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Home >> Cadillac >> 1995 >> Seville SLS >> Repair and Diagnosis >> Electrical >> Gauges >> Instrument Panel >> Component Testing >> IPC Tests >> IPC Dimming Problem

IPC Dimming Problem

  1. IPC monitors parking light input circuit (Brown wire) from headlight switch to determine when headlight/parking lights are on. When lights are on, headlight switch converts dimming control output to Pulse Width Modulation (PWM) signal.
  2. This PWM signal is distributed to interior lighting units (i.e., radio, IPC, console, etc.). IPC "sees" parking lights "on" input (II94) at IPC terminal D3. IPC then knows when to monitor dimming value (ID42) at IPC terminal C10 to control dimming of IPC and radio Vacuum Fluorescent (VF) displays.
  3. To test dimming, enter self-diagnostics and record all trouble codes. See ENTERING SELF-DIAGNOSTICS  under SELF-DIAGNOSTICS. If Code I022 is set, repair this code problem before proceeding. See TROUBLE CODES  under SELF-DIAGNOSTICS. Exit self-diagnostics. Turn headlights on. Rotate dimmer switch while noting operation of backlighting for radio, IPC buttons, PRNDL indicator, etc., and all VF Green displays.
  4. If any or all bulb type lights fail to illuminate or dim, or lights stay on continuously, go to step 13). If all bulb type backlighting lights do illuminate, go to next step.
  5. Notice VF Green lighting. If radio VF dims correctly but IPC remains bright, replace IPC. See INSTRUMENT PANEL CLUSTER  under REMOVAL & INSTALLATION. If radio VF and IPC are bright and do not change with dimmer, go to next step. If IPC dims, but radio does not, go to step 7). If radio dims but IPC is blank, go to step 11).
  6. Enter diagnostics and select input parameter II94. Turn headlights on. If II94 reads HI, replace IPC. See INSTRUMENT PANEL CLUSTER  under REMOVAL & INSTALLATION. If II94 reads LO, repair open in Brown wire circuit between IPC and splice S411. S411 is located to left of rear seat bottom section, enclosed in a flat plastic harness cover. S411 is located inside flat cover about 5 inches from bottom of cover.
  7. If IPC does dim, but radio does not and radio remains blank, replace radio control head. If radio remains full bright, enter self-diagnostics and select IPC OVERRIDE IS45 (VF Output). See ENTERING SELF-DIAGNOSTICS  under SELF-DIAGNOSTICS. Locate radio control head connector C2 (7-pin) terminal No. 3 (Purple/White wire). This operation may require removal of radio control head from dash if vehicle is console equipped.
  8. Using DVOM, backprobe radio control head connector C2 (7-pin) terminal No. 3 (Purple/White wire) while moving value of IS45 from 00 to 99. At "99" value, IPC should be at full bright and DVOM should read about zero volts. At "00" value, IPC should be at maximum dim (Black out) and DVOM should read about 5 volts.
  9. If voltage readings are as described, go to next step. If voltage readings are not as described, repair open or short in Purple/White wire between IPC and radio control head. If no open or short is found, replace IPC. See INSTRUMENT PANEL CLUSTER  under REMOVAL & INSTALLATION.
  10. Leave headlights on and measure voltage at radio control head connector C1 (9-pin) terminal No. 6 or 7. (Brown wire). If voltage is 10 volts or more, replace radio control head. If voltage is less than 10 volts, repair open in Brown wire between radio and connector C203. Connector C203 contains 23 terminals and is located to right of steering column, near rear of radio control head. Splice S409 is located in Brown wire between radio head terminal No. 6 or 7 and fuse D11.
  11. Disconnect radio control head connector C2 (7-pin). If IPC illuminates, replace radio control head. If IPC remains blank, use DVOM to measure voltage at radio control head harness connector C2 terminal No. 5 (Orange/Black wire).
  12. If voltage reading is 10 volts or more, replace IPC. See INSTRUMENT PANEL CLUSTER  under REMOVAL & INSTALLATION. If voltage reading is less than 10 volts, repair open or short to ground in Orange/Black wire circuit between IPC and radio control head. If wire is okay, replace IPC. See INSTRUMENT PANEL CLUSTER  under REMOVAL & INSTALLATION.
  13. If none of the bulb type backlighting lights are on, check fuse D13 and go to next step. If all bulb type backlighting lights stay on continuously, repair short to voltage in Gray wire circuit between IPC and headlight switch. If only some lights illuminate, repair open in Gray wire circuit or Black ground wire circuit, or replace bad bulbs. See WIRING DIAGRAMS.
  14. Check for voltage at trunk fuse block fuse D13 with headlights on. If fuse is blown, go to next step. If no voltage exists, repair open in power feed to fuse. If voltage exists, repair open between trunk fuse D13 and splice S411. Splice S411 is located left of rear seat bottom section, enclosed in flat plastic harness cover. S411 is located inside flat cover about 5 inches from bottom of cover.
  15. Turn headlights off. Disconnect 4-terminal connector at headlight switch. See HEADLIGHT/TWILIGHT SENTINEL SWITCH MODULE  under REMOVAL & INSTALLATION. Remove Gray wire terminal from 4-terminal connector cavity. Reconnect 4-terminal connector to headlight switch (without Gray wire). Replace fuse and turn headlights on. Rotate dimmer switch through complete travel.
  16. If bulb backlighting now operates, go to next step. If bulb backlighting is still inoperative, repair short to ground in Brown wire circuit between headlight switch and IPC. If no short exists, replace headlight switch and retest.
  17. Turn off headlights. Disconnect 4-terminal connector from headlight switch. Reinstall Gray wire to 4-terminal connector. Reconnect headlight switch connector. Turn headlights on. Rotate dimmer switch through complete travel.
  18. If bulb backlighting is still inoperative, repair short to ground in Gray wire circuit between headlight switch and IPC. If bulb backlighting now operates, problem is intermittent. Recheck Gray and Brown wiring circuits for intermittent short. If no problem is found, replace headlight switch. See HEADLIGHT/TWILIGHT SENTINEL SWITCH MODULE  under REMOVAL & INSTALLATION.
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