Bus +/- Signals Open From Memory/Heated Seat Module (MHSM)
NOTE:
Vehicles equipped with heated and memory seat systems are equipped with MHSM. Vehicles with heated seats and no memory systems are equipped with Heated Seat Module (HSM). Vehicles with memory system and no heated seats are equipped with Memory Seat Module (MSM).
- Turn ignition on. Using scan tool, select BODY then BODY COMPUTER. If scan tool is able to ID or communicate with BCM, go to next step. If scan tool cannot ID or communicate with BCM, go to BUS +/- SIGNAL OPEN FROM BODY CONTROL MODULE .
- Turn ignition off. Disconnect Memory Seat Module (MSM) connector C2. See Fig 2. MSM is located under driver's seat. Using DVOM, measure voltage between MSM connector C2 terminal No. 1 (Red wire) and ground. If voltage is greater than 10 volts, go to next step. If voltage is less than 10 volts, repair open in Red wire between MSM and splice located near breakout for lumbar switch harness. See WIRING DIAGRAMS in appropriate POWER SEATS article. Perform MEMORY/HEATED SEATS VERIFICATION TEST under VERIFICATION TESTS.
- Using DVOM, measure voltage between MSM connector C2 terminal No. 10 (Red wire) and ground. If voltage is greater than 10 volts, go to next step. If voltage is less than 10 volts, repair open in Red wire between junction block and MSM. See WIRING DIAGRAMS in appropriate POWER SEATS article. Perform MEMORY/HEATED SEATS VERIFICATION TEST under VERIFICATION TESTS.
- Using DVOM, measure resistance between ground and MSM connector C2 terminal No. 3 (Black wire). If resistance is less than 5 ohms, go to next step. If resistance is greater than 5 ohms, repair open in Black wire between MSM and splice located near breakout for power seat harness. Perform MEMORY/HEATED SEATS VERIFICATION TEST under VERIFICATION TESTS.
- Using DVOM, measure resistance between ground and MSM connector C2 terminal No. 12 (Black wire). If resistance is less than 5 ohms, go to next step. If resistance is greater than 5 ohms, repair open in Black wire between MSM and ground. Perform MEMORY/HEATED SEATS VERIFICATION TEST under VERIFICATION TESTS.
- Disconnect MSM connector C1. See Fig 1. Using DVOM, measure resistance between ground and MSM connector C1 terminal No. 19 (Black/Orange wire). If resistance is less than 5 ohms, go to next step. If resistance is greater than 5 ohms, repair open in Black/Orange wire between MSM and ground. Perform MEMORY/HEATED SEATS VERIFICATION TEST under VERIFICATION TESTS.NOTE: Ensure PCI bus communication between other modules exists before proceeding. If PCI bus module communication does not exist between other modules, go to appropriate system test.
- Use Scope Input Cable (CH7058), Cable-To-Probe Adapter (CH7062) and Red and Black test probes. Connect scope input cable to channel one connector on scan tool. Attach Red and Black test probes and cable-to-probe adapter to scope input cable. Select scan tool STANDALONE function. Select LAB SCOPE. Select LIVE. Select 12 VOLT SQUARE WAVE. Press F2 for scope display. Press F2 and use down arrow to select voltage range to 20 volts. Press F2 after selecting 20 volts. Connect Black test probe lead to ground and Red test probe lead to MSM connector C1 terminal No. 20 (Yellow/Violet wire). Turn ignition on. Observe voltage readings on scan tool. If reading pulses from zero to approximately 7.5 volts, go to next step. If reading is steady at zero volts, repair PCI bus circuit (Yellow/Violet wire) between MSM and Driver's Door Module (DDM). See appropriate wiring diagram in DATA LINK CONNECTORS article in WIRING DIAGRAMS. Perform MEMORY/HEATED SEATS VERIFICATION TEST under VERIFICATION TESTS.
- Replace MHSM. See MEMORY HEATED SEAT MODULE, HEATED SEAT MODULE, MEMORY SEAT MODULE under REMOVAL & INSTALLATION. Perform MEMORY/HEATED SEATS VERIFICATION TEST under VERIFICATION TESTS.