM Reprogramming

In rare cases, reprogramming or replacing the ECM may be necessary if it fails to process signals correctly.

  • Total: $200 - $600
  • Success rate: 70%
Money-Saving Tips for P0591
  • 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 P0591 Diagnosis Process

Follow these systematic steps to accurately diagnose P0591. Each step builds on the previous one to ensure accurate diagnosis.

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

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

GeekOBD APP Tip: Use GeekOBD APP to monitor real-time data during this diagnostic step for accurate results and professional-grade analysis.
Step 2: Step 2: OBD2 scan with GeekOBD APP - Retrieve all codes and freeze frame data to understand the fault context, which will help establish if P0591 is the only code present (10-15 minutes)

Step 2: OBD2 scan with GeekOBD APP - Retrieve all codes and freeze frame data to understand the fault context, which will help establish if P0591 is the only code present (10-15 minutes).

GeekOBD APP Tip: Use GeekOBD APP to monitor real-time data during this diagnostic step for accurate results and professional-grade analysis.
Step 3: Step 3: Component testing - Use a multimeter or specific diagnostic tools to test the thermostat's resistance and the wiring harness for continuity (20-30 minutes)

Step 3: Component testing - Use a multimeter or specific diagnostic tools to test the thermostat's resistance and the wiring harness for continuity (20-30 minutes).

GeekOBD APP Tip: Use GeekOBD APP to monitor real-time data during this diagnostic step for accurate results and professional-grade analysis.
Step 4: Step 4: System function test - After repairs, verify the proper operation of the thermostat by checking engine temperatures and clearing codes (10-15 minutes)

Step 4: System function test - After repairs, verify the proper operation of the thermostat by checking engine temperatures and clearing codes (10-15 minutes).

GeekOBD APP Tip: Use GeekOBD APP to monitor real-time data during this diagnostic step for accurate results and professional-grade analysis.
Step 5: Step 5: Road test verification - Drive the vehicle under various conditions to confirm the repair's success and ensure no additional codes arise (15-20 minutes)

Step 5: Road test verification - Drive the vehicle under various conditions to confirm the repair's success and ensure no additional codes arise (15-20 minutes).

GeekOBD APP Tip: Use GeekOBD APP to monitor real-time data during this diagnostic step for accurate results and professional-grade analysis.

Important Notes

  • Always verify the repair with GeekOBD APP after completing diagnostic steps
  • Clear codes and test drive to ensure the problem is resolved
  • Address underlying causes to prevent code recurrence

Real Repair Case Studies

Case Study 1: Thermostat Replacement on 2017 Honda Accord

Vehicle: 2017 Honda Accord, 75,000 miles

Problem: Customer reported fluctuating engine temperature and check engine light.

Diagnosis: Performed a diagnostic scan with GeekOBD APP which returned a P0591 code. Inspected the thermostat and wiring.

Solution: Replaced the faulty thermostat and gasket, topped off the coolant.

Cost: $220 (including $150 for the thermostat and $70 for labor)

Result: Temperature readings stabilized, and the check engine light was cleared.

Case Study 2: Wiring Repair on 2016 Toyota Camry

Vehicle: 2016 Toyota Camry, 60,000 miles

Problem: Customer experienced overheating and a persistent check engine light.

Diagnosis: Diagnostic scan revealed a P0591 code. Inspected wiring and found corrosion.

Solution: Repaired the damaged wiring harness and secured connections.

Cost: $120 (including $75 for wiring and $45 for labor)

Result: Vehicle returned to normal operating temperature, and the check engine light was resolved.

Diagnose P0591

Use GeekOBD APP for professional diagnosis!

  • Real-time data monitoring
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  • Step-by-step repair guidance
  • Professional-grade analysis
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Code Information

Code: P0591
System: Powertrain (Engine, Transmission, Emissions)
Severity: HIGH
Category: Engine Codes