Should new car come w/a diagnosis baseline?

In Ray’s column this week, he is helping a reader w/a difficult to diagnose engine problem, thought at first to be caused a dirty air flow sensor (MAF). Cleaning/replacing the sensor didn’t help. Ray now thinks it is caused be something else, of undetermined origin. Very frustrating situation for the car owner of course. I got to thinking, what if the car owner (or their shop) had a set of baseline sensor data to compare against? The folks at the factory, before shipping the car to the dealership, would drive the car along a known route on a test track, at a range of speeds, then record all of the pertinent sensor data. Then they’d (somehow) provide that data to the new car owner as a baseline of what the sensor data should be for that drive.

If the reader had this set of sensor data, they could make the same drive and compare what they measure now, to what it was when the car was new. Seems quite likely whatever issues are causing the problem would be immediately apparent by comparing the before & after sensor data.

Good idea? Bad idea? Wouldn’t make much difference in most cases?

Would make no difference. Cars are delivered “in spec”. The sensor readings that go out of spec is evidence of the problem. It takes a skill diagnostician following a trouble tree published by the manufacturer and using their own experience to find the problem. Sadly, there are fewer and fewer of those.

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We have that already. It’s called talent and experience.

My doctor can look at an x-ray and see what’s wrong, whereas I have no idea what he’s looking at. On the other hand, if an engine is running poorly, more than likely I can figure out the cause by simply looking at some data on a laptop.


I always measure my A/C outlet temperature when I get a new car so that I have a number for comparison later if I suspect that my A/C isn’t working as well as it should.

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I understand what you mean and I agree, but don’t depend on your doctor to read X-rays. You are much better off if a radiologist reads them. Alabama Governor George Wallace was shot at a shopping center in Silver Spring, MD while he was running for President. He was taken to the National Institutes of Health (NIH) for evaluation and surgery. His doctor insisted on reading the X-rays himself. The staff radiologists looked at the X-rays later and found a bullet at the base of Wallace’s spine that wasn’t found by the doctor and consequently wasn’t removed. Wallace may have achieved some or full mobility if that bullet had been removed. Doctors can be very good at what they do, but are not good at everything.

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What about temperature, altitude, etc etc… Then what, ship your vehicle cross country back to the manufactures so they can make the same drive and compare notes??

As already mentioned, it’s called mechanics doing proper diagnostics with the proper tools…

Doctor, radiologist. Service writer, mechanic. What’s the difference? :smile: :smile:

The ambient air temp would be measured by the IAT sensor, and the altitude by the MAP. I expect the differences in the other sensor readings between when the engine was running poorly for unknown reasons later, vs new at the factory wouldn’t depend too much on those parameters, given the car’s performance relating to temperature is mostly determined by the coolant temperature. If there was a significance difference in altitude, you would need to apply some common sense adjustments to the expected intake airflow data. In any event, a good deal of critical diagnostic info would present itself just in the warm up period, idling in the driveway.

If it were easy for car owners with difficult to diagnose symptoms to find a mechanic who know how to do the proper diagnostics each and every time, what is the purpose of Ray’s Dear Car Talk column?

All cars come with a diagnosis baseline-the normal readings for each sensor. I don’t understand what more you’re wanting.

Not sure what you mean by “normal”. The MAF & MAP sensor readings vary widely, depending on the driving conditions.

What would be a “baseline” for a sensor like that?

The baseline data would be a data point every second for each sensor for the length of the warm up and test drive, maybe 15 minutes. Comes to about 10,000 numbers total for the baseline data-set.

How much are you willing to pay for it? Extra info like this isn’t free.

$200 added to the price of the car seems reasonable. Conceivably this woulnd’t be required for every single car. Car’s with the same configuration should share the same dataset.

No thanks, I’ll pass.
Nothing stopping a new owner from establishing their own baseline if they feel it is worthwhile. But don’t foist that expense on everyone. Frankly, I don’t see any value in it. Anything that is outside the normal allowed tolerance is already being monitored and annunciated by the computers in the car.

They did a baseline on me when I was born. No doctor has ever asked to see it when I’m being treated for some anomaly. BTW- No way I’m ever getting back to that weight or size :wink:


lol … it seems my baseline-data idea is being panned by most everyone here as not useful at all. Ok, I get the message, it appears car owners will have to live with absolutely no baseline data provided to help debug any puzzling future engine symptoms . But I have another engine-monitoring and debugging idea that doesn’t require any baseline measurements except those done by the owner or the owner’s shop.

It is based on a recent podcast puzzler. Their Car Talk shop mechanic has discovered he can quickly tell if an engine has any serious compression problems by just listening to the engine crank; an rr rr rr rr sound means a normal engine. If he hears r rrr rr r rrr r , that means there’s an engine compression problem. This idea could be incorporated into the car’s computer system, then the car would warn you if it noticed a looming compression problem. It could also monitor the battery voltage and current over time during the electrical load of cranking as a way to tell if the battery was starting to go bad or not being fully charged by the alternator.

With all due respect, George, you’re WAY overthinking this

I have to diagnose and repair cars every time I’m at work

It’s called doing my job

Lots of guys before me have figured it out without a “baseline”

And many guys after me will do the same

I and other mechanics are doing just fine

And those that aren’t often get out of the business, one way or the other


This has already been done as well, and it’s not new, maybe 20 years old? It’s called a relative compression test. I can sit in the driver’s seat and crank the engine, and the car will monitor cranking volts and amps and use that information along with rpm and firing order (crankshaft and camshaft sensors) to determine cylinder compression relative to one another. If I see one cylinder substantially lower than the others, then I have identified internal engine failure without even opening the hood.

For vehicles whose onboard diagnostics are not so equipped, I can accomplish the same using a multi-channel lab scope and an amp probe.

You remember those big-box engine analyzers from the 70’s and 80’s? They did that too.


That is called experience George…


I agree with you.

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