P0731 Infiniti Code - 1st. Gear Malfunction
Quick Answer
This diagnosis monitors actual gear position by checking the torque converter slip ratio calculated by Transmission Control Module (TCM) as follows: Torque converter slip ratio = A x C/B A: Output shaft revolution signal from revolution sensor B: Engine speed signal from Engine Control Module (ECM) C: Gear ratio determined as gear position which TCM supposes If the actual gear position is higher than the position (1st) supposed by TCM, the slip ratio will be more than normal. Common causes include Low transmission fluid level, Dirty transmission fluid, Shift solenoids. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.
- What it means
- P0731 Infiniti indicates 1st. Gear Malfunction.
- Common causes
- Common causes include Low transmission fluid level, Dirty transmission fluid, Shift solenoids.
- Severity
- High - diagnose this code as soon as possible.
- Can I drive?
- Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.
Code P0731 Infiniti Description
Torque converter slip ratio = A x C/B
A: Output shaft revolution signal from revolution sensor
B: Engine speed signal from Engine Control Module (ECM)
C: Gear ratio determined as gear position which TCM supposes
If the actual gear position is higher than the position (1st) supposed by TCM, the slip ratio will be more than normal. In case the ratio exceeds the specified value, TCM judges this diagnosis malfunction.
What are the Possible Causes of the DTC P0731 Infiniti?
- Low transmission fluid level
- Dirty transmission fluid
- Shift solenoids
- Transmission mechanical problems
- Transmission hydraulic control circuit
How to Fix the DTC P0731 Infiniti?
Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.
Code Tech Notes
What is the Cost to Diagnose the Code?
Labor: 1.0
To diagnose the P0731 Infiniti code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.
Need more information about the P0731 Infiniti code?
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Need Help with the Code?
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Frequently Asked Questions about P0731 Infiniti Code
1. What does the OBDII code P0731 mean on an Infiniti?
P0731 indicates a "1st Gear Ratio Incorrect" fault, meaning the transmission control module (TCM) has detected a mismatch between the expected and actual gear ratio for 1st gear.
2. What are the common symptoms of code P0731 in an Infiniti?
Symptoms may include difficulty shifting into or out of 1st gear, slipping in 1st gear, reduced acceleration, poor fuel economy, or the transmission going into limp mode.
3. What causes the P0731 code on an Infiniti?
Common causes include low or contaminated transmission fluid, a faulty shift solenoid, a malfunctioning transmission speed sensor, or internal transmission damage such as worn clutches or bands.
4. How can I fix the P0731 code on my Infiniti?
Start by checking and replacing the transmission fluid if needed. If the issue persists, inspect the shift solenoids, speed sensors, and wiring. Further diagnosis may require a professional to check for internal transmission damage.
5. Can driving with the P0731 code damage my Infiniti's transmission?
Yes, continuing to drive with this code can cause further damage to the transmission, especially if it involves slipping gears or overheating.
6. How do I know if my transmission fluid is causing the P0731 code?
Check the fluid level and condition. Low, dark, or burnt-smelling fluid can cause shifting issues and may trigger the P0731 code.
7. Is P0731 a serious issue for my Infiniti?
Yes, P0731 indicates a transmission problem that should be addressed promptly to avoid further damage or unsafe driving conditions.
8. Can a faulty speed sensor trigger the P0731 code on an Infiniti?
Yes, a malfunctioning transmission speed sensor can send incorrect data to the TCM, causing it to misinterpret the gear ratio and trigger the P0731 code.
9. Do I need to replace the transmission to fix the P0731 code?
Not necessarily. Many P0731 issues can be resolved by addressing specific components like solenoids, sensors, or fluid problems. However, severe internal damage may require a rebuild or replacement.
10. Can I diagnose the P0731 code on my Infiniti myself?
You can start by checking the transmission fluid, scanning for additional codes, and inspecting wiring and connectors. Advanced diagnosis, such as testing solenoids or internal components, may require professional tools and expertise.
Discuss the causes and fixes for P0731 Infiniti OBDII Code
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Why is it so hard to find out where the transmission fluid is under the hood of the car?
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Finding the transmission fluid dipstick or fill port in an Infiniti (and some other modern vehicles) can be challenging because many manufacturers have moved away from providing easy access under the hood. Infiniti and other manufacturers often aim to prevent overfilling or contamination by requiring special tools or dealer assistance for checking and filling the fluid.
In many newer Infiniti models, transmission fluid is checked via a sealed or closed system, which typically requires lifting the car and accessing a fill/check port located on the transmission itself rather than under the hood. This design reflects the push towards "maintenance-free" transmissions that are factory-filled and intended to need less frequent checks.
If you’re not finding a dipstick or fill tube under the hood, consult the owner’s manual or consider visiting a mechanic or dealership for help with transmission fluid checks or service.
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