Diagnostic Aids

Code will set if PCM detects one of 2 illegal combinations. Check all connections for good contact.

Using a scan tester, monitor QDM status while moving related harness connectors, including ECM harness. If a failure is induced, a fault will appear on scan tester. If code reappears and no faults can be found, replace ECM.

Fig 1: Code 28 - Trans. Range Pressure Switch Flowchart (3.4L "F" Body, 4.3L & 5.7L)