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Multiplex Control System Acura RSX I

Communication Devices 6 illustrations ~2574 words

Scheme 1

Scheme 1: Component Location Index
Scheme 1: Component Location Index

Scheme 2

Scheme 2: Circuit Diagram
Scheme 2: Circuit Diagram

Scheme 3

Scheme 3
Scheme 3

System Description

The multiplex control system has four internal functions

  1. Multiplexing (sends multiple signals over shared wires)
  2. Wake up/sleep (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 these circuits

  1. Entry light control (ignition key light and ceiling light)
  2. Wiper/washer (intermittent wipe and park functions)
  3. Interlock system
  4. Keyless/power door lock
  5. Gauge assembly, temperature gauge, and indicator lights
  6. HVAC (compressor and fan control)
  7. Key-in reminder
  8. Lights-on reminder
  9. Seat belt reminder

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).
  2. The digital signals are sent from the transmitting unit to the receiving unit as serial signals.
  3. The transmitted signal is converted to a switch signal at the receiving unit, and it operates the related component or monitors a switch.
  4. There are exclusive communication lines between the ECM/PCM, the gauge assembly, the keyless control unit, and the under-dash fuse/relay box.

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 functioning (communication and CPU control) when it is not necessary for the system to operate.
  2. As soon as any operation is requested (for example, a door is unlocked), the related control unit in the sleep mode immediately wakes up and begins to function.
  3. When the ignition switch is turned OFF, and the driver's or front passenger's door is opened, then closed, there is about a 40 second delay before the control unit goes from the wake-up mode to the sleep mode.
  4. If any door is open, the sleep mode will not function.
  5. If a key is in the ignition switch, the sleep mode will not function.
  6. When in sleep mode, the draw is reduced from 70-80 mA to less than 10 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 system to operate normally.

Troubleshooting

Special Tools Required

MPCS service connector 07WAZ-001010A

Mode 1 Test

Note. Check for ECM/PCM DTC(s). Troubleshoot and repair the cause for the DTC(s) first.

Scheme 4

Scheme 4: Mode 1 Test
Scheme 4: Mode 1 Test

Scheme 5

Scheme 5
Scheme 5
  1. Remove the driver's dashboard lower cover (see «DRIVER'S DASHBOARD LOWER COVER REMOVAL/INSTALLATION»(/acura/rsx/i-2001-2004/remont/exteriorinterior-trim/#dashboard) ).
  2. Check the No. 9 (10 A) fuse in the underhood 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 3. NO - Find and repair the cause of the blown fuse.
  3. Turn the ignition switch ON (II). If the driver's seat belt is unbuckled, the seat belt reminder will beep 6 times.
  4. Set the ceiling light to the middle position and close all the doors.
  5. Connect the special tool (A) to the multiplex inspection connector (B). MODE 1: Ignition key light and ceiling light
  6. After about 5 seconds, the ignition key light and ceiling light should come on for 2 seconds, go out, then blink on for 0.2 second to show the system is now in Mode 1. Did the ignition key light and ceiling light indicate mode 1? YES - Go to step 8 . NO - Go to step 7.
  7. Check for continuity between the No. 4 terminal of the under-dash fuse/relay box connector J and body ground. Is there continuity? YES - Replace the under-dash fuse/relay box. NO - Repair the open in the wire. If the wire is OK, repair G301.
  8. If there are any DTCs present, the ignition key light and ceiling light will blink to indicate the DTC(s). If more than one DTC is present, the DTCs will be displayed in ascending order. If there are no DTCs, the ignition key light and ceiling light will not blink again after the Mode 1 indication. Are there any DTCs? YES - Go to step 9. NO - Go to Mode 2 Test (see «MODE 2 TEST»(/acura/rsx/i-2001-2004/remont/communication-devices/#multiplex-control-system__mode-2-test) ).
  9. Troubleshoot the DTC(s) in the order indicated using the following charts. If a faulty control unit is suspected, substitute it with a known-good part and recheck for DTCs. If the DTC(s) is still present, go to the next step listed for the DTC. If the DTC(s) is no longer present, replace the original part. Individual DTCs INDIVIDUAL DTCS Multiplex DTC Probable Cause 1 The multiplex control unit cannot receive signals from the gauge assembly. Faulty power or ground to the gauge assembly Faulty gauge assembly Faulty under-dash fuse/relay box 2 The multiplex control unit cannot receive signals from the ECM/PCM Faulty power or ground to the ECM/PCM Faulty ECM/PCM (1) Faulty under-dash fuse/relay box 3 Internal failure of the multiplex control unit Faulty under-dash fuse/relay box 5 The gauge assembly cannot receive signals from the ECM/PCM Faulty power or ground to the ECM/PCM Faulty gauge assembly 6 The ECM/PCM cannot receive signals from the multiplex control unit and the gauge assembly Faulty power or ground to the ECM/PCM Faulty gauge assembly (1) Before replacing a faulty ECM/PCM, make sure it has the latest software revision. Update if necessary before swapping or replacing. Multiple DTCs MULTIPLE DTCS Multiplex DTCs Probable Cause 1,2 and 3 & ECM DTC P0600 Simultaneously Short to ground on one of the communication wires. Short to ground on the YEL wire between the ECM/PCM terminal E24 [E13] and the under-dash fuse/relay box terminal E10 Short to ground on the WHT/GRN wire between the gauge assembly terminal B13 [B11]and under-dash fuse/relay box terminal K10 1 and 6 Simultaneously Open in the communication wire Open in WHT/GRN wire between the under-dash fuse/relay box terminal K10 and the gauge assembly terminal B13 [B11] 2 and 5 Simultaneously Open in the communication wire Open in the YEL wire between the under-dash fuse/relay box terminal E10 and ECM/PCM terminal E10 and ECM/PCM terminal E24 [E13] [ ]: '05-06 models

