P0666: The transmission control module temperature-sensor circuit

BMW's 4EF3/P0666 chart is stored in the GS transmission controller and identifies its internal temperature-sensor circuit. In this source it is not a direct engine-coolant temperature fault, despite the generic code description allowing several types of control module.

The occurrence counter is diagnostic evidence

BMW instructs the technician to read the error-frequency counter. A frequency greater than two leads to mechatronic replacement in the chart. When the fault is passive, the specified path is to clear the memory and conduct a monitored road test; repeated registration then leads to replacement.

That distinction makes it important to record whether the fault is active or passive and retain its original count before clearing it. A single historical entry and a repeatedly registered fault do not receive identical treatment in this service record.

Conditions and limits

The monitor is enabled with ignition on and a stated voltage range of 7–16 V. Memory entry is controlled by a time- or event-based filter counter, but the chart does not disclose a particular temperature threshold or delay. It cannot support claims that a specific gearbox temperature alone triggers P0666.

The source gives no status report for the listed gearshift warning configurations and does not describe a separate emergency program for this entry. Those fields should not be generalized into a driving-safety promise.

Verification requires the correct transmission identification and a monitored check of recurrence. Mechatronic replacement is a transmission-specific professional operation; the N52 engine breadcrumb alone does not identify the installed gearbox or supply its replacement procedure.

Source and applicability

BMW diagnostic chart, P0666. 2006 BMW 330i Sedan (E90), N52 3.0L; BMW GS transmission monitor chart reproduced by Operation CHARM; confirm actual installed transmission. These values describe that documented monitor; they are not universal specifications for every vehicle displaying this code.