Multiplex Control System Acura MDX I

Scheme 1

Scheme 2

System Description

The multiplex control system has four internal functions

1. Multiplexing (send 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. Power door locks
9. Power window (including key-off timer operation)
10. Windshield wiper/washer (including speed sensitive intermittent wiper)
11. Security alarm
12. Rear window intermittent wiper
13. Parking brake alarm ('03 model)

Multiplex Communication

To reduce the number of wire harnesses, digital signals are sent via shared multiplex communication lines rather than sending normal electrical signals through individual wires.

1. The input signals from each switch are converted to digital signals at the central processing unit (CPU). The digital signals are sent from the transmitter unit to the receiver unit as serial signals.
2. The transmitted signal is converted to a switch signal at the receiver unit, and it operates the related component.
3. There are exclusive communication lines between each of the multiplex control units: - Door <--> Driver's (between the door and the driver's multiplex control units) wire color: BRN - Driver's <--> Passenger's (between the driver's and the passenger's multiplex control units) wire color: PNK

The control units always communicate via these lines when the system is operating, and they stop communicating when the system is OFF.

Wake-up and Sleep

The multiplex control system has "wake-up" and "sleep" functions to decrease parasitic draw on the battery when the ignition switch is OFF.

1. In the sleep mode, the multiplex control unit stops the functions (communication and CPU control) when it is not necessary for the system to operate.
2. As soon as any operation is requested (for example, door is unlocked), the related control unit in the sleep mode immediately wakes up and begins to function. This control unit also sends a wake-up signal to the other control units via the communication lines.
3. When the ignition switch is turned OFF, and the driver's or front passenger's door is opened and closed, there is about a 15 second delay before the control units go from the wake-up mode to the sleep mode.
4. If any door is open, the sleep mode will not function.
5. If the key is in the ignition switch, the sleep mode will not function.
6. If a door or tailgate key cylinder switch is shorted, the sleep mode will not function.
7. When in the sleep mode, the current draw is reduced from 60-80 mA to less than 20 mA.

Fail-safe

To prevent improper operation, the multiplex control system has a fail-safe function. In the fail-safe mode, the output signal is fixed when any part of the system malfunctions (for example, a faulty control unit or communication line).

Each control unit has a hardware fail-safe function that fixes the output signal when there is any CPU malfunction, and a software fail-safe function that ignores the signal from the malfunctioning control unit and allows the rest of the system to operate normally.

Troubleshooting

Special Tool Required

MPCS service connector 07WAZ-001010A

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

Scheme 4

Scheme 5

Scheme 6

Scheme 7

Scheme 8

Scheme 9

Scheme 10

1. Check the No. 9 (10 A) fuse in the driver's under-dash fuse/relay box and the No. 13 (7.5 A) 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 (A) to the multiplex control inspection connector (B).
3. Turn the ignition switch ON (II). If the driver's seat belt is unbuckled, the seat belt reminder will beep five times. For '04-06 models: Buckle the driver's seat belt or insert the special tool to the multiplex control inspection connector after turning the ignition switch ON (II) for 5 seconds, so seat belt reminder does not overlap MPCS check mode function beeping.
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). MODE 1: IGNITION KEY LIGHT and BEEPER 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. MULTIPLEX CONTROL SYSTEM TROUBLESHOOTING DTC(s) Cause Procedure 1 The driver's unit is unable to receive signals from the door unit. Go to BRN wire communication line test. 2 The driver's unit is unable to receive signals from the passenger's unit. Go to PNK wire communication line test. 3 (Ignore this DTC is vehicle does not have DPMS.) The driver's unit is unable to receive signals from the power seat control unit. Go to PNK wire communication line test. 5 Malfunction in the driver's unit Go to multiplex control system input test, if all inputs are OK, replace driver's multiplex control unit. 6 The door unit is not able to receive signal from the other units. Go to multiplex control system input test if all inputs are OK, replace door multiplex control unit. 7 The passenger's unit is not able to receive signal from the other units. Go to multiplex control system input test, if all inputs are OK replace passenger's multiplex control unit. 8 Power seat control unit is unable to receive signals from the other units. Go to the DPMS input test, if all inputs are OK, replace the power seat control unit. 1, 2, 3 and 5 Simultaneously Communication (BRN or PNK) wire is shorted, (12 V or Ground) Go to shorted communication line test.
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 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 ignition switch ON (II).
10. Check for voltage between A12 terminal of the driver's fuse/relay box socket and body ground. Is there battery voltage? YES - Go to step 11. NO - Repair an open in the wire between the No. 13 fuse in the passenger's under-dash fuse/relay box socket and A12 terminal.
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 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 - Repair an open in the wire between the inspection connector and the driver's under-dash fuse/relay box. If the wire is OK, replace the driver's under-dash fuse/relay box.
14. Check for continuity between the No. 1 terminal of the multiplex 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 11

