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Check Engine Light mystery: "LDC"?

Has anyone heard of an “LDC”?

I took my car in to have the codes pulled for a check engine light. Eight hours and $160 later, mechanic’s receipt says, “Diagnostic OK. Test shows faulty LDC. Misfire in all 4 cylinders. Replace LDC. Road test. Misfire reoccurs - Cylinder 4 Only”.

Parts (“LDC LEG shop supplies”) = $41; Labor = $108; Hazardous Materials = $1.62.

Took it home and nothing to show for the time and $$: idle is MUCH worse than it was before I took it in. Check Engine light stayed on for a few days (mechanic said there was a second code that he wasn’t able to diagnose and I would have to bring the car back again) then went off by itself.

Googled “LDC” - found nothing anywhere related to car parts. Spoke to mechanic at Honda shop - never heard of an LDC.

Does anyone have any insights? Is this a sham? Thanks so much for any ideas.

Why have you not asked the shop to explain what LDC is and what do they plan to do since you still have problems.


Maybe treat it as a puzzler. hmmm … since it only took an hour, must be something cheap & easy to replace. The LEG seems like a clue, but have no idea what that refers to.

LDC could means Leak Down Compression Test. Not sure how you’d replace it though, since it isn’t a part. I’m thinking it is some part that detects a lean condition.

Other things the L could mean

Labor … as it happens when the engine is being labored
Leading … could pertain to ignition timing
Lean … that could at least cause a misfire
Left … pertaining to the left side of the car
Long … as in long distance …
Limited … as in limited slip differential
Limp … as in limp mode
Load … as in engine load
Lock … as in lock up torque converter
Low … as in low pressure side of A/C system

What makes you assume I did not ask them?

The shop did give me a definition of the acronym at the time but I forgot - it didn’t make any sense to me, but I guess I’m too trusting: given my relative lack of knowledge of auto mechanics, I want to assume that my mechanic knows what he’s doing. Since symptoms were worse when I got home, I tried (several times) to call back, and left a message on his website. He does not pick up the phone and has not returned my messages (4 days later).

Sound’s about time to get a new mechanic.

Unless I’m in the middle of a brain freeze, I can’t think of what an LDC is.
The labor seems awful cheap for 8 hours of time; assuming an actual 8 hours was spent working on the car.

The first thing I would suggest doing since there is apparently only a Cylinder 4 misfire would be to run a compression test.If the pressure is low on that cylinder I would follow it up with a wet compression test to verify if the problem is an exhaust valve which has tightened up. That’s not an unheard of problem on engines with mechanical valve lifters.
Valve lash should be inspected every 30k miles but his is seldom ever done.

Here’s an idea, it isn’t LDC, the letters were transposed, they meant to type DLC === data link connector. That’s the gadget the tech plugs their scan tool into, in order to read the diagnostic codes and run various tests. That would have to work in order to have much of a chance to diagnose misfires in an OBD II engine.


Seriously considering - but how do you find a good one??? I have had terrible luck in this area. All of the mechanics around here recommended in the CarTalk Mechanics files have only one or two ratings, which is meaningless. And forget Angie’s List – that’s where I found the people I’m struggling with right now.

Thank you - these sound like good suggestions. Maybe if I make them to the next mechanic I go to, s/he will assume I know what I’m talking about and not rip me off.

Hmmm, interesting thought. The invoice says, “Diagnostic test shows faulty LDC. Misfire in all four cylinders.” I was assuming that implied a cause and effect – you’re suggesting they are two unrelated statements?

Another question for you all: if they purchased a part for replacement, shouldn’t they have a sales receipt for it that they can produce? (It wasn’t in stock - they specifically said that they had to wait for it to come in, which is why the car was sitting in the shop all day.)

Ask people you know friend’s family member’s coworker’s people at your church people in your neighberhood etc.

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Good advice by @Renegade above re finding a good shop. Beyond that, after you eliminate the ones that don’t work on Hondas, or are too far away, etc, interview the rest and ask them some simple questions like “what is your hourly labor rate”, “do you have the Honda factory scan tool”, “do you subscribe to the Honda service data”, “do you keep a file off all the work you’ve done on my car”, etc. You don’t need to get a perfect answer on those, but you should come away feeling they have a lot of experience and success working on Honda’s. Once you decide on a particular shop, schedule a general inspection, but first let them know who recommended you to them; they’ll take an hour and go over your car top to bottom looking for signs of upcoming problems, inventory the scheduled maintenance situation, and provide you suggestions on what the high priority items that need to be done now, and which can be deferred. It will cost you $100 or so for that, but money well spent imo. Plus you get off on a good foot with the shop, they’ll have started a file and can consult that, and when your Honda does need a repair they’ll have a good base to start the diagnosis.

One other thing, while you suggest you’ve felt cheated in the past, cheating customers by a shop isn’t a common thing reported here. When the customer isn’t satisfied, it’s usually a combination of poor communication skills by the shop and impossible expectations by the customer. Cars these days are very complicated. The owner can’t expect the shop will be able to fix the problem on the first go-a-round. It’s an iterative process in many cases. But you can expect them to keep you informed of the progress, come up with work-a-rounds in the meantime, and most important, to continue to work on the problem until you are satisfied with the results.

A faulty DLC could potentially cause misfires. That’s the electronic communication hub the engine computer uses to gather and process sensor information, and it needs that info to fire the spark plugs, inject the fuel, and run the engine correctly.

Perhaps, but they wouldn’t give that to the customer usually, they’d keep that for their expense records. They also might consider the price they pay and the vendor they use to be confidential information. You have the right to ask the give you the removed part if you want, but do that in advance, not when you come back to pick up the car as they might have already thrown it away by then.

Thank you George - excellent advice. And Renegade, I agree - I have talked to friends about recommendations but I need to follow through.

What a great community we have here - I wish I had discovered it sooner.

I tend to think you need another mechanic. It’s odd that your current place would perform this work and then hand your car back to you with a Cylinder 4 misfire and no reason for the No. 4 misfire.

Has this car been running ragged for quite a while before going to the shop or possibly a subtle misfire which got worse?

“Perhaps, but they wouldn’t give that to the customer usually, they’d keep that for their expense records. They also might consider the price they pay and the vendor they use to be confidential information. You have the right to ask the give you the removed part if you want, but do that in advance, not when you come back to pick up the car as they might have already thrown it away by then.”

All true. More than one poster here has considered the completely normal process of mechanics charging retail for a part they purchased at a lower price is ripping them off. Do they think the apple they buy at the grocery costs them the same as the store paid?