Multiplex Control System: Overview Honda Pilot I

Scheme 1

Scheme 2

System Descriptions

The multiplex control system has four internal functions

1. Multiplexing (sends multiple signals over shared wires)
2. Wake up/sleep modes (runs at full power only on demand to reduce battery draw)
3. Fail-safe (fixes or ignores faulty signals)
4. Self-diagnosis (Mode 1 for the system, Mode 2 for input lines)

The system controls the function of the following circuits

1. Engine oil pressure indicator
2. Seat belt reminder ('03 model)
3. Lights-on reminder
4. Key-in reminder
5. Key light timer
6. Dash lights brightness control
7. Entry light control
8. Automatic lights-off
9. Power door locks
10. Power window (including key-off timer operation)
11. Windshield wiper/washer (including speed sensitive intermittent wiper)
12. Security alarm
13. Rear window intermittent wiper

Description

Mode 1 is a communication line and CPU self test. If a problem occurs on a communication wire or with an individual control unit the multiplex system will store a DTC as long as the fault is still present.

Scheme 3

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Scheme 5

Scheme 6

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Scheme 8

Scheme 9

Scheme 10

Scheme 11

1. Check the No. 9 (10A) fuse in the driver's under-dash fuse/relay box and the No. 13 (7.5A) fuse in the passenger's 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. 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). Did the multiplex system enter Mode 1? YES -Go to step 5. NO -Go to step 6 .
5. Check for a DTC. If there are no DTCs present: The ignition key light and beeper will not blink/beep again after the Mode 1 indication. If there is a DTC present: About 1 second after entering Mode 1, the ignition key light and beeper indicate the DTC(s), then repeat it every 3 seconds. If there is more than one DTC, the system will indicate them in succeeding order. Is there a DTC present? YES -Follow the procedure in the chart below. NO -Go to Mode 2.
6. Remove the special tool from the MPCS inspection connector.
7. Remove driver's multiplex control unit from the driver's under-dash fuse/relay box.
8. Check for voltage between the A24 terminal of the driver's under-dash fuse/relay box socket and body ground. Is there battery voltage? YES -Go to step 9. NO -Replace the driver's under-dash fuse/relay box.
9. Turn the ignition switch ON (II).
10. Check for voltage between A12 terminal of the driver's under-dash fuse/relay box socket and body ground. Is there battery voltage? YES -Go to step 11. NO -Repair an open in the wire between No. 13 (7.5A) fuse in the passenger's under-dash fuse/relay box and driver's under-dash fuse/relay box socket.
11. Check for continuity between A14 terminal of the driver's under-dash fuse/relay box socket and body ground. Is there continuity? YES -Go to step 12. NO -Repair an open in the wire between driver's multiplex control unit connector and body ground. If the wire is OK, check for poor ground at G401.
12. Check for continuity between the B11 terminal of the driver's multiplex control unit connector and body ground. Is there continuity? YES -Go to step 13. NO -Repair an open in the wire between the driver's multiplex control unit connector and body ground. If the wire is OK, check for poor ground at G501.
13. Check for continuity between the No. 3 terminal of the MPCS inspection connector and the A15 terminal of the driver's under-dash fuse/relay box socket. Is there continuity? YES -Go to step 14. NO -Faulty driver's under-dash fuse/relay box internal circuit between the inspection connector and the driver's under-dash fuse/relay box. Replace the driver's under-dash fuse/relay box.
14. Check for continuity between the No. 1 terminal of the multiplex control inspection connector and body ground. Is there continuity? YES -If there is still no mode 1 indication, replace the driver's multiplex control unit and recheck the symptom. NO -Repair an open in the wire between the inspection connector and body ground. If the wire is OK, check for a poor ground at G401.

Mode 2 is an easy way to identify a problem circuit with out having to test the circuit with a DVOM. Mode 2 will confirm a switch/circuit is working by flashing the ignition key light and sounding the beeper as the circuit is used. The multiplex control system will confirm inputs as they are grounded except for the following circuits

1. Turning the intermittent wiper ring (several confirmations as ring is turned).
2. Turning the dash light illumination dimmer (several confirmations as the knob is turned).
3. The Audio unit, Navigation display, RES display, DVD player (confirmation as any one component is disconnected).

