P0734
Gear 4 Incorrect Ratio
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P0734 indicates the Powertrain Control Module has detected an incorrect gear ratio when the transmission is in fourth gear. The PCM calculates the expected ratio between input and output shaft speeds for fourth gear, and when the actual ratio falls outside the acceptable range, this code is triggered.
Fourth gear is typically the overdrive gear in a 4-speed automatic, so this problem is most noticeable on the highway. You may notice your engine RPMs staying higher than normal at cruising speed, reduced fuel economy, or the transmission hunting back and forth between third and fourth gear. The vehicle may also feel like it loses power momentarily during the 3-4 shift.
Check your transmission fluid first — it's the most common and least expensive cause. If the fluid level is correct and the fluid appears clean and doesn't smell burnt, a professional diagnosis is the next step. A transmission technician can run pressure tests and solenoid tests to determine whether the fault is with a solenoid, sensor, wiring, or internal mechanical components. Don't ignore this code, as continued driving with a slipping gear accelerates wear on the transmission internals.
Severity
Symptoms
- •Slipping or harsh shift into fourth gear (overdrive)
- •RPMs remain higher than normal at highway speeds
- •Decreased highway fuel economy
- •Check Engine light illuminated
- •Vehicle may drop out of overdrive unexpectedly
Likely Causes
Insufficient or degraded fluid cannot maintain the hydraulic pressure needed to engage fourth gear properly, causing slippage and an incorrect ratio.
The overdrive clutch or band may be worn, preventing fourth gear from fully engaging and causing the PCM to detect ratio inconsistencies.
The solenoid controlling the 3-4 shift may be stuck, worn, or electrically faulty, preventing proper engagement of fourth gear.
Worn passages or stuck valves in the valve body can prevent adequate pressure from reaching the fourth gear circuit.
An intermittent or failing speed sensor can cause the PCM to miscalculate the gear ratio.
Estimated Cost
Professional Repair
Includes parts + labor
Common Fixes
- Perform transmission fluid and filter service
- Replace the shift solenoid
- Replace faulty speed sensor(s)
- Repair or replace the valve body
- Rebuild or replace the transmission
Shop Parts
Videos
Causes and Fixes P0734 Code: Gear 4 Incorrect Ratio
HVAC Mechanic
What is P0734 : Engine Error Code Causes Explained
Auto User Guide
💙 P0734 Code: CAUSES and SOLUTIONS【2025】💙
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