P0972: Allison shift-solenoid 1 open-circuit discrimination

The generic P0972 title is shift-solenoid A range/performance. GM's Allison summary specifically assigns it to an open electrical circuit for shift solenoid 1. Confirm that implementation before treating the code as a hydraulic performance problem.

The controller distinguishes an open from a ground fault

A hardware fault first creates a pending condition. If it persists, the controller performs an intrusive test by opening its low-side driver. The subsequent result helps distinguish the open-circuit classification from a short-to-ground condition. This is an internal electronic test, not an instruction to disconnect or jumper the circuit manually.

The description continues onto the next PDF page. Engine cranking or running, powered components, battery voltage within the specified range and an enabled high-side driver qualify the decision. Related supply-driver faults can prevent a valid result.

Preserve the exact classification

P0973 and P0974 are separately assigned to low and high circuit conditions. Keeping those codes distinct matters because an initial hardware indication is refined by the controller's follow-up test.

The source does not identify a failed solenoid rather than wiring from P0972 alone. Use the matching Allison service procedure to investigate the open path. Verification should establish a completed electrical test with the required driver and supply conditions. Clearing memory or judging shift quality alone cannot show that the circuit has passed its own diagnostic discrimination.

Source and applicability

2009 General Motors diagnostic parameter file 09OBDG01 Allison TRANS Diagnostics.pdf. Section-specific modules and calibrations; no per-code model or engine applicability established. This explanation describes the documented monitor, not a universal repair procedure.

GM diagnostic parameters, PDF page 33 · GM diagnostic parameters, PDF page 34.