Multiplex Control System Troubleshooting
TroubleshootingSpecial Tool Required:
MPCS Service Connector 07WAZ-001010A
1. Check the No.9 (10 A) fuse in the under-hood fuse/relay box and the No.10 (7.5 A) fuse in the under-dash fuse/relay box.
Are the fuses OK?
YES - Go to step 2.
NO - Find and repair the cause of the blown fuse.
2. Remove the dashboard lower cover.
3. Turn the ignition switch ON (II).
If the driver's seat belt is unbuckled, the beeper will beep five times.
4. Check self-diagnosis function Mode 1 for a diagnostic trouble code (DTC) by connecting the special tool (A) to the multiplex control inspection connector (B). After about 5 seconds, the spotlight and ceiling light should come on for 2 seconds, go out, then blink 0.2 second. This means that you are in Mode 1 of the self-diagnosis function.
5. If there is a DTC, it will blink, pause, then repeat the DTC as long as the ignition switch is ON (II).
Is there a repeating DTC?
YES - Count the blinks, then go to step 8.
NO - See if the SCS circuit is working properly. Go to step 6.
6. Check for continuity between the inspection connector T1 and body ground.
Is there continuity?
YES - Go to step 9.
NO - Go to step 7.
7. Check for continuity between the connector J of under-dash fuse/relay box No.4 terminal and body ground.
Is there continuity?
YES - Faulty under-dash fuse/relay box. Replace and check for DTCs.
NO - Repair the open in the wire, and recheck for DTCs.
8. About 1 second after you go into self-diagnosis mode 1, the ceiling light will indicate the DTC, and repeat it every 3 seconds. If there is more than one DTC, the system will indicate them in ascending order, beginning from the DTC with the lowest numerical value. Troubleshoot the DTCs as indicated:
- DTC 1, 2, and 3 (ECM P0600) simultaneously: Check for a short to body ground in the YEL wire between multiplex control unit terminal E10 and TCM terminal A2, and in the WHT/GRN wire between multiplex control unit terminal KIO and gauge assembly terminal A2. If both wires are OK, substitute a known-good multiplex control unit, gauge assembly, and ECM one at a time, in that order, and recheck for the DTCs after each substitution.
- DTC 2 and 5 simultaneously: Check for an open in the YEL wire between multiplex control unit terminal E10 and TCM terminal A2. If the wire is OK, substitute a known-good multiplex control unit, gauge assembly, and TCM one at a time, in that order, and recheck for the DTCs after each substitution.
- DTC 1, and 6 simultaneously: Check for an open in the WHT/GRN wire between multiplex control unit terminal KI0 and gauge assembly terminal A2. If the wire is OK, substitute a known-good multiplex control unit, gauge assembly, and ECM one at a time, in that order, and recheck for the DTCs after each substitution.
- DTC 1 only (no other DTCs present): Substitute a known-good multiplex control unit, and a gauge assembly one at a time, in that order, and recheck for the DTCs after each substitution.
- DTC 2 only (no other DTCs present): Substitute a known-good multiplex control unit, and a ECM one at a time, in that order, and recheck for the DTCs after each substitution.
- DTC 3 only (no other DTCs present): Substitute a known-good multiplex control unit, and recheck for the DTC.
- DTC 5 only (no other DTCs present): Substitute a known-good gauge assembly, and recheck for the DTC.
- DTC 6 only (no other DTCs present): Reprogram the ECM if it does not have the latest software, or substitute a known-good ECM, then recheck. If the symptom/indication goes away with a known-good ECM, replace the original ECM.
9. From Mode 1, disconnect the special tool from the multiplex control inspection connector for about 10 seconds, then reconnect it. The ceiling light should come on for 2 seconds, then blink twice more at 0.2 second intervals. This means the system has gone from Mode 1 to Mode 2.
NOTE: To cancel mode 2, disconnect the SCS service connector from the multiplex control inspection connector for more than 10 seconds or turn the ignition switch OFF.
10. Look in the following table for the switches most closely related to the problem. While still in Mode 2, operate the switches. If the circuit is OK, the ceiling light should blink once. If the circuit is faulty, there will be no indication. In the table is a list of circuits that can be checked in Mode 2.
Does the ceiling light blink?
YES - Go to step 12.
NO - Go to step 11.
11. Check two or three other circuits listed.
Does the ceiling light blink for each circuit?
YES - The additional circuits are OK. Repair the short or open in the circuit that failed the test in step 10.
NO - Multiple failed circuits can mean that the control unit has failed without triggering a DTC. Test a few more circuits. If they also fail, test the multiplex control unit inputs. If all the input tests are OK, substitute a known-good control unit, gauge assembly, and ECM, one at a time, 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.
12. Shift to the sleep mode:
Turn the ignition switch OFF.
If the control unit receives no inputs from the inputs listed, it will go into sleep mode after about 20 seconds.
13. Confirm the sleep mode:
Check for voltage on the YEL and WHT/GRN wires. There should be battery voltage in the sleep mode. Check the parasitic draw at the battery while shifting into the sleep mode. Amperage should change from about 70 to 80 mA to less than 10 mA.
14. Shift to the wake up mode:
When the ignition switch is turned ON (II), the multiplex control unit, gauge assembly, and ECM wake up at the same time without "talking" to each other through the communication lines. When any switch in the multiplex system is turned on, it wakes up its related control unit which, in turn, wakes up the other units.
After confirming the sleep mode, look in the table for the switch most closely related to the problem. Operate that switch and see if its control unit wakes up.
NOTE: If any control unit is faulty and will not wake up, several parts of the system will malfunction at the same time.
In the 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 - Intermittent failure; the system is OK at this time.
NO - Test the multiplex control unit inputs.