Transmission · Powertrain · generic (SAE-defined)
P0734: Gear 4 Incorrect Ratio
P0734 means the transmission computer detected that fourth gear is not delivering the expected speed ratio, which usually points to slipping in fourth or a speed sensor fault.
Standard title per SAE J2012 / ISO 15031-6 · Updated 2026-11-07 · By CarWhere Research
How P0734 sets
When fourth gear is commanded, the transmission control module (TCM) compares input speed divided by output speed with the fourth-gear ratio. If the result remains outside tolerance for a set time, it sets P0734. On four-speed transmissions this is often the overdrive gear; tolerances are manufacturer-specific.
Common causes of P0734
Roughly most likely first; the actual cause depends on the vehicle and needs testing to confirm.
- Low or burnt transmission fluid
- Worn overdrive or fourth-gear clutch or band
- Faulty shift solenoid or pressure control solenoid
- Valve body wear
- Leaking internal seals or servo
- Faulty input or output speed sensor
P0734 symptoms
- Check engine light on
- Engine speed rising at highway speed without acceleration
- Transmission will not shift into fourth
- Harsh 3-4 shift or flare
- Reduced fuel economy
How P0734 is diagnosed
- Read all transmission codes and record freeze frame data
- Check fluid level and condition
- Road test at cruising speed while graphing input, output and engine speeds
- Verify speed sensor accuracy
- Check solenoid and torque converter clutch operation
- Pressure-test or inspect internal components if needed
Typical fixes for P0734
- Correct fluid level or perform a fluid and filter service
- Replace the faulty solenoid
- Repair the valve body
- Replace a faulty speed sensor
- Rebuild or replace the transmission if fourth-gear components are worn
Replace parts only after testing confirms the cause — a code names the circuit or condition that failed a check, not necessarily the faulty part. We don’t publish per-repair prices; for what households actually spend on upkeep, see car repair costs.
Related codes & warning lights
P0734 FAQ
What does code P0734 mean?
P0734 means the transmission computer detected that fourth gear is not delivering the expected speed ratio, which usually points to slipping in fourth or a speed sensor fault. The standard definition is "Gear 4 Incorrect Ratio."
Can I drive with a P0734 code?
Avoid long trips and highway driving until it is checked. Fourth gear is often an overdrive or cruising gear, and slipping at steady speed can overheat the transmission.
Is fourth gear overdrive?
On many four-speed automatics it is. On transmissions with more gears, fourth may be a direct or intermediate gear, so the affected clutch varies by design.
Could a torque converter problem look like P0734?
A slipping torque converter clutch can cause engine speed changes at cruise, but it usually sets its own codes. Ratio codes compare shaft speeds inside the gear set.
Keep researching
More transmission codes
Sources
- SAE J2012 — Diagnostic Trouble Code Definitions (standard code titles)
- ISO 15031-6 — Road vehicles: communication between vehicle and external equipment for emissions-related diagnostics, Part 6: Diagnostic trouble code definitions
- U.S. EPA — Vehicle Emissions Inspection and Maintenance (I/M) programs
- U.S. EPA, 40 CFR 86.1806-17 — Federal onboard diagnostics requirements for light-duty vehicles
General information written by CarWhere Research, not a diagnosis of your vehicle. Manufacturers can add their own sub-definitions and test conditions; confirm with the factory service information for your year, make and model. Before paying for a repair, check NHTSA for open recalls and your warranty booklet: federal law requires an emissions warranty on major emission-control parts such as the catalytic converter and engine computer.