P0989: Pressure switch E fails to report the exhausted state

In GM's group 03 transmission summary, P0989 is evaluated through pressure-switch behavior. The controller expects switch E to indicate an exhausted state after the CBR1/C456 hydraulic-pressure condition has fallen to the specified low level and a calibrated delay has elapsed.

Timing separates a transition from a failure

The published low-pressure condition is at or below 50 kPa. The controller then applies a table-based hydraulic delay before judging the switch. If the switch still does not indicate exhausted, it increments the failure counter. The listed limit is 18 failing counts.

That delay matters because a switch observed immediately during a hydraulic transition is not being judged on the same basis as the completed monitor. The code's low-circuit wording should not be reduced to a single guessed connector-voltage test.

Both hydraulic expectation and switch information matter

Temperature, ignition voltage and engine-speed windows qualify the test. Several temperature, solenoid and range-related faults inhibit it. A missing new P0989 while those conditions block monitoring does not prove the switch has recovered.

Use the exact transmission's service procedure to distinguish an incorrect switch report from an incorrect hydraulic state. The summary does not establish which component is at fault. Verification should show the expected state after the appropriate delay and a completed monitor, rather than only a cleared code or a momentarily plausible pressure-switch reading.

Source and applicability

2009 General Motors diagnostic parameter file 09OBDG03 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 41.