LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Cadillac >> 1999 >> Eldorado Base >> Repair and Diagnosis >> Body & Frame >> Body, Cab Control Systems >> Body Control Modules >> System Tests >> Scan Tool Will Not Communicate With Class 2 Serial Data
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Scan Tool Will Not Communicate With Class 2 Serial Data

  1. Perform DATA LINK COMMUNICATIONS DIAGNOSTIC SYSTEM CHECK  . Go to next step.
  2. Connect scan tool to another 1999 model year vehicle to ensure proper operation of scan tool. If scan tool operates on another vehicle, go to step  4 . If scan tool does not operate, go to next step.
  3. Refer to scan tool manufacture's instructions for proper operation. After repairing scan tool, go to DATA LINK COMMUNICATIONS DIAGNOSTIC SYSTEM CHECK  .
  4. Connect scan tool to malfunctioning vehicle. Check connections between DLC and scan tool connector. If connections are okay, go to step  6 . If connections are faulty, go to next step.
  5. Repair terminal contact between DLC and scan tool. After repairs, go to DATA LINK COMMUNICATIONS DIAGNOSTIC SYSTEM CHECK  .
  6. Turn ignition on. If scan tool powers up, go to step  12 . If scan tool does not power up, go to next step.
  7. Use DVOM to measure voltage between ground and DLC terminal No. 16 (Orange wire). See WIRING DIAGRAMS  . If reading is 10-15 volts, go to step  9 . If reading is not 10-15 volts, go to next step.
  8. Repair open or short to ground in Orange wire between fuse block and DLC. After repairs, go to DATA LINK COMMUNICATIONS DIAGNOSTIC SYSTEM CHECK  .
  9. Use DVOM to measure voltage between DLC terminals No. 16 (Orange wire) and No. 5 (Black/White wire). If reading is 10-15 volts, go to step  11 . If reading is not 10-15 volts, go to next step.
  10. Repair open in Black/White wire between ground and DLC. After repairs, go to DATA LINK COMMUNICATIONS DIAGNOSTIC SYSTEM CHECK  .
  11. Disconnect PCM connectors. Attempt to communicate with Body Control Module (PZM). If scan tool communicates, go to next step. If scan tool does not communicate, go to step  13 .
  12. Replace PCM. See REMOVAL, OVERHAUL & INSTALLATION - CARS article in ENGINE PERFORMANCE. After replacement, go to DATA LINK COMMUNICATIONS DIAGNOSTIC SYSTEM CHECK  .
  13. Disconnect EBTCM connectors. Attempt to communicate with PZM. If scan tool communicates, go to next step. If scan tool does not communicate, go to step  16 .
  14. Check for short to ground or short to battery voltage in Purple wire between EBTCM connector terminal No. 10 and PCM connector C1 terminal No. 58. If short was found, go to step  54 . If circuit is okay, go to next step.
  15. Replace EBTCM. See appropriate ANTI-LOCK BRAKES article in BRAKES. After replacement, go to DATA LINK COMMUNICATIONS DIAGNOSTIC SYSTEM CHECK  .
  16. Disconnect radio connector. Attempt to communicate with PZM. If scan tool communicates, go to next step. If scan tool does not communicate, go to step  18 .
  17. Replace radio. After replacement, go to DATA LINK COMMUNICATIONS DIAGNOSTIC SYSTEM CHECK  .
  18. Disconnect Instrument Panel Cluster (IPC) connector. Attempt to communicate with PZM. If scan tool communicates, go to next step. If scan tool does not communicate, go to step  20 .
  19. Replace IPC. See ANALOG & ELECTRONIC INSTRUMENT PANELS - DEVILLE & ELDORADO article. After replacement, go to DATA LINK COMMUNICATIONS DIAGNOSTIC SYSTEM CHECK  .
  20. If vehicle is equipped with D55 (front floor console), go to next step. If vehicle is not equipped with D55, go to step  24 .
  21. Disconnect A/C-heater control panel. Attempt to communicate with PZM. If scan tool communicates, go to next step. If scan tool does not communicate, go to step  24 .
  22. Check for short to ground or short to battery voltage in Purple wire between A/C-heater control panel connector terminal A8 and IPC connector C3 terminal D1. If short was found, go to step  54 . If circuit is okay, go to next step.
  23. Replace A/C-heater control panel. See appropriate AUTOMATIC A/C-HEATER SYSTEMS article in AIR CONDITIONING & HEATING. After replacement, go to DATA LINK COMMUNICATIONS DIAGNOSTIC SYSTEM CHECK  .
  24. If vehicle is equipped with A45 (Memory Personalization Package), go to next step. If vehicle is not equipped with A45, go to step  28 .
  25. Disconnect Memory Mirror Module (MMM) connector. Module is located under left side of instrument panel above brake pedal. Attempt to communicate with PZM. If scan tool communicates, go to next step. If scan tool does not communicate, go to step  28 .
  26. Check for short to ground or short to battery voltage in Purple wire between MMM connector C1 terminal E16 and IPC connector C3 terminal D1 (without D55) or A/C-heater control panel connector terminal A8 (with D55). If short was found, go to step  54 . If circuit is okay, go to next step.
  27. Replace MSM. After replacement, go to DATA LINK COMMUNICATIONS DIAGNOSTIC SYSTEM CHECK  .
  28. Disconnect A/C-heater programmer. Programmer is located behind the glove box. Attempt to communicate with PZM. If scan tool communicates, go to next step. If scan tool does not communicate, go to step  30 .
  29. Check for short to ground or short to battery voltage in Purple wire between A/C-heater programmer connector C2 terminal D2 and one of the following components:
    • MMM connector C1 terminals F16 (with A45).
    • A/C-heater control panel connector terminal B8 (with D55 and without A45).
