Theory Of Operation

WARNING: This page is about a different variant/trim than selected.

The Transmission Control Module (TCM) can detect rationality failures of the Input (Turbine) Speed Sensor and Output Speed Sensor signals as well as the wheel speed and engine speed signals received through the Controller Area Network (CAN).

The TCM performs three diagnostic checks that include:

Multi sensor comparisons of up to three speed signals (input, output and wheel speed).
Monitoring of the gradient of the input speed signal.
Double failure monitoring to determine unique failure situations which could require unique limp-in functionality.

NOTE:

The transmission needs to be placed into Neutral to perform a 4L to 4H transfer case shift. If the operator is performing a 4L to 4H shift the potential exists for them to shift the transmission from Neutral to Drive and accelerate before the transfer case has actually shifted into 4H. The TCM deems the transfer case is in 4H since the operator did select 4H, but the transfer case had to stay in 4L because the operator shifted to Drive too early. The TCM will set P0721-00 because of the difference of the output shaft speed compared to the expected wheel speed in this scenario.