P2805: Independent range-sensor channels disagree after duty-cycle adjustment

P2805 checks consistency between two independently connected internal transmission range sensors in the reviewed GM strategy. Sensor A goes to the TCM, while sensor B goes to the ECM and is transmitted to the TCM over the serial data bus.

The comparison is not raw equality

The controller adjusts sensor B for its high- or low-time representation, then checks how far the combined duty-cycle relationship deviates from 100%. A deviation above 5.2 percentage points is the documented failure boundary. Simply demanding equal raw A and B percentages would misrepresent this encoding.

Failure must persist for more than one second within a sample interval above 1.5 seconds, with 25-millisecond updates. The monitor also checks signal stability, using changes below 1.001 percentage points and a stability interval exceeding one second.

Communication and individual faults affect availability

P0707, P0708 and U0100 must not be active, sensor B data must be available from the ECM, and that B input must not already be faulted. Battery voltage must exceed 9 V for more than one second; the continuation includes an accessory-power mode condition.

A missing message or independently invalid B signal therefore changes the diagnostic question. P2805 supplies evidence of disagreement when the comparison is eligible; it does not automatically identify sensor A as physically defective.

Verification should confirm valid communication, correct duty-cycle interpretation and consistent signals in the applicable stable window. The source lists Type A, one-trip behavior and no universal parts replacement.

Source and applicability

Confirm the vehicle, transmission variant and relevant module before applying this monitor description. GM diagnostic table, PDF page 1210. GM diagnostic table, PDF page 1211.