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Test 3A: Rear Defogger Switch Failure

WARNING: This page is about a different car, the 1999 Dodge Intrepid and 1999 Chrysler Concorde. However, it is still accessible from the selected car via links, so may be relevant.
NOTE: Before proceeding with this test, perform TEST 1B: IDENTIFYING A/C-HEATER DIAGNOSTIC TROUBLE CODES  . BCM will set a DTC 50 if the rear defogger switch is detected in the depressed position for at least 30 seconds.
  1. Turn mode door control selector switch to recirculation/bi-level (full left) position. Using scan tool, clear DTC. See CLEARING DIAGNOSTIC TROUBLE CODES  under SELF-DIAGNOSTICS. Using scan tool, select SENSORS and observe MODE SWITCH MUX voltage. If voltage is about 0.2 volt, go to next step. If voltage is not about 0.2 volt, go to step  4 .
  2. Turn ignition off. Disconnect A/C-heater control head White 12-pin (C1) connector. Turn ignition on. Using scan tool, select SENSORS and observe MODE SWITCH MUX voltage. If voltage does not increase to 5.0 volts, go to next step. If voltage increases to 5.0 volts, replace A/C-heater control head. Perform VERIFICATION TEST  .
  3. Locate Body Control Module (BCM), attached to junction block, at left end of instrument panel. Turn ignition off. Disconnect BCM Black 24-pin (C2) connector. Using a DVOM, measure resistance between ground and BCM 24-pin connector terminal No. 22 (Red/Tan wire). If resistance is 100.0 ohms or more, replace BCM. If resistance is less than 100.0 ohms, repair short to ground in Red/Tan wire. Perform VERIFICATION TEST  .
  4. Press and release rear defogger switch several times. If rear defogger button does not stick, go to next step. If rear defogger button sticks, replace A/C-heater control head. Perform VERIFICATION TEST  .
  5. Using scan tool, select SENSORS and observe MODE SWITCH MUX voltage with rear defogger switch released. If voltage is not about 4.3 volts, go to next step. If voltage is about 4.3 volts, replace A/C-heater control head. Perform VERIFICATION TEST  .
  6. Using scan tool, select SENSORS and observe MODE SWITCH MUX voltage with rear defogger switch depressed. If voltage is about 0.4 volt, A/C-heater control switch is operating properly. Recheck system and check for DTCs. If voltage is not about 0.4 volt, replace A/C-heater control head. Perform VERIFICATION TEST  .
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