Maintenance Case: Why open a BMW transmIssion over 40,000 kilometers on the bad?

[vehicle information] a 2012 BMW 523Li sedan, the Car traveling 45,216 kilometers, equipped with 2.5L naturally aspirated engine while matching the company’s German ZF 8HP45 8-speed model Is electronically controlled Automatic transmIssion (8AT).


At first when shifting the transmIssion when there Is slippage signs and lockfiles case, can not travel directly afterwards. And the meter with a transmIssion gearbox failure and fault information presentation lights.

[overhaul process]

after checking with the owners of the failed rescue vehicles towed Car repair shop, Field Master diagnostic be connected first fault detection, fault codes result in two transmIssion electric control system; 420341 are: the transmIssion during the shift 4- X> than monitoring. And 421,342: identifying a predetermined position in the neutral to unwanted force transmIssion.

In a subsequent transmIssion examination, found that the ATF field master special black color, and Is accompanied by an odor paste burning smell, may be determined so Field Master mechanical failure inside the transmIssion Some of the larger (experience to judge the gearbox friction plate has been burning), so do not do first fault code analysIs decIsion dIsintegration of inspection.

When the transmIssion oil pan removed to find its interior contains a lot of metal particles, indicating that the internal gear mechanical transmIssion member certainly damage. So we continue to dIsmantle down.

When the hydraulic pressure control unit electromechanical detached later found to have more memory metal particles in the gearbox housing, while the front end without dIsassembling the pump and when the end of the flange, by hand rotation of the input shaft when the output shaft or the flange, which transmIssion has virtually scratch hear the voice, and has catching phenomenon, indicating the most likely damage the mechanical components fall the particles stuck bulk rotating member.

Finally, the transmIssion confirmation Is a rearmost set of planet gears serious damage. While dIsmantling process Is found, the groups have different drive friction platesAblative case degrees.

[Fault AnalysIs]

After Careful damage to planetary gear mechanIsm Failure AnalysIs, found to be the last Top shelf of a planetary gear planetary gear after falling off the Card in the drive, it Is due to what causes damage to the planetary gear mechanIsm so serious it?

There are several possible reasons:

a: poor lubrication gears, gear wear by examining Analyzing bearing signs of wear and erosion;

bIs: transmitting torque during the torque moment due to mutations leading to the Carrying capacity of the planetary gear mechanIsm Is limited damage;

III: ATF oil quality deteriorates where the friction slip, the transmIssion temperature Is too high.

Further, in an analysIs of the two original fault code: 420341- 4-x in transmIssion power should be instantly interrupted or slipping Is recorded in the computer as a shift gear when the shift bit error ratio caused by transmIssion; while 421342- predetermined position: It may be damaged planet Card in the drive to the gearbox still be detected in the computer power transmIssion cause of the malfunction in neutral.


1, damage to planetary gear mechanIsm manufacturers do not provide a separate, advIse clients replace the entire planetary gear mechanIsm, and using a small repair kits.

2, washed torque converter, a hydraulic control unit for electromechanical cleaning.

3, damage to the planetary gear mechanIsm with a large number of fine particles can contaminate the cooling fluid circulation system, thus replacing the cooler, it Is the best solution. Test failures can be completely ruled out after loading.

[Fault summary]

just a Car traveling less than three years of serious damage to the gearbox, probably with users vehicle usage conditions and driving habits have a direct relationship, then there Is a hidden factory, otherwIse the linePlanetary gear mechanIsm generally Will not damage so severe.