I recently took my Yukon XL to my GMC dealer for an oil change and to find out why the engine light was on.

I’m a loyal customer. I bought the vehicle there, and I’ve always had it serviced at the dealership, even knowing the oil change costs more and takes longer than at a local quick-change outlet. This time the service writer also recommended, based on my mileage, I get the transmission fluid changed. I didn’t plan on spending for that, but I took his advice.

Then I lost it. He had me sign the work estimate and parenthetically noted there’s a charge of $39.95 to determine why the engine light was on.

“Are you serious,” I asked. “What’s with that?”

His first answer was a gem: “We have to pay our mechanic for the time to determine why the light is on.”

“Don’t you think you’d look at that as just a cost of doing business with a regular customer like me?” I countered.

His next defense did me in: “No. Look, we have to charge that because when we tell you why the light is on, you could go down to some local mechanic to get it fixed.” And it would be a lot cheaper, I said to myself, but I’m obviously a loyal customer.

Not feeling like a valued customer and pissed about it, I complained. He didn’t respond, so I grudgingly signed and headed for the waiting room. That’s when I recalled an old list of steps that, as a good representative of the dealership, he could have taken to turn my displeasure around.

• Don’t become defensive. Instead of defending the charge and being obviously irritated by my complaint, he could have focused on the problem and demonstrated a commitment to good customer service by offering something like: “I’m sorry you have a problem with this, so let me see if there is anything we can do about it.”

• Listen before speaking. Allow the customer to explain his or her view of the problem — for example, I bought the vehicle here, and always service it here. There are no grounds to think the vehicle would be taken to another mechanic. Listen carefully.

• Has the customer clearly explained the complaint? Before suggesting anything, make certain you understand exactly what is upsetting the customer. If it’s not clear, ask again. Do not assume or jump ahead of the customer.

• Ask for the customer’s help. When a resolution isn’t immediately obvious, you can always ask: “What do you think would be a fair solution?”

• Always keep promises. Don’t promise to do more than you have the authority to do, but do what you say you will do. If you need to go higher up, tell the customer you absolutely want to solve his problem, but you’ll have to get back to him ASAP.

Customer loyalty is not automatic, so it’s critical that everyone in the dealership works to nurture it. That’s why every customer should be considered gold by every member of the team at every level. In this example, simply not becoming defensive would have diffused the situation by indicating that some attempt would be made to fairly solve the problem.

In the end, the $39.95 charge was taken off my bill because the cost of the repair was considerably higher. But here’s the real truth: The episode wasn’t pleasant, and it may very well affect my sense of loyalty going forward.

Think about it — that 40 bucks pales in comparison to the lost revenue if I, as a good customer, decide to buy my next vehicle from another dealership.