Mode 2 Test

  1. From mode 1, disconnect the special tool from the multiplex inspection connector for 5 to 10 seconds, and then reconnect it.
  2. The ignition key light and ceiling light should come on for 2 seconds, go out, then blink twice, 0.2 seconds each time. The system is now in Mode 2.
  3. Operate the switches listed below: If the circuit is OK, the ignition key light and ceiling light will blink once. If the circuit is faulty, the lights will not blink. Tip: Operating the switches most closely related to the problem you are diagnosing is a quick way of testing the circuits integrity. MODE 2 TEST Switch Lights blink when: Windshield washer switch Washer switch pulled Windshield wiper switch Switch in the INT position Driver's door switch Driver's door is opened Passenger's door switch Passenger's door is opened Hatch latch switch Hatch is opened Parking brake switch Parking brake applied Driver's door lock switch Pushed to lock and unlock Driver's door knob switch Knob in UNLOCK or LOCK position A/C switch A/C switch ON and blower switch ON Headlight switch Switched to the PARK position Brake pedal position switch Brake pedal pressed Transmission range switch Shift P, R, D, D3 (A/T) Upshift then downshift (M/T)
  4. If all inputs were confirmed, or multiple circuits failed at the same time in Mode 2, go to the «MULTIPLEX SLEEP MODE TEST»(/acura/rsx/i-2001-2004/remont/communication-devices/#multiplex-control-system__multiplex-sleep-mode-test) . If a single switch fails in Mode 2, troubleshoot its circuit.

Multiplex Sleep Mode Test

  1. Connect the positive lead of a voltmeter to terminal No. 10 of the under-dash fuse/relay box connector E (YEL) or K (WHT/GRN) and the negative lead to body ground.
  2. Connect an ammeter between the negative battery cable and the negative battery post.
  3. Remove the special tool from the multiplex inspection connector.
  4. Close the doors, the hatch, turn the headlights off, turn the ignition switch OFF and remove the key.
  5. Within 1 minute, the voltage on the communication wire (E10 or K10) should change from about 4-10 V to battery voltage and the amperage at the negative battery terminal should drop from about 70-80 mA to less than 10 mA.
  6. Record your findings and go to the «MULTIPLEX WAKE-UP MODE TEST»(/acura/rsx/i-2001-2004/remont/communication-devices/#multiplex-control-system__multiplex-wake-up-mode-test) .

Multiplex Wake-up Mode Test

  1. From the Sleep Mode, wake-up the multiplex system by performing one of the following operations: OPERATION SPECIFICATION Operation Method used for wake up Cycle ignition switch ON (II) All multiplex units wake up simultaneously (regardless of ability to communicate) Turn combination light switch to parking light position Multiplex control unit wakes up the other units via communication lines. Open the driver's door Multiplex control unit wakes up the other units via communication lines.
  2. As the system shifts to its Wake-up (Active) Mode, communication wire voltage will return to 4-10 V and the battery terminal current will return to 70-80 mA.
  3. If the system does not go into Sleep Mode or Wake-up Mode properly, perform the Multiplex Control Unit Input Test (see «MULTIPLEX CONTROL UNIT INPUT TEST»(/acura/rsx/i-2001-2004/remont/communication-devices/#multiplex-control-system) ). NOTE: If multiple circuits fail to respond in the Mode 2 tests and/or the multiplex circuit fails to go into Sleep Mode or Wake-up Mode, it may mean that a control unit failed without triggering a DTC in Mode 1. Perform the Multiplex Control Unit Input Test (see «MULTIPLEX CONTROL UNIT INPUT TEST»(/acura/rsx/i-2001-2004/remont/communication-devices/#multiplex-control-system) ). If the input test confirms that all the inputs are working properly, substitute a known-good multiplex control unit, gauge assembly or ECM/PCM, one at a time. If the system works properly after swapping one of the above components, replace the original component.

