Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
To Enter Mode 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.
- Connect the special tool to the multiplex control system (MPCS) inspection connector (A).
- Turn the ignition switch ON (II). If the driver's seat belt is unbuckled, the seat belt reminder will beep five times.
- After about 5 seconds, the ignition key light should come on and the beeper should beep for 2 seconds, then go off for 0.2 second, then blink and deep for 0.2 second. This indicated that the system is in Mode 1.
Did the multiplex system enter Mode 1?
- YES: Go to step 5.
- NO: Go to step 6.
- Check for a DTC.
- If there is no DTCs present:
The ignition key light and beeper will not blink/beep again after the Mode 1 indication.
- If there are DTC(s) 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 ascending order.
Is there a DTC present?
- YES: Follow the procedure in the chart below.
- NO: Go to Mode 2 (see Mode 2 ).
- If there is no DTCs present:
- Remove the special tool from the MPCS inspection connector.
- Remove driver's multiplex control unit from the driver's under-dash fuse/relay box.
- Check for voltage between the No. 12 terminal of the driver's fuse/relay box socket and body ground.
Courtesy of AMERICAN HONDA MOTOR CO., INC.
Is there battery voltage?
- YES: Go to step 9.
- NO: Replace the driver's under-dash fuse/relay box.
- Turn ignition switch ON (II).
- Check for voltage between No. 24 terminal of the driver's fuse/relay box socket and body ground.
Courtesy of AMERICAN HONDA MOTOR CO., INC.
Is there battery voltage?
- YES: Go to step 11.
- NO: Repair an open in the wire between No. 13 fuse in the passenger's under-dash fuse/relay box and the driver's under-dash fuse/relay box socket.
- Check for continuity between No. 14 terminal of the driver's under-dash fuse/relay box socket and body ground.Fig 6: Checking Continuity Between No. 14 Terminal Of Driver's Under-Dash Fuse/Relay Box Socket & Body Ground
Courtesy of AMERICAN HONDA MOTOR CO., INC.
Is there continuity?
- YES: Go to step 12.
- NO: Repair an open in the wire between driver's multiplex control unit and body ground. If the wire is OK, check for poor ground at G401.
- Check for continuity between No. 11 terminal of the driver's multiplex control unit connector B (22P) and body ground.Fig 7: Checking Continuity Between No. 11 Terminal Of Driver's Multiplex Control Unit Connector B (22P) & Body Ground
Courtesy of AMERICAN HONDA MOTOR CO., INC.
Is there continuity?
- YES: Go to step 13.
- NO: Repair an open in the wire between driver's multiplex control unit connector B and ground. If the wire is OK, check for door ground at G501.
- Check for continuity between No. 1 terminal of the MPCS inspection connector and the No. 15 terminal of the driver's under-dash fuse/relay box socket.Fig 8: Checking Continuity Between No. 1 Terminal Of MPCS Inspection Connector & No. 15 Terminal Of Driver's Under-Dash Fuse/Relay Box Socket
Courtesy of AMERICAN HONDA MOTOR CO., INC.
Is there continuity?
- YES: Go to step 14.
- NO: Repair an open in the wire between the MPCS 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.
- Check for continuity between No. 3 terminal of the MPCS inspection connector and body ground.
Courtesy of AMERICAN HONDA MOTOR CO., INC.
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.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.