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Home >> GMC >> 1991 >> Forward Control 4.3 Z, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes - Gasoline >> Trouble Code Charts >> Code 24, Vehicle Speed Sensor (3.1L Engine) >> Diagnostic Aids

Diagnostic Aids

A faulty or misadjusted Park/Neutral switch may set a false Code 24. Use Scan tester and check for proper signal in Drive, while wiggling shifter. Scan tester MPH reading should closely match speedometer when vehicle is moving. If code is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section.

Fig 1: Code 24 Schematic (3.1L) Vehicle Speed Sensor
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Fig 2: Code 24 Flow Chart (3.1L) Vehicle Speed Sensor
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