1. From Mode 1, disconnect the special tool from the multiplex control system (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. Mode 2: Ignition key Light and Beeper 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.
2. Operate the switches as described in the charts below. NOTE: A second key is necessary to test the key cylinder switch. 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. If you continue to hold the power mirror and power seat controls (with DPMS), you will hear beeps as they move through position sensors. PASSENGERS MULTIPLEX CONTROL UNIT Passenger's Multiplex Control Unit Test all the switches in the following order, otherwise the test results maybe inaccurate: Front passenger's door lock knob switch (UNLOCK) Front passenger's door lock switch (LOCK/ UNLOCK) Front passenger's door switch (OPEN) Right rear door switch (OPEN) Right rear door lock knob switch (UNLOCK) Power mirror switch (with DPMS) Security input for the radio or navigation system, RES display, or RES DVD player Test by disconnecting and reconnecting the radio, navigation system, RES display, or RES DVD player connectors DRIVERS MULTIPLEX CONTROL UNIT Driver's Multiplex Control Unit Dash lights brightness controller (ROTATE) Driver's door switch (OPEN) Left rear door switch (OPEN) Left rear door lock knob switch (UNLOCK) Tailgate latch switch (OPEN) Driver's seat belt switch (UNBUCKLED) (1) Windshield wiper switch (in AUTO on Touring or in INT on non-Touring Brake pedal position switch (Brake switch) (PRESSED) Parking brake switch (ON) Hood switch (OPEN) Combination switch (ON) parking lights/head lights (1) '03 model DOOR MULTIPLEX CONTROL UNIT Door Multiplex Control Unit Test all the switches in the following order, otherwise the test results maybe inaccurate: Driver's door lock knob switch (LOCK) Driver's key cylinder switch (LOCK) Driver's door lock knob switch (UNLOCK) Driver's key cylinder switch (UNLOCK) Driver's door lock switch (LOCK/UNLOCK) Power window master switch (for the passenger's windows, not the driver's window) Driving position memory switch (memo, position 1, and position 2) (Touring only) DRIVER'S POWER SEAT CONTROL UNIT (WITH DPMS) Driver's Power Seat Control Unit (with DPMS) Driver's power seat switch (front up/down, rear up/down, side forward/backward, recline forward/backward 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 chart below), or refer to multiplex input test (see «MULTIPLEX CONTROL UNIT INPUT TEST»(/acura/mdx/i-2000-2006/remont/communication-devices/#multiplex-control-system__multiplex-control-unit-input-test) ). SYSTEM System Power door locks (see «KEYLESS RECEIVER UNIT INPUT TEST»(/acura/mdx/i-2000-2006/remont/door-locks-anti-theft-systems/#keylesspower-door-lockssecurity-system) ) Security (Touring) (see «KEYLESS RECEIVER UNIT INPUT TEST»(/acura/mdx/i-2000-2006/remont/door-locks-anti-theft-systems/#keylesspower-door-lockssecurity-system) ) Keyless (Touring) (see «KEYLESS RECEIVER UNIT INPUT TEST»(/acura/mdx/i-2000-2006/remont/door-locks-anti-theft-systems/#keylesspower-door-lockssecurity-system) ) Power windows (Includes key-off timer operation) (see «CONTROL UNIT INPUT TEST»(/acura/mdx/i-2000-2006/remont/windows/#power-windows__control-unit-input-test) ) Entry light control, Key light timer (see «CONTROL UNIT INPUT TEST»(/acura/mdx/i-2000-2006/remont/interiorillumination-lights/#entry-lights-control-system__control-unit-input-test) ) Wiper controls (front and rear) (see «WITHOUT AUTOMATIC WIPER»(/acura/mdx/i-2000-2006/remont/wiperwasher-systems/#wiperswashers__without-automatic-wiper) ) Automatic lights off (Touring) (see «AUTOMATIC LIGHTING CONTROL UNIT INPUT TEST»(/acura/mdx/i-2000-2006/remont/exterior-lights/#exterior-lights) ) Reminder chimes (see «CONTROL UNIT INPUT TEST»(/acura/mdx/i-2000-2006/remont/gauges-instrument-panels/#reminder-systems-key-light-timer-and-engine-oil-pressure-indicator-systems) ) (key-in, seat belt, lights-on) (see «GAUGE INPUT TEST»(/acura/mdx/i-2000-2006/remont/gauges-instrument-panels/#gauges) ) (1) Dash lights brightness control (see «CONTROL UNIT INPUT TEST»(/acura/mdx/i-2000-2006/remont/interiorillumination-lights/#dash-lights-brightness-controller__control-unit-input-test) ) Engine oil pressure indicator (see «CONTROL UNIT INPUT TEST»(/acura/mdx/i-2000-2006/remont/gauges-instrument-panels/#reminder-systems-key-light-timer-and-engine-oil-pressure-indicator-systems) ) (1) '04-'06 models 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 12

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»(/acura/mdx/i-2000-2006/remont/windows/#doors__front-door-panel-removalinstallation) ).
3. Disconnect door multiplex connector A (20P).
4. Check for continuity between A2 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 under-dash fuse/relay box.

Scheme 13

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 door multiplex B (22P) connector and the passenger's multiplex B (22P) connector.

Scheme 14

Scheme 15

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»(/acura/mdx/i-2000-2006/remont/windows/#doors__front-door-panel-removalinstallation) ).
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.

