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Rear Blower Motor Inoperative

NOTE: After making any repairs, perform BODY VERIFICATION TEST  under VERIFICATION TESTS.
  1. With the DRBIII® in FCM, read the active DTCs. If there are any active FCM DTCs present, see DIAGNOSTIC TROUBLE CODE IDENTIFICATION  table in the related category. With the DRBIII®, reset the ATC after repair/replacement is complete. If there are not any active FCM DTCs present, go to the next step.
  2. Turn the ignition off. Remove and inspect Intelligent Power Module (IPM) Fuse No. 12. If the fuse is open, go to the next step. If the fuse is not open, go to step  6.
  3. Replace IPM Fuse No. 12. Turn the ignition on. Operate the blower motor in all speeds. Start the engine and operate the ATC system in all modes and speeds. If the blower motor operates properly without blowing the fuse, refer to the wiring diagrams to help isolate a possible intermittent short to ground condition. See WIRING DIAGRAMS . With the DRBIII®, reset the ATC after repair/replacement is complete. If the blower motor does not operate properly without blowing the fuse, go to the next step.
  4. Turn the ignition off. Disconnect the Rear Blower Motor Power Module C1 harness connector. See Fig 1. Measure the resistance between ground and the Fused Rear Blower Relay Output circuit. If the resistance is below 10 k/ohms, repair the Fused Rear Blower Relay Output circuit for a short to ground. Replace IPM Fuse No. 12. With the DRBIII®, reset the ATC after repair/replacement is complete. If the resistance is above 10 k/ohms, go to the next step.
  5. Turn the ignition off. Replace IPM Fuse No. 12. Disconnect the Rear Blower Motor Power Module C1 harness connector. See Fig 1. Disconnect the Rear Blower Motor Power Module C2 harness connector. See Fig 1. Connect a jumper wire between the Fused Rear Blower Relay Output circuit in the Rear Blower Motor Power Module C1 harness connector and the Power Feed circuit in the Rear Blower Motor Power Module C2 harness connector. Connect a jumper wire between the Ground circuit in the Rear Blower Motor Power Module C1 harness connector and the Ground circuit in the Rear Blower Motor Power Module C2 harness connector. Turn the ignition on. If the Blower Motor operates at full speed without blowing the fuse, replace the Rear Blower Motor Power Module. See appropriate AUTOMATIC A/C-HEATER SYSTEMS article in HVAC. Replace IPM Fuse No. 12. With the DRBIII®, reset the ATC after repair/replacement is complete. If the Blower Motor does not operate at full speed without blowing the fuse, replace the Blower Motor. See appropriate AUTOMATIC A/C-HEATER SYSTEMS article in HVAC. Replace IPM Fuse No. 12. With the DRBIII®, reset the ATC after repair/replacement is complete.
    6. NOTE: The test light must illuminate brightly. Compare the brightness to that of a direct connection to the battery.
  6. Ensure IPM Fuse No. 12 is installed. Disconnect the Rear Blower Motor Power Module C1 harness connector. See Fig 1. Turn the ignition on. Using a 12-volt test light connected to ground, back probe the Fused Rear Blower Relay Output circuit in the Rear Blower Motor Power Module C1 harness connector. If the test light illuminates brightly, go to the next step. If the test light does not illuminate brightly, go to  13.
  7. Turn the ignition off. Disconnect the Rear Blower Motor Power Module C1 harness connector. See Fig 1. Measure the resistance between ground and the Ground circuit. If the resistance is below 5 ohms, go to the next step. If the resistance is above 5 ohms, repair the Ground circuit for an open. With the DRBIII®, reset the ATC after repair/replacement is complete.
  8. Turn the ignition off. Disconnect the Rear Blower Motor Power Module C1 harness connector. See Fig 1. Disconnect the Automatic Temperature Control Module C2 harness connector. See Figure. Turn the ignition on. Measure the voltage of the Rear Blower Motor Control circuit. If there is any voltage present, repair the Rear Blower Motor Control circuit for a short to voltage. With the DRBIII®, reset the ATC after repair/replacement is complete. If there is not any voltage present, go to the next step.
  9. Turn the ignition off. Disconnect the Rear Blower Motor Power Module C1 harness connector. See Fig 1. Disconnect the Automatic Temperature Control Module C2 harness connector. See Figure. Measure the resistance of the Rear Blower Motor Control circuit between the Rear Blower Motor Power Module C1 harness connector and the Automatic Temperature Control Module C2 harness connector. If the resistance is below 5 ohms, go to the next step. If the resistance is above 5 ohms, repair the Rear Blower Motor Control circuit for an open. With the DRBIII®, reset the ATC after repair/replacement is complete.
  10. Turn the ignition off. Make sure that the Rear Blower Motor Power Module C1 harness connector is connected to the Rear Blower Motor Power Module. Make sure that the Automatic Temperature Control Module C2 harness connector is connected to the Automatic Temperature Control Module. Start the engine. Press the ATC Power switch on. Set the Rear System switch on the ATC module to the Rear Control position. Set the blower switch on the Rear ATC Control panel to LO speed. While back probing, measure the voltage of the Rear Blower Motor Control circuit in the Automatic Temperature Control Module C2 harness connector. If the voltage is above 10 volts, go to the next step. If the voltage is below 10 volts, replace the Rear Blower Motor Power Module. With the DRBIII®, reset the ATC after repair/replacement is complete.
