3.8 Gear Monitoring

3.8 Gear Monitoring
3.8.1 Gear Ratio
The objective behind gear monitoring is to detect non-electrical errors that are caused by slipping clutches or by the mechanical failure of actuators. When outside shift functions, verification checks are conducted for the output speed in relation to the turbine speed. Failure results in a default gear being selected by the TCM.

When the TCM detects that both the output shaft speed and engine speed are above the thresholds required for the transmission to shift, it checks to confirm that the shift is in progress. If no shift is happening then the transmission fluid temperature is checked to ensure it is above its minimum threshold. If the fluid temperature is OK the level of slip is also checked. If the level of slip exceeds its threshold then a fault timer is started and the checks repeated. The level of slip threshold is variable defined by an internal map of permitted slip.

When the fault timer exceeds its predefined threshold, a fault counter is incremented. When the counter exceeds a defined limit, the relevant IDTC is logged.

3.8.2 Gear Load
These monitors identify excessive or reduced slip during gear changes. The excessive slip part of the monitors is caused by the engaging clutch not coming on quickly enough. The reduced slip monitoring identifies that the off-going clutch is not coming off quickly enough. These monitors run continuously as long as the entry conditions continue to be satisfied.

When a gearshift is detected the monitor initially checks that the transmission fluid temperature and output shaft speeds are both above their required thresholds for the monitor to run. If either is not above its threshold, then the monitor is stopped.

The level of slip is first checked against the slip high threshold. If the actual slip exceeds the high threshold then a fault present timer is incremented and the check repeated. When the fault present timer exceeds it predefined threshold then the shift is aborted and a fault counter is incremented.

If the level of slip is below the slip high threshold, it is then checked against the slip low threshold. If the actual slip is less than the low threshold then a fault present timer is incremented and the check repeated. When the fault present timer exceeds it predefined threshold then the shift is aborted and a fault counter is incremented.

When the fault counter exceeds its predefined threshold, the relevant IDTC is logged.
































If the above table does not include details of the following enabling conditions: - IAT, ECT, vehicle speed range, and time after engine start-up then the state of these parameters has no influence upon the execution of the monitor.