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Home >> GMC >> 1994 >> Forward Control 7.4 N >> Repair and Diagnosis >> External Pages >> Different car >> Section 13 (Engine Controls - Tests W/Codes - Electronic Transmission) >> Trouble Code Charts >> Code 87, High Gear Ratio Error >> Notes
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Code 87, High Gear Ratio Error: Notes

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Control module calculates ratio based on the transmission input speed and output speed sensor readings. Control module compares known ratio to the calculated ratio.

  1. An out-of-calibration transmission range pressure switch could falsely indicate actual transmission range.
  2. This test verifies the proper ratio.
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