Q: I have recently experienced a problem with the security lock system in my 2001 Lexus RX 300. It appears that the master sensor in my car does not work, but the rest of the locks work fine. I have to manually insert the key to lock the door.

I took the car to a mechanic, and he wanted more than $500 to change the master sensor, located on the driver-side door, to correct the problem. That seemed a lot of money. Is there a way I can do it, if I know what parts I need to repair it?

— Ralph Lee

A: Ralph, it sounds like your Lexus is suffering from a faulty driver’s door power door lock actuator. This part is a small reversible electric motor that pushes and pulls on the door latch’s locking mechanism and is unfortunately integrated into a very expensive door latch/lock/actuator assembly ($354 list price, available online for about $250). Replacement isn’t particularly difficult once the door trim panel is removed — the published labor time is a little less than an hour.

Renewing the assembly is the traditional way to take care of this, but I do have a slightly kooky option, should you be inclined to tinker a bit. While researching your situation, I stumbled across a few folks who had also balked at the price of the Lexus part and, with a little home engineering, grafted a $5 universal door-lock actuator motor to the Lexus latch, and voila.

I’ve used these actuators, purchased on eBay and elsewhere, for several projects; one is a solar-powered, automatic cat-food dispenser with more than 900 flawless operating cycles to date. For such an inexpensive price, these little servo-motors are amazing. The folks who retrofitted their Lexus left the original actuator in place and connected a push rod from the latch to the new actuator (bracket and push rod are included with the part).

This requires some head-scratching and a few holes to be drilled to mount the new part within the door. The two wires connected to the original actuator are transferred to the replacement unit — reverse them as needed for correct actuator direction — and the new actuator pushes/pulls the intact original assembly lever with moderate ease.

Component integration has become a widespread practice on modern automobiles. What used to be perhaps three or four individual components are often combined into a single assembly. This makes sense from a manufacturing standpoint as it saves weight, space, assembly time and cost, and often improves reliability.

An assembly’s replacement price can be tough to swallow as a consumer when service is needed, but I try to remember to look at the whole car. Integration and cost savings in one place allows money to be better spent in other places, giving us some amazingly safe, efficient and gadget-filled cars at only a slight premium in inflation-adjusted dollars over cars of the past.

One might criticize the idea of modifying such an exquisite car with a home-generated solution, but if it’s done safely and effectively and is invisible to the eye, it beats paying about five times what the original part is worth. Also, it feels really good to fix something, as opposed to just replacing parts.