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P2851

Shift Fork Position Sensor A/B Correlation

The position signals of shift fork sensors A and B do not correlate as expected for the active gear pre-selection. Plausibility check fails.

  • Check engine light: Yes
  • Emissions related: No
  • Repair difficulty: medium

Symptoms

  • Check engine or transmission warning light on
  • Harsh, delayed, or missing shifts
  • Possible limp mode (locked in one gear)
  • Slipping or shuddering during gear changes

Common causes

Ordered by how often each turns out to be the cause.

  • Offset between the two sensors after replacementCommon
  • Sensor harness incorrectly swappedPossible

Parts involved

  • Shift Fork Position Sensor A
  • Shift Fork Position Sensor B
  • TCM

P2851 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.