Scheme 12

Scheme 13

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Scheme 15

1. From Mode 1, disconnect the special tool from the multiplex control (MPCS) inspection connector for between 5 and 10 seconds, then reconnect it. The ignition key light should come on and the beeper should beep for 2 seconds, then blink/beep twice more at 0.2 second intervals. This indicates the system has entered Mode 2. NOTE: To cancel Mode 2, disconnect the special tool from the multiplex control inspection connector for more than 10 seconds or turn the ignition switch OFF.
2. Operate the switches as described in the charts below. NOTE: 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. When testing the door lock knob switches, make sure all three passenger doors are locked. After unlocking the door, make sure to return the door lock knob switch to the lock position, otherwise the test results will be inaccurate. Did the multiplex control system confirm all the circuits by flashing the ignition key light and sounding the beeper? YES -The multiplex system is OK, if the symptom is still present, go to the input test for the system with the problem ( see list below), or refer to multiplex control unit input test (see «Multiplex Control Unit Input Test»(ref-174054-S29467265802005051900000) ). System Power door locks (see «CONTROL UNIT INPUT TEST»(ref-174056-S38052416732005052100000) ) Security (see «CONTROL UNIT INPUT TEST»(ref-174056-S38052416732005052100000) ) Keyless (see «CONTROL UNIT INPUT TEST»(ref-174056-S38052416732005052100000) ) Power windows (Includes key-off timer operation) (see page «CONTROL UNIT INPUT TEST»(ref-174055-S33305711042005042800000) ) Entry light control, Key light timer (see «CONTROL UNIT INPUT TEST»(ref-174045-S22559321242005051400000) ) Wiper controls (front and rear) (see «CONTROL UNIT INPUT TEST»(ref-174050-S30967186242005051400000) ) Automatic lights off (see «AUTO-OFF HEADLIGHTS CONTROL UNIT INPUT TEST»(/honda/pilot/i-2002-2005/remont/exterior-lights/#exterior-lights) ) Reminder chimes (Key-in, seat belt, lights-on) (see «CONTROL UNIT INPUT TEST»(ref-174043-S13956468242005050300000) ) Dash lights brightness control (see «CONTROL UNIT INPUT TEST»(ref-174045-S07344923252005051400000) ) Engine oil pressure indicator (see «CONTROL UNIT INPUT TEST»(ref-174043-S13956468242005050300000) ) NO -Find the open or short in the circuit that was not confirmed by the multiplex control system. If the circuit is OK, replace the multiplex control unit that monitors the circuit.

Scheme 16

1. Remove the driver's multiplex control unit from the driver's under-dash fuse/relay box.
2. Carefully pry off the driver's door switch trim (see «FRONT DOOR PANEL REMOVAL/INSTALLATION»(ref-174027-S15016844332005051300000) ).
3. Disconnect door multiplex connector A (20P).
4. Check for continuity between A23 terminal of the driver's under-dash fuse/relay box socket and No. 15 terminal of the door multiplex control unit connector A (20P). Is there continuity? YES -Replace the multiplex control unit most closely related to the failure. NO -Repair an open in the wire between the door multiplex connector and the driver's under-dash fuse/relay box. If the wire is OK, replace the driver's under-dash fuse/relay box.

Scheme 17

1. Disconnect driver's multiplex control unit connector B (22P).
2. Disconnect passenger's multiplex control unit connector B (22P).
3. Check for continuity between B1 terminal of the driver's multiplex connector B (22P) and B9 terminal of the passenger's multiplex connector B (22P). Is there continuity? YES -Replace the multiplex control unit most closely related to the failure. NO -Repair an open in the wire between the driver's multiplex control unit connector B (22P) and the passenger's multiplex control unit connector B (22P).

Scheme 18

Scheme 19

1. Remove the driver's multiplex control unit from the driver's under-dash fuse/relay box.
2. Carefully pry off the driver's door switch trim (see «FRONT DOOR PANEL REMOVAL/INSTALLATION»(ref-174027-S15016844332005051300000) )
3. Disconnect door multiplex connector A (20P).
4. Disconnect passenger's multiplex control unit connector B (22P).
5. Check for continuity between No. 15 terminal of door multiplex connector A (20P) and body ground. Is there continuity? YES -Repair short to ground in the wire between door multiplex control unit connector and body ground. NO -Go to step 6.
6. Check for continuity between B9 terminal of passenger's multiplex connector B (22P) and body ground. Is there continuity? YES -Repair short to ground in the wire between passenger's multiplex control unit connector and driver's multiplex control unit connector. NO -Replace driver's multiplex control unit and recheck the symptom.

See also:
• AUTO-OFF HEADLIGHTS CONTROL UNIT INPUT TEST