For automotive technicians and DIY enthusiasts delving into vehicle diagnostics, understanding OBD-II error codes is crucial. Among these, the Eobd/obdii Error P0735, signaling a “Gear 5 Incorrect Ratio,” points to potential issues within the automatic transmission system. This article, crafted for professionals and knowledgeable car owners, will dissect this code, exploring its meaning, symptoms, causes, and diagnostic pathways, ensuring a comprehensive understanding and effective troubleshooting.
Understanding the P0735 Code: Gear 5 Incorrect Ratio
The P0735 diagnostic trouble code is a generic OBD-II powertrain code, meaning it can occur in a wide range of vehicles manufactured from 1996 onwards equipped with automatic transmissions. This code indicates that the vehicle’s Powertrain Control Module (PCM) or Transmission Control Module (TCM) has detected a discrepancy between the expected and actual gear ratio when the transmission is in 5th gear.
Modern automatic transmissions rely on precise gear ratios to optimize engine performance and driving efficiency across various speeds. The system uses sensors to monitor engine speed and transmission output speed, calculating the gear ratio. When the computer commands the transmission to shift into 5th gear, it expects a specific ratio. If the calculated ratio deviates significantly from the programmed value, the P0735 code is triggered, and the Check Engine Light illuminates.
It’s important to note that P0735 is part of a family of related codes (P0730, P0731, P0732, P0733, P0734, P0736) that indicate incorrect gear ratios in different gears. If multiple transmission codes are present, it is advisable to address those first before focusing on the P0735 error.
Symptoms Indicating a P0735 Error
When the P0735 code is active, drivers may observe several symptoms, which can vary in severity depending on the underlying cause:
- Illuminated Check Engine Light: This is the most immediate and common symptom, alerting the driver to a detected issue.
- Delayed or Absent 5th Gear Shift: The transmission may hesitate or fail to shift into 5th gear, especially noticeable at higher speeds.
- Transmission Slipping: The transmission might slip out of gear or exhibit a lack of power delivery, particularly in 5th gear.
- Reduced Fuel Economy: Inefficient gear shifting and potential slippage can lead to decreased fuel efficiency.
Potential Causes Behind the P0735 Code
Several factors can contribute to the P0735 error code. Identifying the root cause is crucial for effective repair. Common culprits include:
- Low or Contaminated Transmission Fluid: Insufficient or degraded transmission fluid can impair hydraulic pressure and lubrication, affecting gear shifts.
- Internal Mechanical Transmission Failure: Worn or damaged internal components like clutches, bands, or gears within the transmission can cause incorrect gear ratios.
- Internal Blockage in Transmission Main Control: Obstructions in the valve body or fluid passages can disrupt hydraulic control and gear selection.
- Faulty Shift Solenoid: Malfunctioning shift solenoids, responsible for controlling fluid flow to engage specific gears, can lead to incorrect gear ratios.
- Faulty Transmission Control Module (TCM): Though less common, a malfunctioning TCM can send incorrect signals or misinterpret sensor data, resulting in gear ratio errors.
Diagnosing and Repairing the P0735 Error
Diagnosing P0735 requires a systematic approach, often involving specialized tools and knowledge of automatic transmission systems. Here are recommended diagnostic and repair steps:
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Initial Inspection: Fluid Level and Condition: Begin by checking the transmission fluid level and condition. Low fluid or dirty, burnt fluid is a common issue and should be addressed first. Replenish or replace the fluid as necessary and re-evaluate.
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Test Drive and Gear Engagement: If fluid levels are adequate, perform a test drive to confirm if the transmission is indeed shifting into 5th gear. Observe for delayed shifts or slipping during the attempt to engage 5th gear.
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Shift Solenoid Testing: Shift solenoids control the hydraulic pressure to engage specific gears. While electrical issues with solenoids often trigger specific solenoid codes, a blockage or internal fault might contribute to a P0735. Testing solenoid functionality and circuits may be necessary.
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Advanced Diagnostic Scan Tool: Utilize an advanced diagnostic scan tool to monitor transmission parameters in real-time. This allows technicians to observe commanded gear versus actual gear, engine speed, and transmission output speed, helping pinpoint discrepancies.
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Internal Transmission Inspection and Repair: If external factors are ruled out, internal mechanical issues within the transmission become suspect. This may require transmission disassembly, inspection of clutches, bands, valve body, and other internal components. Repairing internal transmission faults often necessitates specialized skills and tools.
Note: Addressing P0735 often requires a solid understanding of automatic transmission operation and, in many cases, professional expertise. Consulting a factory service manual for vehicle-specific diagnostic procedures is highly recommended.
Conclusion
The eobd/obdii error p0735 indicates a “Gear 5 Incorrect Ratio,” signaling a potential malfunction within the automatic transmission’s ability to correctly engage 5th gear. Troubleshooting this code effectively involves a combination of systematic diagnostics, fluid checks, electronic testing, and potentially internal transmission inspection. By understanding the symptoms, potential causes, and diagnostic steps, technicians can accurately address the P0735 code, restoring optimal vehicle performance and transmission reliability. For further assistance and shared experiences, consider exploring online automotive repair forums where professionals and enthusiasts discuss complex diagnostic challenges like the P0735 error.
