The starter motor on my son’s 2007 Audi A3 had reached the end of its workable life, and the car would no longer start. So I purchased a replacement from RockAuto.com which was delivered promptly. As a novice / weekend Mr. Fixit I set about removing the old starter motor. The positioning was awkward, but I managed to unplug the connector and remove the two mounting bolts.

I compared the new starter with the old and everything matched up well so I started to fit the new starter. The connector plug was a little tricky, feeling stiff, and I had some challenges fitting it. After attempting a few times and applying a little dielectric grease the connector seemed to click in. I fitted the supporting bolts, checked over everything, and all looked good.

Feeling proud of myself I jumped into the car, turned the key … nothing. Did I miss something? Had I misdiagnosed - was it the alternator instead? I tried a few more times with the same result. Dash lights were working, headlights were fine, radio and all electrical components were working fine. What could it be?

After removing and reinstalling the starter, I was still unable to start the vehicle. So after having the vehicle towed to the local shop, the mechanic called me a few minutes later chuckling. “The pin inside the connector plug was bent and you weren’t getting any connection!” It was a simple fix to straighten the internal pin. I sheepishly drove away from the shop, but happy the issue had been solved. A valuable lesson learned. Check the internal connection!

Danny in Ontario, Canada

The window does not close all the way when the door is shut. The transmission shifts itself into park. The door lock stops working. The dome light will not turn on or never turns off. Any of these problems may be a symptom of a failing door latch.

The door latch on a car built during the previous century is typically a mechanical hook that grabs onto a striker plate bolted to the door frame. Dome and other interior lights have their own electrical switches (spring loaded, mercury switch...) mounted elsewhere on the door or door frame. Power lock actuators are separate from the door latch as well.

The door latches on modern cars combine all the functions of a traditional latch with a bunch of electrical parts that used to be scattered around the door. The electric door lock actuator motor, dome light switch, door ajar switch and more are all bundled into the door latch assembly.

Having a Swiss-Army-Knife door latch design that does nearly everything must lower costs for the car manufacturers, but how they saved money on parts is not necessarily obvious because the latches are quite complex. There is typically not just one switch that tells all the computers the door is open or closed. Some systems like interior lights and window closing (window opens slightly to vent air and then closes when the door is shut) need to have electrical power and function even if the key fob is not present.

Various views of a 2014-2020 Acura MDX Door Lock Actuator

Close examination of modern door latches reveals many of them are a bundle of electrical switches. Parallel to the big latch that grabs the door striker there may be plastic cams that turn on/off switches. Moving the plastic cams by hand may reveal which switch turns on/off what function. For example, I found I could turn on/off my Dodge Challenger's trunk light by flipping the switch in the trunk latch. (This comes in handy when the trunk lid is left open while charging its trunk-mounted car battery.)

All the mechanical movement of cams in the door latch means components wear and/or get jammed by dirt or ice. Sometimes cleaning and lightly lubricating a door latch assembly will get its switches and motors working again. Eventually something will wear out, and the whole door latch assembly must be replaced, but typically the job is not any harder for a DIYer than replacing a door lock actuator or door latch on an older car. The assembly may be more expensive, but it includes more new parts so there may be less need to take off the door panel and replace something else any time soon.

Look under "Body & Lamp Assembly" in the RockAuto.com catalog to see door latch assemblies for your specific vehicle under Door Lock Actuator, Trunk Lock Actuator, Trunk Lid / Tailgate Pull Down Actuator and/or Door Latch.

Tom Taylor,
RockAuto.com

To read more of Tom's articles, click this link and choose from story titles on the Newsletter Archives page.

RockAuto is excited to announce the addition of three new hoodies! They feature a midweight material with a jersey-lined hood, and front pouch pocket for comfort and warmth.

Shop all RockAuto Apparel & Gifts in the "Tools & Universal Parts" tab of the RockAuto.com Catalog.