Scheme 6

Scheme 6: Multiplex Control Unit Input Test
Scheme 6: Multiplex Control Unit Input Test
  1. Remove the driver's dashboard lower cover (see «DRIVER'S DASHBOARD LOWER COVER REMOVAL/INSTALLATION»(/acura/rsx/i-2001-2004/remont/exteriorinterior-trim/#dashboard) ).
  2. Disconnect the under-dash fuse/relay box connectors C, E, F, J, K, 0, P, Q, X and Y. NOTE: All connectors are wire side of female terminals.
  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. With the connectors still disconnected, make these input tests at the connector. 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 5. CAVITY TEST CONDITION SPECIFICATION Cavity Wire Test condition Test: Desired result Possible cause if result is not obtained J4 BLK Under all conditions Check for continuity to ground: There should be continuity. Poor ground (G301) An open in the wire Y6 BLK Under all conditions Check for continuity to ground: There should be continuity. Poor ground (G401) An open in the wire Y1 BLK Under all conditions Check for continuity to ground: There should be continuity. Poor ground (G401) An open in the wire
  5. Reconnect the connectors to the under-dash fuse/relay box, and make these input tests at the appropriate connectors on the under-dash fuse/relay box. If any test indicates a problem, find and correct the cause, then recheck the system. If all the input tests prove OK, the multiplex control unit must be faulty, replace the under-dash fuse/relay box assembly. CAVITY TEST CONDITION SPECIFICATION Cavity Wire Test condition Test: Desired result Possible cause if result is not obtained J2 WHT/RED Under all conditions Check for voltage to ground: There should be battery voltage. Blown No. 9 (7.5 A) fuse in the underhood fuse/relay box An open in the wire Q3 GRN Driver's door open Check for voltage to ground: There should be 1 V or less. Faulty driver's door switch An open in the wire Driver's door closed Check for voltage to ground: There should be 5 V or more. Faulty driver's door switch Short to ground Q4 LT GRN/RED Passenger's door open Check for voltage to ground: There should be 1 V or less. Faulty passenger's door switch An open in the wire Passenger's door closed Check for voltage to ground: There should be 5 V or more. Faulty passenger's door switch Short to ground Q8 C8 F1 GRN/ORN GRN/ORN GRN/RED Parking brake lever up Check for voltage to ground: There should be 1 V or less. Faulty parking brake switch An open in the wire Parking brake lever down Check for voltage to ground: There should be 5 V or more. Faulty parking brake switch Short to ground Q5 BLU/RED Ignition switch ON (II) driver's seat belt is unbuckled. Check for voltage to ground: There should be 1 V or less. Faulty driver's seat belt switch Poor ground (G551) An open in the wire Q6 BLU/RED Ignition switch ON (II) driver's seat belt is buckled. Check for voltage to ground: There should be 5 V or more. Faulty driver's seat belt switch Short to ground P18 RED Hatch open Check for voltage to ground: There should be 1 V or less. Faulty hatch latch switch Poor ground (G701) An open in the wire Hatch closed Check for voltage to ground: There should be 5 V or more. Faulty hatch latch switch Short to ground X5 RED/WHT Ignition key is in the ignition switch Check for voltage to ground: There should be 1 V or less. Faulty ignition key switch Poor ground (G401) An open in the wire Ignition key is out of the ignition switch Check for voltage to ground: There should be 5 V or more. Faulty ignition key switch Short to ground X8 WHT/BLK Under all conditions Attach to ground: The ignition key light should come on. Blown No. 3 (7.5 A) fuse in the underhood fuse/relay box Blown LED An open in the wire O7 GRN/RED Ceiling light switch in the middle position, all doors closed Attach to ground: The ceiling light should come on. Blown No. 3 (7.5 A) fuse in the underhood fuse/relay box Faulty ceiling light An open in the wire C11 BLU Under all conditions Attach to ground: Dash lights should come on. Blown No. 2 (15 A) [No. 2 (10 A)] fuse in the underhood fuse/relay box Faulty taillight relay An open in the wire F8 GRN/RED Brake fluid reservoir float in down position (brake fluid removed) Check for voltage to ground: There should be less than 1 V. Faulty brake fluid level switch An open in the wire Brake fluid reservoir float in up position (brake fluid at full level) Check for voltage to ground: There should be 5 V or more. Faulty brake fluid level switch Short to ground E10 YEL Under all conditions Check for voltage to ground: There should be battery voltage in the sleep mode and 3-7 V when awake. An open or short in the wire K10 WHT/GRN Under all conditions Check for voltage to ground: There should be battery voltage in the sleep mode and 3-7 V when awake. An open or short in the wire [ ]: '05-06 models