P077B: Output speed can have the right magnitude and the wrong direction

P077B checks the direction reported by the transmission output-speed sensor against direction calculated from hybrid motor-speed information. Its distinguishing feature is direction: two readings can have similar speed magnitude yet disagree about the direction of rotation.

The comparison needs trustworthy references

The source requires valid output-sensor hardware information and a valid motor-based output-speed estimate. Communication loss must be absent, and the P215C correlation fault must not be active. The output-speed and motor-speed estimates must also differ by no more than 50rpm, with estimated output speed at least 50rpm.

Under those conditions a direction mismatch lasting 0.35 seconds is the documented failure. This prevents a speed-magnitude discrepancy from being treated automatically as the direction error defined here.

Preserve signed data

A useful scan capture retains the direction or sign of the raw output-speed and motor-based values. Taking absolute values or recording only an unsigned speed can remove the evidence this monitor uses. Include validity and communication status so an unavailable reference is not mistaken for an opposite direction.

The pass criterion is the opposite relationship sustained for five seconds. The table does not identify a reversed connector, a specific sensor replacement or a safe dynamic test maneuver. Diagnosis and any movement-dependent testing require the correct hybrid-transmission service procedure and controlled professional conditions.

Source and applicability

GM 2010 10OBDG10 Hybrid Diagnostics, only the cited controller and monitor. These are historical calibration examples; individual vehicle, engine and hardware applicability is not established. GM PDF, page 210.