Multiplex Control Unit Input Test

Before performing the multiplex control unit input test, do the multiplex troubleshooting Mode 1 and Mode 2 test.

Scheme 16

1. Remove the passenger's multiplex control unit from the passenger's under-dash fuse/relay box.
2. Inspect the connector and socket terminals to be sure they are all making good contact. If the terminals are bent, loose or corroded, repair them as necessary, and recheck the system. If the terminals look OK, go to step 3.
3. Make the following input tests at the 22P connector B and the passenger's under-dash fuse/relay box socket connector A. Be careful not to spread the fuse box connectors. If any test indicates a problem, find and correct the cause, then recheck the system. If all the input tests prove OK, go to step 1 in «DOOR UNIT»(/acura/mdx/i-2000-2006/remont/communication-devices/#multiplex-control-system) . MULTIPLEX CONTROL UNIT INPUT TEST (PASSENGER'S UNIT) Cavity Wire Test condition Test: Desired result Possible cause if result is not obtained B22 BLK Under all conditions Check for continuity to ground: There should be continuity. Poor ground (G503) An open in the wire A24 Fuse/relay box socket Under all conditions Check for voltage to ground: There should be battery voltage. Blown No. 13 (7.5 A) fuse in the passenger's under-dash fuse/relay box Blown No. 54 (40 A) fuse in the under-hood fuse/relay box Faulty passenger's under-dash fuse/relay box A8 Under all conditions Check for continuity to ground: There should be continuity. Poor ground (G651) An open in the wire A22 Ignition switch ON (II) Check for voltage to ground: There should be battery voltage. Blown No. 9 (10 A) fuse in the driver's under-dash fuse/relay box An open in the wire A12 Under all conditions Attach A12 to battery voltage: Power window relay should click. Check voltage between No. 7 (20 A) passenger's fuse and ground: There should be battery voltage. Poor ground (G651) Faulty passenger's fuse box Faulty power window relay An open in the wire Blown No. 51 (40 A) fuse in the under-hood fuse/relay box

Scheme 17

1. Carefully pry off the driver's door switch trim (see «FRONT DOOR PANEL REMOVAL/INSTALLATION»(/acura/mdx/i-2000-2006/remont/windows/#doors__front-door-panel-removalinstallation) ).
2. Disconnect the connectors (A).
3. Inspect the connector and socket terminals to be sure they are all making good contact. If the terminals are bent, loose or corroded, repair them as necessary, and recheck the system. If the terminals look OK, go to step 4.
4. Make the following input tests at connector A (20P). If any test indicates a problem, find and correct the cause, then recheck the system. If all the input tests prove OK, go to step 1 in «DRIVER'S UNIT»(/acura/mdx/i-2000-2006/remont/communication-devices/#multiplex-control-system) . MULTIPLEX CONTROL UNIT INPUT TEST (DOOR UNIT) Cavity Wire Test condition Test: Desired result Possible cause if result is not obtained A1 WHT/RED Under all conditions Check for voltage to ground: There should be battery voltage. Blown No. 13 (7.5 A) fuse in the passenger's under-dash fuse/relay box Blown No. 54 (40 A) fuse in the under-hood fuse/relay box An open in the wire A2 GRN/WHT Ignition switch ON (II) and passenger's multiplex terminal A12 connected to battery voltage Check for voltage to ground on A2: There should be battery voltage. Blown No. 15 (20 A) fuse in the passenger's under-dash fuse/relay box Faulty power window relay An open in the wire A12 (1) Fuse/relay box socket A12 BLK Under all conditions Check for continuity to ground: There should be continuity. Poor ground (G401) An open in the wire B1 BLK Under all conditions Check for continuity to ground: There should be continuity. Poor ground (G601) An open in the wire (1) Passenger's multiplex control unit connector A

Scheme 18

1. Remove the driver's multiplex control unit from the driver's under-dash fuse/relay box.
2. Inspect the connector and socket terminals to be sure they are all making good contact. If the terminals are bent, loose or corroded, repair them as necessary, and recheck the system. If the terminals look OK, go to step 3.
3. Make the following input tests at 22P connector B and the driver's under-dash fuse/relay box socket connector A. Be careful not to spread the fuse box connectors. If any test indicates a problem, find and correct the cause, then recheck the system. If all the input tests prove OK, one of the multiplex control units (door, driver's or passenger's) must be faulty. Substitute a known-good control unit for the one that's is most closely related to the failure, then recheck. If the symptom continues, replace the next most likely control unit until the symptom goes away.

MULTIPLEX CONTROL UNIT INPUT TEST (DRIVER'S UNIT)

See also:
• KEYLESS RECEIVER UNIT INPUT TEST
• CONTROL UNIT INPUT TEST
• CONTROL UNIT INPUT TEST
• WITHOUT AUTOMATIC WIPER
• AUTOMATIC LIGHTING CONTROL UNIT INPUT TEST
• CONTROL UNIT INPUT TEST
• GAUGE INPUT TEST
• CONTROL UNIT INPUT TEST
• FRONT DOOR PANEL REMOVAL/INSTALLATION
• MULTIPLEX CONTROL UNIT INPUT TEST
• DOOR UNIT