P0735 - Gear 5 Incorrect Ratio

Introduction:

The diagnostic trouble code (DTC) P0735 indicates that the transmission control module (TCM) or powertrain control module (PCM) has detected an incorrect gear ratio in the fifth gear of your automatic transmission. This means the calculated ratio of input shaft speed to output shaft speed in fifth gear doesn't match the expected or programmed value. A P0735 code signals a potentially serious problem within the transmission that needs immediate attention to prevent further damage.

Table: P0735 - Gear 5 Incorrect Ratio Breakdown

Detailed Explanations:

Code Definition: The P0735 code is triggered when the TCM/PCM calculates that the ratio between the input speed of the transmission and the output speed of the transmission in fifth gear is outside of the acceptable range programmed into the module. This indicates a problem with the transmission's ability to properly engage and maintain fifth gear.

Symptoms: The symptoms of a P0735 code can vary depending on the severity of the problem. The most common symptom is the illumination of the Check Engine Light (CEL). Other symptoms may include transmission slipping in fifth gear, difficulty shifting into or out of fifth gear, being stuck in a lower gear, reduced fuel economy, unusual noises from the transmission, harsh or erratic shifting, and in some cases, the vehicle may enter limp mode to protect the transmission from further damage.

Potential Causes:

• Low transmission fluid level or contaminated fluid: The transmission relies on fluid for lubrication, cooling, and hydraulic pressure. Low fluid levels can lead to insufficient lubrication, causing clutches to slip. Contaminated fluid can also reduce its lubricating properties and damage internal components.
• Faulty shift solenoid(s): Shift solenoids are electrically operated valves that control the flow of transmission fluid to engage and disengage gears. A malfunctioning solenoid can prevent proper gear engagement, leading to an incorrect gear ratio.
• Damaged or worn clutches: The clutches within the transmission are responsible for engaging and disengaging gears. Over time, these clutches can wear down or become damaged, causing them to slip and resulting in an incorrect gear ratio.
• Internal transmission damage: Broken gears, damaged bearings, or other internal mechanical failures can disrupt the gear ratios, triggering the P0735 code. This often requires a complete transmission overhaul or replacement.
• Faulty transmission control module (TCM): The TCM is responsible for controlling the operation of the transmission. A faulty TCM can send incorrect signals to the solenoids, leading to incorrect gear selection and the P0735 code.
• Faulty powertrain control module (PCM): The PCM may also be involved in transmission control, especially in newer vehicles. A malfunction can cause incorrect shifting.
• Damaged or worn transmission bands: In some older transmissions, bands are used to hold certain gears while others are engaged. Worn or damaged bands can cause slippage, leading to the P0735 code.
• Valve body issues: The valve body directs fluid to the correct parts of the transmission. Clogging or damage can cause shifting problems and trigger the code.
• Wiring harness or connector problems: Damaged, corroded, or loose wiring or connectors can disrupt the signals between the TCM/PCM and the transmission, leading to incorrect gear selection and the P0735 code.
• Incorrect transmission fluid type: Using the wrong type of fluid can damage the transmission and cause shifting problems. Always use the fluid specified in your vehicle's owner's manual.
• Mechanical failure of the 5th gear set: The 5th gear components themselves (gear, synchro, etc.) may be physically damaged, preventing proper engagement.
• Input/Output speed sensor failure: If either the input or output speed sensor is providing incorrect data, the TCM/PCM will miscalculate the gear ratio, even if the transmission is mechanically sound.

Diagnostic Steps:

• Check transmission fluid level and condition: Begin by checking the transmission fluid level using the dipstick (if equipped). Ensure the fluid is at the correct level and that it doesn't smell burnt or contain debris. Low or contaminated fluid is a common cause of transmission problems.
• Scan for other DTCs: Use an OBD-II scanner to check for any other DTCs related to the transmission or engine. Address any other codes before focusing on P0735, as they may be contributing to the problem.
• Inspect wiring and connectors: Visually inspect the wiring harness and connectors associated with the transmission for any signs of damage, corrosion, or loose connections. Repair or replace any damaged wiring or connectors.
• Test shift solenoids: Use a multimeter or scan tool to test the resistance and operation of the shift solenoids. Refer to the vehicle's service manual for the correct testing procedures and specifications.
• Monitor transmission data with a scan tool: Use a scan tool to monitor the input shaft speed, output shaft speed, and gear selection data while driving the vehicle. This can help identify discrepancies in the gear ratio.
• Perform a transmission flush and filter replacement: If the transmission fluid is contaminated, a transmission flush and filter replacement can help remove contaminants and improve transmission performance.
• Perform a stall test: This test can help diagnose slipping clutches. It involves applying the brakes and accelerating the engine to a certain RPM. Abnormal results indicate a problem with the clutches. Consult a repair manual for the correct procedure and interpretation of the results.
• Check for TSBs (Technical Service Bulletins): Check for any TSBs issued by the vehicle manufacturer that address the P0735 code or related transmission problems. TSBs may provide specific diagnostic and repair procedures.
• Consult a qualified transmission technician: If you are not comfortable performing these diagnostic steps, it is best to seek professional help from a qualified transmission technician. They have the specialized tools and knowledge to diagnose and repair complex transmission problems.

Possible Repairs:

• Transmission fluid change and filter replacement: If the fluid is low or contaminated, a fluid change and filter replacement may resolve the problem.
• Shift solenoid replacement: If a shift solenoid is faulty, it will need to be replaced.
• Clutch replacement: If the clutches are worn or damaged, they will need to be replaced. This typically requires a transmission overhaul.
• Valve body repair or replacement: If the valve body is damaged or clogged, it may need to be repaired or replaced.
• Transmission overhaul or replacement: If there is significant internal damage to the transmission, an overhaul or replacement may be necessary.
• Wiring harness repair or replacement: Repair any damaged wiring or replace the entire harness if necessary.
• TCM/PCM reprogramming or replacement: In rare cases, the TCM or PCM may be faulty and need to be reprogrammed or replaced.
• Input/Output speed sensor replacement: If one or both speed sensors are faulty, replacing them might solve the problem.
• Repair or replacement of damaged gears or other internal transmission components: This is usually part of a transmission overhaul.

Severity: The severity of a P0735 code is considered high. Continuing to drive with this code can lead to significant transmission damage and costly repairs. It's crucial to address the problem as soon as possible to prevent further damage.

Frequently Asked Questions:

• Can I drive with a P0735 code? No, it's not recommended. Driving with a P0735 code can cause further damage to your transmission.

• Is the P0735 code serious? Yes, it indicates a problem with the transmission that needs immediate attention.

• How much does it cost to fix a P0735 code? The cost can vary widely depending on the cause of the problem. It could range from a simple fluid change to a complete transmission overhaul, costing anywhere from a few hundred to several thousand dollars.

• Can low transmission fluid cause a P0735 code? Yes, low transmission fluid is a common cause of transmission problems, including the P0735 code.

• Can a bad shift solenoid cause a P0735 code? Yes, a faulty shift solenoid can prevent proper gear engagement, leading to an incorrect gear ratio and the P0735 code.

Conclusion:

The P0735 code signals a problem with the transmission's ability to properly engage fifth gear. Prompt diagnosis and repair are essential to prevent further damage and costly repairs. Always consult a qualified technician if you're not comfortable performing the diagnostic and repair procedures yourself.