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Home >> Cadillac >> 1996 >> Seville SLS >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System - Tests W/Codes >> Diagnostic Trouble Codes >> DTC P1660 - Cooling Fan Control Circuits >> Diagnostic Procedures
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Diagnostic Procedures

  1. Perform On-Board Diagnostic (OBD) System Check. After performing OBD system check, go to next step.
  2. Turn ignition on. Turn A/C controls off. Using scan tool in MISC TESTS select OUTPUT TESTS, then select FAN RELAYS. Note QUAD DRIVER 1 display and command ALL RELAYS off. If scan tool display indicates OK, go to next step. If scan tool display does not indicate OK, go to step 8).
  3. In MISC TESTS, select OUTPUT TESTS, then select FAN RELAYS. Note QUAD DRIVER 1 display and ALL RELAYS on. If scan tool display indicates OK, go to next step. If scan tool display does not indicate OK, go to step 5).
  4. If cooling fan is inoperative or if a fault is suspected, diagnose cooling fan. See SYSTEM/COMPONENT TESTS article. If cooling fan operates, fault is not present.
  5. While noting QUAD DRIVER 1 display, command FAN RELAY 1 on. If scan tool display indicates OK, go to step 7). If scan tool display does not indicate OK, go to next step.
  6. Store fluid life index as indicated on scan tool. Turn ignition to LOCK position and wait 30 seconds, then disconnect PCM harness connector C2. Remove fan relay 1 (low speed). Using DVOM, check voltage between ground and cooling fan low speed control circuit at PCM harness connector terminal. If voltage reading is .5 volt or less, go to step 18). If voltage reading is greater than .5 volt, go to step 16).
  7. Store fluid life index as indicated on scan tool. Turn ignition to LOCK position and wait 30 seconds, then disconnect PCM harness connector C2. Remove fan relays 2 and 3. Using DVOM, check voltage between ground and cooling fan high speed control circuit at PCM harness connector terminal. If voltage reading is .5 volt or less, go to step 18). If voltage reading is greater than .5 volt, go to step 17).
  8. With ALL RELAYS still commanded off, observe operation of both cooling fans. If either fan is operating, go to next step. If neither fan is operating, go to step 10).
  9. Store fluid life index as indicated on scan tool. Turn ignition to LOCK position and wait 30 seconds, then disconnect PCM harness connector C2. Turn ignition on. Using DVOM, check voltage between ground and cooling fan low speed control circuit at PCM harness connector terminal. If voltage reading is less than 10 volts, go to step 15). If voltage reading is 10 volts or greater, go to step 14).
  10. Store fluid life index as indicated on scan tool. Turn ignition to LOCK position and wait 30 seconds, then disconnect PCM harness connector C2. Turn ignition on. Using DVOM, check voltage between ground and cooling fan high and low speed control circuits at PCM harness connector terminal. If voltage reading is 10 volts or greater, go to step 18). If voltage reading is less than 10 volts, go to next step.
  11. If voltage reading from step 9) is low for both terminals, go to step 13). If voltage reading from step 9) is low only in one of the terminals, go to next step.
  12. Repair open in circuit or replace fan relay for the circuit that measured low.
  13. Repair cause of no voltage to both circuits. Replace fuse if blown.
  14. Repair short to ground in cooling fan high speed control circuit.
  15. Repair short to ground in cooling fan low speed control circuit.
  16. Repair short to voltage in cooling fan low speed control circuit.
  17. Repair short to voltage in cooling fan high speed control circuit.
  18. Check terminal contact at PCM. Repair as necessary. If terminal contact is okay, go to next step.
  19. Replace PCM. Program replacement PCM using required equipment.
Fig 1: DTC P1660 Schematic
G96I01715
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