Quick Answer
P0840 means: P0840 signifies a problem with the transmission fluid pressure sensor or switch A circuit.
Can I drive with P0840? Immediate attention is recommended to avoid potential transmission damage.
Common Questions
What does P0840 mean and how does it affect my car?
The P0840 code indicates a malfunction in the transmission fluid pressure sensor circuit. This can lead to poor shifting performance and can indicate potential issues with your vehicle's transmission. If not addressed, it may lead to more severe problems and costly repairs.
What are the most common causes of P0840 and how much does it cost to fix?
The most common causes of P0840 include a faulty transmission fluid pressure sensor and damaged wiring, with repair costs ranging from $100 to $300 depending on the specific issue and parts needed.
Can I drive my car with P0840 or should I stop immediately?
While you may be able to drive with a P0840 code, it is not advisable. Continuing to drive can lead to further transmission damage and safety concerns, so addressing the issue as soon as possible is crucial.
How can I diagnose P0840 myself using GeekOBD APP?
To diagnose P0840, connect the GeekOBD APP to your vehicle's OBD2 port, retrieve the trouble codes, and check for freeze frame data. This will help you understand when the issue occurs and guide your troubleshooting process.
What vehicles are most commonly affected by P0840?
Common vehicles affected by P0840 include the 2005-2010 Honda Accord, the 2006-2011 Chevrolet Malibu, and various models from Ford and Toyota from the same era. Always check for specific recalls or Technical Service Bulletins (TSBs) related to your vehicle.
How can I prevent P0840 from happening again?
Regular maintenance, including timely transmission fluid changes and inspections, can help prevent P0840 from occurring in the future. Ensure that any transmission repairs are performed by a qualified technician.
What is P0840?
The P0840 diagnostic trouble code (DTC) indicates that there is a problem with the transmission fluid pressure sensor or switch A circuit. This sensor plays a vital role in regulating the transmission's hydraulic pressure, which is essential for smooth gear shifts. When the sensor fails or the circuit experiences issues, it can lead to erratic shifting, reduced fuel efficiency, and even transmission damage over time. Commonly found in vehicles like the 2005-2010 Honda Accord and the 2006-2011 Chevrolet Malibu, P0840 is often accompanied by other codes related to transmission performance. If your vehicle’s check engine light is illuminated and you notice symptoms like delayed shifting or harsh transitions between gears, it could be a sign that the P0840 code has triggered. Ignoring this code can lead to more severe transmission problems and costly repairs, so it’s crucial to diagnose and address the issue promptly. Regular maintenance, including transmission fluid changes and inspections, can help prevent this code from appearing.
System: P - Powertrain (Engine, Transmission, Emissions)
Symptoms
Common symptoms when P0840 is present:
- Check engine light stays on constantly, indicating an issue that needs immediate attention.
- Engine hesitates during acceleration, making driving experience frustrating and potentially unsafe.
- Fuel economy decreased by 10-15%, leading to increased costs at the pump.
- Unusual transmission behavior such as slipping or harsh shifting, affecting overall vehicle performance.
- Gear shifting occurs later than expected, causing potential safety concerns during driving.
Possible Causes
Most common causes of P0840 (ordered by frequency):
- Faulty transmission fluid pressure sensor, which is the most common cause at approximately 70%. This can result from wear and tear over time or exposure to extreme temperatures.
- Damaged wiring or connectors associated with the sensor, which can lead to intermittently poor connections and erratic sensor readings.
- Low transmission fluid levels due to leaks or inadequate maintenance, which can cause the sensor to report incorrect readings.
- Malfunctioning transmission control module (TCM) that may misinterpret sensor signals, leading to improper transmission behavior.
- Rare but possible: Internal transmission failure that can cause abnormal pressure readings, requiring significant repairs.
P0840 Repair Costs
Cost Breakdown by Repair Type
Sensor Replacement
Replacing the faulty transmission fluid pressure sensor will rectify the P0840 code.
- Total: $150 - $300
- Success rate: 85%
Wiring Repair
Repairing damaged wiring or connectors associated with the sensor.
- Total: $100 - $250
- Success rate: 90%
Fluid Change
Performing a transmission fluid change if low levels are detected.
- Total: $80 - $150
- Success rate: 75%
Money-Saving Tips for P0840
- 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 P0840 Diagnosis Process
Follow these systematic steps to accurately diagnose P0840. 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 (5-10 minutes)
Step 1: Initial visual inspection - Check for obvious signs like damaged wiring, loose connections, or corrosion (5-10 minutes).
Step 2: Step 2: OBD2 scan with GeekOBD APP - Retrieve all codes and freeze frame data to understand the fault context (10-15 minutes)
Step 2: OBD2 scan with GeekOBD APP - Retrieve all codes and freeze frame data to understand the fault context (10-15 minutes).
Step 3: Step 3: Component testing - Use multimeter or specific diagnostic tools to test suspected components (20-30 minutes)
Step 3: Component testing - Use multimeter or specific diagnostic tools to test suspected components (20-30 minutes).
Step 4: Step 4: System function test - Verify proper operation after repairs and clear codes (10-15 minutes)
Step 4: System function test - Verify proper operation after repairs and clear codes (10-15 minutes).
Step 5: Step 5: Road test verification - Drive vehicle under various conditions to confirm repair success (15-20 minutes)
Step 5: Road test verification - Drive vehicle under various conditions to confirm repair success (15-20 minutes).
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 Pressure Sensor Replacement in Honda Accord
Vehicle: 2010 Honda Accord, 85,000 miles
Problem: Customer reported check engine light and rough shifting.
Diagnosis: Diagnostic scan revealed P0840 along with low transmission fluid levels.
Solution: Replaced the faulty transmission fluid pressure sensor and performed a fluid change.
Cost: $250 (sensor: $150, fluid: $100)
Result: The check engine light turned off, and the vehicle shifted smoothly afterward.
Case Study 2: Wiring Issue Repair in Chevrolet Malibu
Vehicle: 2007 Chevrolet Malibu, 95,000 miles
Problem: Customer experienced delayed shifting and check engine light activation.
Diagnosis: Found damaged wiring leading to the transmission fluid pressure sensor.
Solution: Repaired the wiring and cleared the codes.
Cost: $180 (wiring repair: $80, diagnostic fee: $100)
Result: The vehicle exhibited normal shifting behavior and the code did not return.