Transmission

P0734 — Gear 4 Incorrect Ratio

Severity: medium Drive with care, to a shop

What P0734 means

The transmission control module compares input and output shaft speeds to calculate the actual gear ratio. In 4th gear that ratio must match a specified value. P0734 is set when the calculated ratio is outside the allowed range, which points to slipping or a gear that did not engage properly.

Symptoms

  • Check Engine light on, sometimes with the transmission in limp mode
  • Engine revs high on the highway without matching speed
  • No 4th gear or 4th gear drops out
  • Harsh or flared shift into 4th
  • Worse fuel economy
  • Overheated transmission or burnt fluid smell

Possible causes

  1. Low or degraded automatic transmission fluid (ATF)
  2. Worn or slipping 4th gear clutch or band
  3. Faulty shift solenoids or valve body
  4. Failed input or output speed sensor
  5. Faulty transmission range (TR) sensor or switch
  6. Damaged wiring, poor connector contact or bad ground
  7. Internal mechanical transmission fault

How to diagnose

  1. Scan all codes and freeze frame data and look for other transmission codes
  2. Check ATF level and condition: color, smell, metal debris
  3. Inspect transmission wiring and connectors for damage, corrosion and leaks
  4. Check input and output speed sensors and the range sensor in live data
  5. Test the shift solenoids for resistance and supply voltage
  6. Compare commanded and actual gear ratio and slip in 4th gear using live data
  7. Measure line pressure and, if needed, drop the pan and inspect it
  8. Check for a transmission control module software update

Common fixes

  • Top off or replace ATF and the filter
  • Replace a faulty speed or range sensor
  • Repair wiring and connectors
  • Replace solenoids or repair the valve body
  • Rebuild the transmission: clutches, band, seals
  • Update the control module software

P0734 on different brands

Ford · manuals
Ford documents P0734:00 (no sub type) in its 2024-2025 gasoline engine monitor strategy as incorrect gear 4 ratio; it identifies the detected monitor condition, not a confirmed failed component.

Questions and answers

Can I drive with code P0734?

Only briefly and gently to get to a shop. Driving long with slipping can seriously damage the transmission.

What should I check first for P0734?

Check the ATF level and condition, then the wiring and speed sensors. These are the simplest and cheapest checks and often reveal the cause.

Will clearing the code fix it?

The code may go away for a while, but it will return if the cause remains. Find and repair the underlying fault first.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.