Fault code P0734 – a step-by-step guide to diagnosing and fixing it

Error code P0734 is displayed and the check engine light is on - what does this mean?

The OBD system detects an error in 4th gear of the automatic transmission where the expected transmission ratio is not achieved. This DTC P0734 affects the transmission control unit and can occur with both mechanical and electronic problems.

What can cause this error code?

• Defective clutches or brake bands in 4th gear
• Worn transmission fluid or low fluid level
• Blocked or defective solenoid valves in the valve body
• Damaged seals or internal leaks
• Defective transmission control module (TCM)
• Faulty speed sensors
• Mechanical wear of the planetary gears
• Clogged transmission filter
• Loose or corroded electrical connections

What symptoms occur in parallel with fault code P0734?

• Shifting problems: The transmission does not shift into 4th gear or slips
• Jerking: Noticeable vibrations when trying to shift into 4th gear
• High engine speed: Engine revs unusually high at highway speeds
• Emergency running program: Transmission gets stuck in the lower gears
• Delayed shifting: Unusually late or hard shifting
• Overheating: Transmission temperature rises due to slipping

How can the problem with error code P0734 be rectified?

• The repair usually requires professional diagnosis, as it involves complex transmission technology.
• Change transmission fluid and filter if dirty or at low level
• Replace defective solenoid valves in the valve body or overhaul the entire valve body
• Check transmission control unit and replace or reprogram if defective
• Test speed sensors and replace faulty sensors
• Check electrical connections and wiring harness for damage and repair
• In the event of mechanical wear, dismantle gearbox and replace clutches/brake bands
• Complete transmission overhaul or replacement transmission in the event of severe damage