    • IPC connector C3 terminal D1 (without A45 and D55).
    If short was found, go to step  54 . If circuit is okay, go to step  55 .
  30. If vehicle is equipped with factory cellular telephone, go to next step. If vehicle is equipped with aftermarket cellular telephone or has no telephone at all, go to step  33 .
  31. Disconnect cellular telephone module connector. Module is located in center console. Attempt to communicate with PZM. If scan tool communicates, go to next step. If scan tool does not communicate, go to step  33 .
  32. Replace cellular telephone module. After replacement, go to DATA LINK COMMUNICATIONS DIAGNOSTIC SYSTEM CHECK  .
  33. If vehicle is equipped with A45 (Memory Personalization Package), go to next step. If vehicle is not equipped with A45, go to step  36 .
  34. Disconnect Memory Seat Module (MSM) connector. Module is located under driver's seat. Attempt to communicate with PZM. If scan tool communicates, go to next step. If scan tool does not communicate, go to step  36 .
  35. Check for short to ground or short to battery voltage in Purple wire between MSM connector C1 terminal No. 26 and radio connector terminal E6. If short was found, go to step  54 . If circuit is okay, go to step  56 .
  36. Disconnect Sensing and Diagnostic Module (SDM) connector. Module is located under passenger's seat. Attempt to communicate with PZM. If scan tool communicates, go to next step. If scan tool does not communicate, go to step  39 .
  37. Check for short to ground or short to battery voltage in Purple wire between SDM connector terminal No. 17 and one or more of the following components:
    • MSM connector C1 terminal No. 25 (without A45).
    • Radio connector terminal E6 (with A45).
    If short was found, go to step  54 . If circuit is okay, go to next step.
  38. Replace SDM. See AIR BAG SERVICE & REPAIR MANUAL. After replacement, go to DATA LINK COMMUNICATIONS DIAGNOSTIC SYSTEM CHECK  .
  39. If vehicle is equipped with F45 (Real Time Dampening), go to next step. If vehicle is not equipped with F45, go to step  42 .
  40. Disconnect Continuous Variable Road Sensing Suspension (CVRSS) module connector. Module is located behind rear seat back on right side. Attempt to communicate with PZM. If scan tool communicates, go to next step. If scan tool does not communicate, go to step  42 .
  41. Replace CVRSS module. After replacement, go to DATA LINK COMMUNICATIONS DIAGNOSTIC SYSTEM CHECK  .
  42. If vehicle is equipped with UQ4 (4-speaker Bose system) or UQ6 (11-speaker Bose system with amplifier), go to next step. If vehicle is not equipped with UQ4 or UQ6, go to step  47 .
  43. Disconnect radio amplifier (DeVille) or the Radio Interface Module (RIM - Eldorado). Both the amplifier and the module are located behind the rear seat back in the center. Attempt to communicate with PZM. If scan tool communicates, go to next step. If scan tool does not communicate, go to step  47 .
  44. If vehicle is equipped with F45 (Real Time Dampening), go to next step. If vehicle is not equipped with F45, go to step  47 .
  45. Check for short to ground or short to battery voltage in Purple wire between CVRSS module connector C1 terminal D5 and one or more of the following components:
    • Radio amplifier connector C1 terminal B2 (DeVille).
    • RIM connector C1 terminal B2 (Eldorado).
    If short was found, go to step  54 . If circuit is okay, go to next step.
  46. Replace radio amplifier (DeVille) or replace the RIM (Eldorado). After replacement, go to DATA LINK COMMUNICATIONS DIAGNOSTIC SYSTEM CHECK  .
  47. Disconnect the Remote Function Actuator (RFA). RFA is located behind center of rear seat back. Attempt to communicate with PZM. If scan tool communicates, go to next step. If scan tool does not communicate, go to step  51 .
  48. If vehicle is equipped with F45, UQ4 or UQ6, go to next step. If vehicle is not equipped with F45, UQ4 or UQ6, go to step  50 .
  49. Check for short to ground or short to battery voltage in Purple wire between RFA module connector terminal No. 2 and one or more of the following components:
    • CVRSS module connector C1 terminal D5 (with F45 and without UQ4 or UQ6).
    • Radio amplifier connector C1 terminal B3 (DeVille).
    • RIM connector C1 terminal B3 (Eldorado).
    If short was found, go to step  54 . If circuit is okay, go to next step.
  50. Replace RFA module. After replacement, go to DATA LINK COMMUNICATIONS DIAGNOSTIC SYSTEM CHECK  .
  51. Reconnect IPC connector. Disconnect PZM connector. Attempt to communicate with IPC. If scan tool communicates, go to next step. If scan tool does not communicate, go to step  54 .
  52. Check for short to ground or short to battery voltage in Purple wire between PZM connector C1 terminal A2 and RFA module connector terminal No. 3. If short was found, go to step  54 . If circuit is okay, go to next step.
  53. Replace PZM. See PLATFORM ZONE MODULE (PZM)  . After replacement, go to DATA LINK COMMUNICATIONS DIAGNOSTIC SYSTEM CHECK  .
  54. Repair open, short to ground or short to battery voltage in Purple wire. After repairs, go to DATA LINK COMMUNICATIONS DIAGNOSTIC SYSTEM CHECK  .
  55. Replace A/C-heater control panel. See appropriate AUTOMATIC A/C-HEATER SYSTEMS article in AIR CONDITIONING & HEATING. After replacement, go to DATA LINK COMMUNICATIONS DIAGNOSTIC SYSTEM CHECK  .
  56. Replace MSM. See appropriate POWER SEATS article. After replacement, go to DATA LINK COMMUNICATIONS DIAGNOSTIC SYSTEM CHECK  .
scientia non olet · About LEMON Manuals