P0734 on BMW: How to Diagnose & Fix
Gear 4 Incorrect Ratio
4 BMW models · 5 documented issues · 2 critical · $500-$8,000 repair
P0734 on BMW by model: symptoms, diagnosis and fix
The 7-speed M-DCT dual-clutch transmission in F87 M2 models can develop mechatronics unit failures, causing harsh shifting, failure to engage gears, or transmission fault warnings. The issue is related to the solenoid pack and hydraulic valve body within the mechatronics sleeve.
Common Symptoms
- Harsh or delayed shifts
- Transmission malfunction warning
- Failure to engage gear
- Grinding noise during shifts
- Limp mode activation
- Check engine light
- Jerking at low speeds
How to Fix
Replace or rebuild the mechatronics unit. In some cases, a transmission adaptation reset via ISTA can resolve early-stage symptoms. Severe cases require full mechatronics replacement, which involves dropping the transmission. Fluid change every 30k miles helps extend life.
Sources for this issue (1)
The Getrag DCT (dual-clutch transmission) in the M2 and M2 Competition experiences clutch pack wear from aggressive driving, launches, and track use. The DCT has two clutches (odd and even gears) that wear over time. Symptoms include shuddering during low-speed acceleration, rough shifting, and slipping under hard acceleration. Track use and repeated launch control engagements accelerate wear. DCT fluid degradation also contributes to poor shift quality. This transmission is shared with M3/M4 and has similar failure patterns.
Common Symptoms
- Shuddering or judder when accelerating from a stop
- Rough or harsh shifting between gears
- Slipping sensation under hard acceleration
- Burning smell from transmission
- Check engine light with transmission codes
- Clutch slip warnings on iDrive
How to Fix
Replace DCT clutch pack ($4,000-6,000 parts + labor). Change DCT fluid every 30,000 miles with BMW-approved fluid to extend clutch life. Avoid excessive launch control use. Transmission adaptation reset via BMW software often improves shift quality temporarily. Some performance shops offer upgraded clutch packs for track use. Extended warranty coverage highly recommended for DCT-equipped M2s.
Sources for this issue (1)
The xDrive transfer case actuator motor in X1 models can fail, causing loss of all-wheel drive functionality. The electric motor that engages the front axle wears out or its internal gears strip. Failure is often sudden and accompanied by drivetrain warning messages.
Common Symptoms
- Drivetrain malfunction warning on dashboard
- 4x4 warning light illuminated
- Loss of power to front wheels
- Grinding or clicking noise from under vehicle
- Vehicle feels unstable in slippery conditions
- Reduced traction in snow or rain
How to Fix
Replace the transfer case actuator motor (also called the servo motor). The transfer case itself usually does not need replacement. Ensure the transfer case fluid is changed at the same time. Some owners report success with rebuilt actuators at lower cost.
Sources for this issue (1)
The Getrag DCT (dual-clutch transmission) in the M4 experiences clutch pack wear from aggressive driving, repeated launch control, and track use. The DCT has two clutches (odd and even gears) that wear over time. Symptoms include shuddering during low-speed acceleration, rough shifting, and slipping under hard acceleration. Track use and launch control dramatically accelerate wear. DCT fluid degradation also contributes to poor shift quality. Clutch replacement is expensive ($5,000-8,000) and considered a wear item on high-performance use.
Common Symptoms
- Shuddering or judder when accelerating from stop
- Rough or harsh shifting between gears
- Slipping sensation under hard acceleration
- Burning smell from transmission
- Check engine light with transmission codes
- Clutch slip warnings on iDrive display
How to Fix
Replace DCT clutch pack when symptoms appear. BMW recommends replacing all clutches together. Change DCT fluid every 30,000 miles with BMW-approved fluid to extend clutch life. Avoid excessive launch control use (limit to special occasions). Transmission adaptation reset via BMW software may temporarily improve shift quality. Extended warranty highly recommended for DCT-equipped M4s. Labor-intensive repair requires transmission removal.
Sources for this issue (1)
The SMG (Sequential Manual Gearbox) III hydraulic system in E63 M6 (2006-2010) and SMG-equipped E63/E64 645Ci/650i (2004-2010) suffers from hydraulic pump motor failure. 90% of SMG pump failures are caused by the pump MOTOR (carbon brush dust contamination), NOT the pump itself - but shops commonly misdiagnose and replace the entire pump assembly at $5,000-6,500 OEM cost. The pump motor brushes wear down over time, creating carbon dust that contaminates the motor internals. Motor-only replacement ($200-350) has a 90% success rate and does NOT require hydraulic bleeding. Full pump replacement requires hydraulic system bleeding and is significantly more expensive. MLREng/BimmerWorld offer upgraded pump assemblies ($449) for cases where motor-only replacement is insufficient.
Common Symptoms
- SMG warning light on dashboard
- Slow or delayed gear shifts
- SMG pump running continuously or excessively
- Transmission stuck in gear or neutral
- Grinding during shifts
- Complete loss of gear selection
How to Fix
Try pump motor-only replacement FIRST ($200-350 from SMG Society) - 90% success rate and no hydraulic bleed needed. If motor replacement fails, install MLREng/BimmerWorld upgraded pump ($449). OEM full pump replacement 23427571297 costs $5,000-6,500 and should be LAST resort. Total cost: $500-7,700 depending on approach. CRITICAL: 90% of failures are the pump motor, not the full pump - do not let shops misdiagnose and charge $5,000+ when a $350 motor fixes the issue.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Magneti Marelli 6-speed SMG pump motor A-SMG-006OEM23427571297; 23427507107Cross-refA-SMG-006
Confirmed failed 6-speed SMG electric pump-motor replacement. Confirm transmission ID and diagnosis..
- E63/E64 M6 SMG III pump motor A-SMG-030OEM23017841032Cross-refA-SMG-030
Confirmed failed M6 SMG III electric pump-motor replacement. Confirm hydraulic-pressure diagnosis before ordering..
As an Amazon Associate, we earn from qualifying purchases; other part links may also earn au7o a commission. Confirm fitment by VIN before buying.
Sources for this issue (1)
P0734 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0734 mean on a BMW?
P0734 stands for "Gear 4 Incorrect Ratio." This code means the Transmission/Powertrain Control Module detected an incorrect gear ratio in 4th gear. The module continuously compares input shaft speed to output shaft speed; if the ratio in 4th gear doesn't match the expected value, it sets P0734. This usually indicates the transmission is slipping or not fully engaging 4th gear due to a hydraulic, friction, or solenoid problem. Symptoms include slipping, flaring RPM, harsh or missed shifts, and possibly limp mode. On BMW it is documented across 4 models: M2, X1, M4, 6 Series.
What are the most common causes of P0734?
The most common causes of P0734 are: Low or degraded/burnt transmission fluid, Slipping clutch packs or worn friction elements in 4th gear, Stuck or faulty shift solenoid, Valve body / internal hydraulic leak or restriction, Worn or failing torque converter, Faulty input or output speed sensor, Internal mechanical wear (bands, planetary gears). The specific cause varies by vehicle.
How much does it cost to fix P0734 on a BMW?
Published repair estimates on BMW range from $500 to $8,000 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
Looking for P0734 on a different make?
View P0734 across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.