P0735 Gear 5 Incorrect Ratio: Causes, Symptoms, and Fixes

The P0735 error code, also known as “Gear 5 Incorrect Ratio,” indicates a problem with your vehicle’s transmission. Specifically, it means the transmission control module (TCM) has detected an issue with the gear ratio in fifth gear. This article will delve into the causes, symptoms, diagnosis, and potential fixes for this common transmission problem.

Understanding the P0735 Code

The TCM constantly monitors the speed sensors in your transmission to ensure the correct gear ratio for each gear. When shifting into fifth gear, the TCM expects a specific relationship between the input and output shaft speeds. If this ratio is incorrect, the P0735 code is triggered and stored in the TCM’s memory. This discrepancy signifies that the actual gear ratio doesn’t match the expected ratio programmed into the TCM.

Common Causes of P0735 Gear 5 Incorrect Ratio

Several factors can contribute to a P0735 code. Here are some of the most common culprits:

Mechanical Problems Within the Transmission:

• Worn or Damaged Gears: Physical damage to the gears in the transmission can prevent them from engaging correctly, leading to an incorrect gear ratio.
• Faulty Shift Solenoids: These electromechanical components control fluid flow within the transmission to engage different gears. A malfunctioning solenoid can disrupt proper shifting.
• Worn Clutch Packs: Clutch packs engage and disengage gears. Worn or damaged clutches can lead to slippage and incorrect gear ratios.
• Low or Contaminated Transmission Fluid: Insufficient fluid or fluid contaminated with debris can hinder proper lubrication and hydraulic pressure, affecting gear engagement.

Electronic and Control System Issues:

• Malfunctioning TCM: A faulty TCM might misinterpret sensor data or send incorrect signals to the transmission, resulting in the P0735 code.
• Wiring Harness Problems: Damaged or corroded wiring in the transmission harness can disrupt communication between the TCM and the transmission components.
• Sensor Issues: Faulty input or output speed sensors can provide inaccurate data to the TCM, leading to an incorrect diagnosis of the gear ratio.

Symptoms of a P0735 Code

Recognizing the symptoms of a P0735 code can help you address the issue promptly. Common symptoms include:

• Illuminated Check Engine Light: This is often the first sign of a problem.
• Problems Shifting into or out of Fifth Gear: You might experience difficulty engaging fifth gear or a harsh shift when trying to do so.
• Slipping Transmission: The transmission might slip out of fifth gear while driving.
• Reduced Fuel Economy: An incorrect gear ratio can lead to engine inefficiency and increased fuel consumption.
• Limp Mode: In some cases, the vehicle might enter “limp mode” to prevent further damage, limiting speed and acceleration.

Diagnosing the P0735 Code

Diagnosing a P0735 code typically involves the following steps:

1. Retrieve the Code: Use an OBD-II scanner to read the stored trouble codes from the TCM.
2. Inspect Transmission Fluid: Check the fluid level and condition. Low or dirty fluid can indicate a problem.
3. Check Wiring and Connectors: Inspect the transmission wiring harness for damage, loose connections, or corrosion.
4. Test Sensors: Use a multimeter or specialized diagnostic equipment to test the functionality of the input and output speed sensors.
5. Evaluate Solenoid Operation: Test the shift solenoids using a scan tool or multimeter to ensure they are operating correctly.

Fixing the P0735 Code

The repair for a P0735 code depends entirely on the underlying cause:

• Fluid Change and Filter Replacement: If the fluid is low or dirty, a fluid change and filter replacement might resolve the issue.
• Wiring Repair: Damaged or corroded wiring will need to be repaired or replaced.
• Sensor Replacement: Faulty speed sensors need to be replaced.
• Solenoid Replacement: Malfunctioning solenoids should be replaced.
• Transmission Rebuild or Replacement: In severe cases involving internal damage to gears or clutch packs, a transmission rebuild or replacement might be necessary.

Conclusion

The P0735 “Gear 5 Incorrect Ratio” code signifies a potentially serious transmission problem. Early diagnosis and repair are crucial to prevent further damage and costly repairs. While some fixes might be simple, such as a fluid change, others can be complex and require professional expertise. If you encounter this code, it’s recommended to consult with a qualified mechanic for accurate diagnosis and appropriate repair.