My 1997 automatic BMW z3 will not stay locked up in 4th gear going down the highway. The only time the transmission is locked up is under slight acceleration. After extended highway miles the check eng light illuminates indicating a torque lock up problem. Any ideas? Thanks Jim
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BMW has been using electronically controlled automatic transmissions in most models since the late 80s. These transmission systems employ a transmission control unit which controls electrical solenoids to manipulate the various control and shift valves and functions in the transmission valve body. When the transmission control unit detects a problem that it thinks could be damaging to the transmission or engine, it goes into a fail-safe or limp mode. In this mode, the transmission will function in reverse normally, but in forward it will operate in only one gear (whether you have the shifter in D, or any of the lower gears). This will typically be 3rd or 4th gear, depending on the model. It will start in this gear and stay in this gear with no shifting. You would experience this as sluggish acceleration and higher than normal engine speed at about 40 mph and above.
If you must drive the vehicle when the transmission is in the fail safe mode, accelerate gently and keep the road speed lower than full highway speed.
Earlier models do not employ fault codes and must be diagnosed manually. Late models do employ fault codes and a diagnostic/scan machine can be used to check and read the faults to assist in diagnostics. Note that this is not your common OBDII engine management fault code tool. This is what A BMW dealer or a properly equipped independent shop would have for full vehicle system diagnostics and coding operations.
The car is now quite old, and the yellow gear ("cog") light indicates that the hydraulic pressure in the transmission is incorrect. Check fluid level and, if the fluid is murky or off-color, have the transmission serviced and the filter replaced.
You have air in the clutch system. Check the fluid level in the reservoir . Check for oil leaks at the slave cylinder ( replace if there is oil ) Have the system bled . IF you have fluid and the air comes back then replace the clutch master cylinder as the air will be bypassing the piston cup from blockages in the ports.
P0734=A/T 4th gear incorrect ratio. This has nothing to do with the speed sensor. If the speed sensor was faulty, it would also set OTHER gear incorrect ratio codes. My experience tells me the 4th gear incorrect ration indicates the torque converter clutch (TCC) is slipping and nothing more. Unless there was a speed sensor DTC (Diagnostic Trouble Code), the sensor is not the issue (yet). The fact P0734 was set (trust the computer), the TCC is slipping (out of range). Question: Maintenance history may indicate the wrong transmission fluid may have been introduced. Hyundai's Transmission fluid is strictly SPIII... there is no substitute. The incorrect fluid will cause 4th gear slippage. Now, having said that, it doesn't mean the 4th gear (lock-up) clutch isn't worn out. Have a qualified/certified Hyundai Service Technician properly diagnose this issue.
the rachet and lock on the handbrake handle itself is faulty and either needs 'loooking' at or replacing. leave the car in gear in addition to the handbrake to make sure ur car doesnt do a runner while u are waiting for repairs.