Rick's Free Auto Repair Advice

Honda door locks cycling

Diagnose and fix Honda door locks cycling

Honda door lock cycling is a fairly common problem where the door locks will lock and unlock without any input from you or the passengers. Most of the time the problem is with a poor ground connection in the driver’s door switch, a bad switch or a wiring harness issue.

How Honda door locks work

The door lock switches don’t actually switch power to the door lock actuators. The switches act as an input signal to the multiplex integrated control unit (MICU), which contains the actual relays to operate the power door locks.

Each Honda door lock switch has three wires; an unlock wire, Honda door lock switcha lock wire and a ground wire. The MICU provides power to both the unlock and lock terminals of the door lock switch. When you operate the switch, it connects the power to ground and the MICU sees a voltage drop. That’s its signal to either lock or unlock the doors. The MICU then grounds the unlock or lock relay coil circuit which energizes the door lock actuator. Depending on the year, make, model of your Honda, the door lock relays may be separate or built into the MICU

What goes wrong with Honda door locks

• Bad ground connection at the driver’s door lock switch

• Bad driver’s door lock switch that intermittently grounds the unlock or lock contacts

• Bad door lock actuator

• Bad MICU or intermittent MICU ground

Many times shops find that the ground terminal in the electrical connector to the driver’s door lock switch isn’t making good contact. So start by removing the door lock switch and using a computer safe test light to check for a good ground connection on the black wire terminal in the electrical connector.

Reconnect the electrical connector to the door lock switch. Next, backprobe either of the two powered unlock/lock wires and check for power using a digital multimeter. You should see power on both wires. Then move the switch operate the unlock or lock function. When you do that, you should see almost a full voltage drop on the powered wire. If you don’t, either the switch is bad or there’s still a problem with the ground connection.

If everything checks out, you’ll need a scan tool to see if the MICU is seeing the door lock input from the door lock switch. If the MICU isn’t seeing the door lock input when you operate the switch, the problem is in the wiring harness between the door lock switch and the MICU. If the MICU is seeing the input but still not operating the lock actuators, chances are the MICU is bad

©, 2019 Rick Muscoplat

Posted on by Rick Muscoplat


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