BMW transmission temperature is too high causes and fault repair program graphic sharing


Today our automatic transmission repair point shares a BMW 525Li transmission temperature overhaul case with the majority of car enthusiasts for your reference.

A car enthusiast asked us by phone, and it turned out that the owner's BMW 525Li display showed that the transmission temperature was too high.

BMW transmission temperature is too high fault analysis.

After the owner arrived at the store, our BMW transmission service technician picked up the car, communicated with the owner, and conducted a test drive, the car is a 2012 BMW 525Li. configured N20 engine, currently running 120,000 km. The customer feedback vehicle driving prompted the transmission oil temperature is too high, in the BMW 4S store replaced the transmission fluid kit, transmission valve body and transmission radiator still did not solve the problem. Test drive with the customer, in the driving does prompt the transmission high temperature tips, the fault does exist.

Connect the diagnostic instrument to read the transmission control unit fault code. There is a fault about the transmission oil temperature is too high, from the fault code analysis consider the following points.

(1) transmission oil level. It is known that too much transmission fluid can also lead to high transmission oil temperature.

(2) transmission oil cooling problems. Poor transmission oil heat dissipation will also lead to high oil temperature. Is dependent on coolant heat dissipation, engine oil pan on the left side of a radiator, the owner has replaced a new one. It means that the engine cooling is not between the problem, thermostat, water pump and cooling fan are working properly.


(3) the transmission valve body on the oil temperature sensor signal distortion.

After the object of suspicion next to verify one by one, from simple to complex first run the vehicle to the oil and water temperature to the standard temperature after unscrewing the transmission side of the oil hole bolts, found that the oil level is normal and transmission fluid oil bright no obvious dirt, can exclude the transmission oil level and oil problems. Next to investigate the problem of heat dissipation, radiator just replaced the temporary disregard, loosen to the radiator inlet and outlet pipes, found that the pipeline oil can flow evenly, with an air gun to blow into the oil pipe in the return side without dirt and airflow uniform and powerful, excluding the radiator pipeline blockage dirty situation, view the water tank condenser appearance clean, the middle sandwich permeable no foreign matter, excluding the problem of poor external heat dissipation. Next, with the help of diagnostic instrument to read different speed and water temperature, water temperature, oil temperature and transmission oil temperature of the actual value are normal.

Repeatedly test several times are normal, basically rule out the problem of heat dissipation and signal distortion. The fault is occasional, the data is normal and can only be used as a reference when the fault does not appear, only the value when the fault is reproduced is meaningful, and the customer communication with the diagnostic instrument road test, through repeated road tests found a detail, when the fault phenomenon occurs when the engine meter tachometer stuck in about 3500r/min and the central display reported a fault.


Only in the tachometer stuck around 3500r/min when the fault reappears and the diagnostic instrument shows the crankshaft signal missing fault.

There is a relationship between engine speed, crankshaft signal and transmission oil temperature. zf8hp transmission has the fault of high torque converter temperature, the torque converter has no actual oil temperature sensor, this temperature is calculated according to engine speed, transmission output speed and other parameters, that is, the torque converter pump wheel and turbine speed slip calculation. When the pump wheel speed and turbo speed slip is too large, the calculated temperature of the torque converter will be higher than 145℃, and the transmission will show the overheating alarm prompt. Replace the crankshaft position sensor and signal disk after repeated test drive fault no longer appear, so the fault is solved.