    11. NOTE: The Rear Blower Motor Power Module provides a 10 volt signal to the ATC Module over the Rear Blower Motor Control circuit. The ATC Module provides a variable duty cycle ground to the 10 volt signal based on input from the Rear Blower switch.
    NOTE: When the Rear Blower switch is set to LO speed, the ATC Module provides a short duty cycle (less time grounding the signal voltage).
    NOTE: As higher blower speeds are requested, the ATC Module increases the duty cycle (more time grounding the signal voltage).
    NOTE: When the Rear Blower switch reaches HI speed, the duty cycle increases to where the signal pattern is almost a flat line (with brief voltage spikes).
  11. Turn the ignition off. Reconnect all previously disconnected components. Connect the DRBIII® X10 Scope Probe (CH7061) to Channel 1 on the DRBIII®. Select the following from the DRBIII® menu: PEP Module Tools; Lab Scope; Live Data; and Lab Scope. Press F2 and then press Enter. Using the left/right arrow keys, set the time to 10ms/Div. Press F2. Using the up/down arrow keys, set the voltage range to +20v. Press Enter to move the cursor to Probe. Using the up/down arrow keys, set the Probe to X10. Press F2. Start the engine. Press the ATC Power switch on. Set the Rear System switch on the ATC module to the Rear Control position. Using the X10 Scope Probe, back probe the Rear Blower Motor Control circuit in the Automatic Temperature Control Module C2 harness connector. Set the blower switch on the Rear ATC Control panel to LO speed then slowly move it to HI speed while observing the DRBIII® display. The voltage on the scope pattern should cycle from approximately 2 volts (duty cycle on) to 10 volts (duty cycle off) for all blower speeds. The duty cycle pattern should change smoothly as the Rear Blower switch is turned from LO to HI. The duty cycle on time should change from approximately 8 ms at LO speed, to 15 ms at medium speed, and to 25 ms at HI speed. If the DRBIII displays the voltage range and duty cycle as described above, go to the next step. If the DRBIII does not display the voltage range and duty cycle as described above, replace the Automatic Temperature Control Module. See A/C-HEATER CONTROL PANEL  under REMOVAL & INSTALLATION. With the DRBIII®, reset the ATC after repair/replacement is complete.
  12. Turn the ignition off. Disconnect the Rear Blower Motor Power Module C1 harness connector. See Fig 1. Disconnect the Rear Blower Motor Power Module C2 harness connector. Connect a jumper wire between the Fused Rear Blower Relay Output circuit in the Rear Blower Motor Power Module C1 harness connector and the Power Feed circuit in the Rear Blower Motor Power Module C2 harness connector. Connect a jumper wire between the Ground circuit in the Rear Blower Motor Power Module C1 harness connector and the Ground circuit in the Rear Blower Motor Power Module C2 harness connector. Turn the ignition on. If the Blower Motor operates at full speed, replace the Rear Blower Motor Power Module. See appropriate AUTOMATIC A/C-HEATER SYSTEMS article in HVAC. With the DRBIII®, reset the ATC after repair/replacement is complete. If the Blower Motor does not operate at full speed, replace the Blower Motor. See appropriate AUTOMATIC A/C-HEATER SYSTEMS article in HVAC. With the DRBIII®, reset the ATC after repair/replacement is complete.
    13. NOTE: The test light must illuminate brightly. Compare the brightness to that of a direct connection to the battery.
  13. Turn the ignition off. Remove the Rear Blower Motor Relay from the IPM. Using a 12-volt test light connected to ground, probe cavity 30 of the Rear Blower Motor Relay connector. If the test light illuminates brightly, go to the next step. If the test light does not illuminate brightly, replace the IPM. With the DRBIII®, reset the ATC after repair/replacement is complete.
  14. Turn the ignition off. Remove the Rear Blower Motor Relay from the IPM. Remove IPM Fuse No. 12. Measure the resistance between cavity 87 of the Rear Blower Motor Relay connector and IPM Fuse No. 12 (power input cavity). If the resistance is below 5 ohms, go to the next step. If the resistance is above 5 ohms, replace the IPM. With the DRBIII®, reset the ATC after repair/replacement is complete.
    15. NOTE: The test light must illuminate brightly. Compare the brightness to that of a direct connection to the battery.
  15. Turn the ignition off. Make sure that the Rear Blower Motor Relay is installed. Remove IPM Fuse No. 12. Turn the ignition on. Using a 12-volt test light connected to ground, probe IPM Fuse No. 12 (power input cavity). If the test light illuminates brightly, go to the next step. If the test light does not illuminate brightly, replace the Rear Blower Motor Relay. With the DRBIII®, reset the ATC after repair/replacement is complete.
  16. Turn the ignition off. Remove IPM Fuse No. 12. Disconnect the IPM C8 harness connector. See Figure. Measure the resistance between IPM Fuse No. 12 (power output cavity) and cavity No. 7 of the IPM C8 connector (IPM side). If the resistance is below 5 ohms, repair the Fused Rear Blower Motor Relay Output circuit for an open. With the DRBIII®, reset the ATC after repair/replacement is complete. If the resistance is above 5 ohms, replace the IPM. With the DRBIII®, reset the ATC after repair/replacement is complete.
Fig 1: Identifying Rear Blower Motor Power Module C1 & C2 Connectors
G00172182Courtesy of DAIMLERCHRYSLER CORP.
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