P0991 - Transmission Fluid Temperature Sensor Range/Performance Problem in Honda, Toyota, and More

Quick Answer

P0991 means: The P0991 code indicates a performance issue with the transmission fluid temperature sensor.

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

Can I drive with P0991? Immediate attention is recommended to prevent transmission damage.

Common Questions

What does P0991 mean and how does it affect my car?

The P0991 code signifies a problem with the transmission fluid temperature sensor, which can lead to poor transmission performance. If the sensor fails, the transmission may overheat, resulting in slipping or erratic shifting. This can ultimately lead to costly repairs if left unaddressed, affecting your vehicle's reliability and safety.

What are the most common causes of P0991 and how much does it cost to fix?

Common causes include a faulty transmission fluid temperature sensor, wiring issues, and low transmission fluid. Repair costs can range from $150 to $300 for sensor replacement, with wiring repairs costing about $100 to $200. It’s essential to diagnose the root cause accurately to avoid unnecessary repairs.

Can I drive my car with P0991 or should I stop immediately?

Driving with a P0991 code is not advisable as it can lead to severe transmission damage. If you notice symptoms like slipping or overheating, it’s best to stop driving and seek professional assistance to prevent further complications.

How can I diagnose P0991 myself using GeekOBD APP?

To diagnose P0991 with the GeekOBD APP, connect the device to your vehicle’s OBD2 port. Use the app to scan for trouble codes, retrieve freeze frame data, and monitor the sensor’s performance in real-time. Look for any abnormal temperature readings that may indicate a faulty sensor.

What vehicles are most commonly affected by P0991?

The P0991 code frequently appears in a variety of vehicles, particularly in the 2015-2018 Honda Civic, 2010-2015 Toyota Camry, and 2013-2017 Ford Focus. Each model may have specific recalls or technical service bulletins (TSBs) related to transmission issues, so checking with a dealer may be beneficial.

How can I prevent P0991 from happening again?

Preventive measures include regular transmission fluid changes, checking for leaks, and ensuring all electrical connections to the transmission are intact. Additionally, using high-quality transmission fluid and monitoring for early signs of transmission issues can help avoid future occurrences of the P0991 code.

What is P0991?

The P0991 diagnostic trouble code (DTC) indicates a range or performance issue with the transmission fluid temperature sensor. This sensor plays a crucial role in monitoring the temperature of the transmission fluid, which is vital for optimal transmission performance. When the engine control module (ECM) detects an out-of-range signal from this sensor, it triggers the P0991 code. A malfunctioning transmission fluid temperature sensor can result in various transmission issues, such as erratic shifting, overheating, and even potential transmission failure if not addressed promptly. Commonly found in vehicles such as the 2015-2018 Honda Civic, Toyota Camry, and Ford Focus, this code often appears alongside other transmission-related codes. Drivers may experience symptoms like slipping transmission, poor acceleration, or unexpected gear shifts. Ignoring this problem can lead to more severe complications, such as complete transmission breakdown, which can be costly to repair. Therefore, understanding the implications of a P0991 code is essential for maintaining your vehicle's transmission health and ensuring a smooth driving experience.

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

Symptoms

Common symptoms when P0991 is present:

  • Check engine light illuminates and stays on continuously, indicating a potential issue.
  • Transmission slips during acceleration, which can feel like a delay in power delivery.
  • Engine struggles to shift gears smoothly, often resulting in harsh or erratic shifting patterns.
  • Reduced fuel economy, which may drop by 10-20% due to increased engine load and inefficient transmission operation.
  • Unexpected overheating of the transmission, which can lead to further damage if not addressed.

Possible Causes

Most common causes of P0991 (ordered by frequency):

  1. Faulty transmission fluid temperature sensor (70% likelihood) - The most common issue arises when the sensor fails to accurately read fluid temperature, sending incorrect signals to the ECM.
  2. Wiring issues (15% likelihood) - Damaged or corroded wiring can disrupt the signal transmission from the sensor to the ECM, causing the code.
  3. Transmission fluid issues (10% likelihood) - Low fluid levels or degraded fluid can affect temperature readings and transmission performance.
  4. Faulty ECM (3% likelihood) - In rare cases, the engine control module itself may malfunction and misinterpret signals from the temperature sensor.
  5. Mechanical transmission problems (2% likelihood) - Issues such as slipping gears or internal damage can mimic the symptoms of a P0991 code.

P0991 Repair Costs

Cost Breakdown by Repair Type

Sensor Replacement

Replacing the faulty transmission fluid temperature sensor to restore accurate readings.

  • Total: $150 - $300
  • Success rate: 90%
Wiring Repair

Repairing or replacing damaged wiring that may be causing signal disruption.

  • Total: $100 - $200
  • Success rate: 85%
Transmission Fluid Change

Changing the transmission fluid to ensure optimal performance and temperature readings.

  • Total: $80 - $150
  • Success rate: 75%
Money-Saving Tips for P0991
  • 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 P0991 Diagnosis Process

Follow these systematic steps to accurately diagnose P0991. Each step builds on the previous one to ensure accurate diagnosis.

Step 1: Step 1: Initial visual inspection - Look for noticeable issues such as damaged wiring, loose connections, or signs of fluid leaks (5-10 minutes)

Step 1: Initial visual inspection - Look for noticeable issues such as damaged wiring, loose connections, or signs of fluid leaks (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 - Use the app to retrieve all trouble codes and freeze frame data to gain context for the fault (10-15 minutes)

Step 2: OBD2 scan with GeekOBD APP - Use the app to retrieve all trouble codes and freeze frame data to gain context for the fault (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 - Utilize a multimeter to test the voltage and resistance of the transmission fluid temperature sensor to ensure it operates within specifications (20-30 minutes)

Step 3: Component testing - Utilize a multimeter to test the voltage and resistance of the transmission fluid temperature sensor to ensure it operates within specifications (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 that the transmission operates correctly and clear the codes to reset the system (10-15 minutes)

Step 4: System function test - After repairs, verify that the transmission operates correctly and clear the codes to reset the system (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 that the transmission shifts smoothly and that no further codes appear (15-20 minutes)

Step 5: Road test verification - Drive the vehicle under various conditions to confirm that the transmission shifts smoothly and that no further codes appear (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: Transmission Fluid Sensor Replacement in a 2016 Honda Civic

Vehicle: 2016 Honda Civic, 45,000 miles

Problem: Customer reported check engine light on and rough shifting.

Diagnosis: Diagnostic scan revealed P0991 alongside P0700. Visual inspection showed a faulty sensor.

Solution: Replaced the faulty transmission fluid temperature sensor and cleared the codes.

Cost: $250 (sensor $150, labor $100)

Result: Vehicle returned to normal operation with smooth shifting and no further codes.

Case Study 2: Wiring Repair on a 2015 Toyota Camry

Vehicle: 2015 Toyota Camry, 60,000 miles

Problem: Customer experienced transmission slipping and overheating.

Diagnosis: P0991 code identified; wiring inspection revealed corroded connections.

Solution: Repaired the wiring and replaced damaged connectors to restore signal integrity.

Cost: $150 (wiring repair $75, labor $75)

Result: Transmission performance improved significantly with no further issues after repair.

Diagnose P0991

Use GeekOBD APP for professional diagnosis!

  • Real-time data monitoring
  • Advanced diagnostic features
  • Step-by-step repair guidance
  • Professional-grade analysis
Download GeekOBD APP Get MOBD Adapter

Code Information

Code: P0991
System: Powertrain (Engine, Transmission, Emissions)
Severity: HIGH
Category: Engine Codes