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Home >> GMC >> 1991 >> Value Van 7.4 N >> Repair and Diagnosis >> Transmission >> Automatic Trans >> Diagnosis - A/T >> Diagnostic Flow Charts (Cars) >> Code 27 Or 28, Gear Switch Circuits - 3.3L With 3T40 Transaxle >> Diagnostic Aids

Diagnostic Aids

Check for poor connections at ECM pins. Inspect harness for incorrect routing (too close to high voltage wiring) or chafing. Monitor the voltage of each terminal while moving related harness connectors. If the failure is induced, the voltage reading will change.

Fig 1: Code 27 Or 28 Troubleshooting Flowchart (3.3L A & N Body)
G91B07318Courtesy of GENERAL MOTORS CORP.
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