Diagnostic Aids

Check instrument cluster function. Check for opens in flex (printed) circuit. Ensure all connections are tight.
Suspected intermittents or opens at connectors can be detected with diagnostic service probe which permits voltage to be measured on wires without unplugging connectors. Ensure all terminals make good connection.
When diagnosing intermittent problems, select MALF HISTORY from Tech 1 scan tester ABS menu. Supplemental data can be used to duplicate problem.

Fig 1: Code 87 - Schematic

Courtesy of GENERAL MOTORS CORP.

Fig 2: Code 87 - Diagnostic Flowchart

Courtesy of GENERAL MOTORS CORP.