On Board Diagnosis Logic

This diagnosis monitors actual gear position by checking the torque converter slip ratio calculated by TCM as follows:

Torque converter slip ratio = A x C/B

1. A: Output shaft revolution signal from revolution sensor
2. B: Engine speed signal from ECM
3. C: Gear ratio determined as gear position which TCM supposes

If the actual gear position is higher than the position (1st) supposed by TCM, the slip ratio will be more than normal. In case the ratio exceeds the specified value, TCM judges this diagnosis malfunction.

This malfunction will be caused when either shift solenoid valve A is stuck open or shift solenoid valve B is stuck open.

Gear positions supposed by TCM are as follows.

1. In case of gear position with no malfunctions: 1  , 2, 3 and 4 positions
2. In case of gear position with shift solenoid valve A stuck open: 2*  , 2, 3 and 3 positions
3. In case of gear position with shift solenoid valve B stuck open: 4*  , 3, 3 and 4 positions to each gear position above

*: P0731 is detected.

Diagnostic trouble code A/T 1ST GR FNCTN with CONSULT-II or P0731 without CONSULT-II is detected when A/T cannot be shifted to the 1st gear position even if electrical circuit is good.