What it means
The transmission control module detected an incorrect ratio while fifth gear was commanded or expected. The code alone does not confirm slipping or identify the cause.
At a glance
- Usually lights the check-engine light
- The engine or gearbox may go into limp mode
How it works
The TCM checks fifth gear by comparing input and output speed signals with the ratio expected when fifth gear is commanded. P0735 sets when that ratio is outside the allowed range, which may reflect a fifth-gear apply problem or an unreliable speed signal.
Common causes
Most likely first.
- Low or degraded transmission fluid
- Worn or damaged fifth-gear clutch or friction elements
- Hydraulic pressure loss or valve body fault
- Fault in a speed sensor or its wiring
Symptoms
- Check engine or transmission warning light on
- Harsh, delayed, or missing shifts
- Possible limp mode (locked in one gear)
- Slipping or shuddering during gear changes
How to diagnose it
- Record freeze-frame data and related transmission codes to confirm the speed, load, and commanded gear when the fifth-gear ratio fault occurred.
- Check fluid level and condition using the specified procedure, since low or degraded fluid can prevent reliable fifth-gear clutch application.
- Inspect speed-sensor wiring and connectors for damage, corrosion, contamination, or poor contact.
- Compare commanded gear with live input and output speed data during a controlled drive that reaches fifth gear.
- Test speed-sensor circuits and hydraulic pressure to the manufacturer's specification, then assess fifth-gear friction elements and valve-body operation if those checks pass.
Common fixes
- Correct low fluid or service degraded fluid to the vehicle's requirements.
- Repair damaged speed-sensor wiring or connector contacts.
- Replace a speed sensor if testing confirms an inaccurate signal.
- Repair a confirmed valve-body or hydraulic pressure fault affecting fifth gear.
- Repair worn or damaged fifth-gear friction elements if internal inspection confirms the fault.
Can I keep driving?
Avoid highway trips, towing, and hard acceleration if fifth gear slips or the transmission shudders; have it diagnosed promptly. Continued slipping can overheat the fluid and damage the fifth-gear components.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.