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DTC U1304: Lost Communication With UART System: Notes

WARNING: This page does not describe the selected car, but rather 7 other vehicles, including the 1999 Pontiac Grand Prix, 1999 Pontiac Firebird, 1999 Oldsmobile Intrigue, 1999 Chevrolet Camaro, and 1998 Pontiac Grand Prix. However, it is still accessible from the selected car via links, so may be relevant.
  1. Perform diagnostic system check. See DIAGNOSTIC SYSTEM CHECK. After performing diagnostic system check, go to next step.
  2. Turn ignition off. Disconnect EBCM/EBTCM connector C1. Connect pinout box to connector. Measure resistance between pinout box terminals No. 24 and 15. If resistance is infinite, go to step 4)  . If resistance is not infinite, go to next step.
  3. Repair short to ground in circuit No. 800 (Tan wire) between DLC and EBCM/EBTCM.
  4. Turn ignition switch to RUN position. Measure voltage between pinout box terminal No. 24. If battery voltage is present, go to next step. If battery voltage is not present, go to step 6)  .
  5. Repair short to battery voltage in circuit No. 800 (Tan wire) between DLC and EBCM/EBTCM.
  6. Disconnect PCM connector C4 for V8 engines and C1 for V6 engines. Using DVOM, measure resistance between pinout box terminal No. 24 and 15 (Tan wire) for V6 engines or 30 (Tan wire) for V8 engines of PCM connector. See WIRING DIAGRAM. If resistance is 0-2 ohms, go to step 8)  . If resistance is not 0-2 ohms, go to next step.
  7. Repair open or high resistance in circuit No. 800 (Tan wire) between DLC and EBCM/EBTCM.
  8. Replace PCM. Perform PCM relearn procedures.
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