Multiplex Control System Troubleshooting
TroubleshootingSpecial Tool Required
MPCS Service Connector 07WAZ-001010A
1. Check the No. 9 (10 A) driver's and the No. 13 (7.5 A) passenger's fuses.
Are the fuses OK?
YES - Go to step 2.
NO - Find and repair the cause of the blown fuse.
2. Connect the special tool to the multiplex control inspection connector (A).
3. Turn the ignition switch ON (II). If the driver's seat belt is unbuckled, the seat belt reminder will beep five times.
4. After about 5 seconds, the ignition key light should come on and the beeper should beep for 2 seconds, go off for 0.2 seconds, then blink and beep for 0.2 second. This means that you are in Mode 1 of the self-diagnosis function. Check self-diagnosis function Mode 1 for a diagnostic trouble code (DTC).
- If the system enters Mode 1, go to step 5.
- If the system does not enter Mode 1, see if the SCS circuit is working properly. Go to step 6.
5. About 1 second after you go into self-diagnosis Mode 1, the ignition key light and beeper indicate the DTC, and repeat it every 3 seconds. If there is a code, it will blink/beep, pause, then repeat the code as long as the ignition switch is ON (II). If there is more than one DTC, the system will indicate them in ascending order, beginning from the DTC with the lowest numerical value.
Does the ignition key light blink and the beeper beep?
YES - There is a DTC. Count the blinks/beeps to find your DTC in the table, then go to step 9 and check the communication lines.
NO - If the system goes into Mode 1 as described in step 4, and there is no repeating DTC. Go to step 13.
6. Remove the special tool from the MPCS inspection connector.
7. Check for continuity between the No. 3 terminal of the inspection connector and the A10 terminal in the driver's multiplex control unit.
Is there continuity?
YES - Go to step 8.
NO - Repair open in the wire or replace the driver's under-dash fuse/relay box, and recheck for DTC's.
8. Check for continuity between the No. 3 terminal of the inspection connector and body ground G401.
Is there continuity?
YES - If there is still no Mode 1 confirmation, replace the driver's multiplex control unit and try again. After replacing the driver's multiplex control unit, the system confirms Mode 1 and there are no codes, go to step 12.
NO - Repair open in the wire, and recheck for DTC's.
9. With the ignition switch OFF, check for continuity according to the table.
Is there continuity?
YES - Go to step 10.
NO - Check for an open in the wire.
10. Turn the ignition switch ON (II), and check for voltage between the communication line and ground.
Does the voltage match the table?
YES - Communication lines are OK. Go to step 11.
NO - Repair the line according to the following.
- If the voltage is too high:
- Check for a short to another wire with voltage.
- Check for poor contact in the connectors at each control unit connector to the wire.
- If the voltage is too low:
- Check for a short to ground or to another wire.
- Check for poor connections at each control unit connector to the wire.
- Faulty circuit in one of the multiplex control units connected to the wire.
- If any one or all the control units are completely inoperative, perform the multiplex control unit input test.
11. Shift to the sleep mode:
- Turn the ignition switch OFF, and remove the key.
- Remove the special tool from the SCS connector.
- Cancel the key-off operation timer in the power window system by opening and closing one of the doors.
- Make sure the exterior lights are off. If you do not operate any switches related to the multiplex control units within 1 minute after meeting the above conditions, the system function shifts to the sleep mode. (All of the switches must be turned OFF except door lock knob switches).
12. Confirm the sleep mode:
- Check for voltage to ground on the BRN wire and PNK wire. There should be battery voltage in the sleep mode.
- Check the parasitic draw at the battery while shifting to sleep mode. Amperage should change from about 70 to 80 mA to less than 15 mA.
- If the vehicle does not go into the sleep mode, carefully perform Mode 2 test (see step 14), and check for faulty input for example a key cylinder switch keeping the system awake.
13. Confirm the wake up mode:
- When any switch in the multiplex system is turned on, it wakes up its related control unit which, in turns wakes up, wakes up the other units. After 15 seconds, it will return to sleep mode again if the switch is returned to the original position.
- When the ignition switch is turned to ON (II), all of the multiplex control units wake up at the same time without "talking" to each other through the communication lines.
If the wake up mode is confirmed on the first switch tested, and there is no problem with any other switch operation, the system is working correctly. Go to step 14.
NOTE: If any control unit is faulty and will not wake up, several parts of the system will malfunction at the same time.
After confirming the sleep mode and there are several switch failures, look in the following tables for the switches most closely related to the problem you may be having. Operate that switch and see if its control units wake up. Also use Mode 2 step 14 to confirm switch inputs.
In each table, the control unit is followed by a list of the switches and input signals that can wake it up.
Is the wake-up function OK?
YES - Troubleshoot the individual system function that had a problem. Go to step 14.
NO - Do the control unit input test for any inoperative multiplex control unit. If the input test is OK, replace the control unit.
14. With the system in Mode 1 and the ignition switch still ON (II), disconnect the special tool from the multiplex control inspection connector for about 5 to 10 seconds, then reconnect it. The ignition key light should come on and the beeper should beep for 2 seconds, then blink and beep twice more at 0.2 second intervals. This means the system has gone from Mode 1 to Mode 2. Go to step 15.
NOTE: To cancel mode 2, disconnect the MPCS service connector from the multiplex control inspection connector for more than 10 seconds or turn the ignition switch OFF.
15. Look in the following tables for the switch most closely related to the problem. While still in Mode 2, operate that switch to test the switch, the circuit between the switch and its control unit. If the circuit is OK, the ignition key light should blink once and the beeper should beep once. If the circuit is faulty, there will be no indication. The blink/beep occurs only when the switch input is grounded (except audio, DVD, and navigation systems which blink/ beep when disconnected.)
Does the ignition key light blink and beeper beep?
YES - The circuit is OK. Refer to the test(s) for that individual system.
NO - Go to step 16.
In each table, the control unit is followed by a list of circuits that it can check in Mode 2.
A second key is necessary to test the key cylinder switches. If only one key is available, cut a second key from a non-immobilizer type key blank for the test.
NOTE: When testing the door lock knob switches, make sure all three passenger doors and tailgate are locked. After unlocking the door, being tested make sure to return the door lock knob switch to the lock position otherwise the test results will be inaccurate.
NOTE: The key cylinder switches should only beep/ flash when turned to lock or unlock. If they beep/flash when returning to the neutral position, the switch is defective. Adjust or replace the switch.
16. Check two or three more circuits listed for that control unit.
Does the ignition key light blink and the beeper beep for each circuit?
YES - The additional circuits are OK. Repair the short or open in the circuit that failed the test in the preceding step.
NO - Multiple failed circuits can mean that the control unit has failed, without triggering a DTC. Test a few more circuits. If they are all functions of the same multiplex control unit, first do the control unit input test, then substitute a known-good control unit, then recheck. If the system works properly, the original control unit is faulty; replace it. If there is still a malfunction, substitute a known-good control unit for the next most likely faulty control unit, then recheck. If the system works properly, that control unit is faulty; replace it.