Replacing my battery made me wonder if any of my gauges actually worked. Obviously the fuel gauge works (maybe a little too well...), but what about temp gauge, the oil pressure gauge, or heck even the battery gauge. Which brings something to mind, what exactly does the battery gauge even measure? Does anyone even use the oil pressure gauge?

So I'm wondering how would I check to see if these gauges did their jobs, or on a modern car do they even do anything?

 

Our gauges are no longer calibrated, so are just meant to be used as monitoring devices, so no, they don't actually "do", or control anything, they just generaly monitor the range of the systems they're connected to.

The "battery gauge" is an uncalibrated volt meter, that measures the alternator & battery voltage range.

The uncalibrated temp gauge monitors the engines coolant temperature range, but the computer has it's own temp sensor, thats seperate from the one that opeates the dash tamp gauge.
The computers temp sensors reading in degrees can be read with a scantool, as can the vehicles voltage.

Ford has also messed with our oil pressure gauge, such that it's no longer much more than a mechanical idiot light.
Our oil pressure gauge is electrically controlled by a pressure switch, which closes to ground the gauge & it's electrically trimmed to read mid scale, when we have about 7-11 psi oil pressure.

To read real oil pressure, we would have to connect, or "T" in a mechanical gauge, or an electrical variable resistor pressure sending unit, at the oil pressure switch location.

The fuel gauge, speed-o & tach, do provide some meaningful info though.

Auto manufacturers got away from gauges that provide actual numbers, because customers became so uneducated about how to read them, that their service dept's became indundated with nonexistent complaints, from folks that never learned how to properly read a danged gauge.

So now we're stuck with idiot lights & idiot gauges!!!! lol

 

I almost want them removed from the gauge cluster then.

Something in me keeps wanting to look at them and expect them to tell me something meaningful - like "Battery is undercharging" or "you're a quart low on oil - oil pressure is lower" But I guess it doesn't work like that anyway.

Shame, I'd actually be pleased if the next year of vehicles allowed the driver direct access to the ECU so that he could display the real values being used by the computer on a secondary instrument cluster.

 

Our gauges aren't useless, they are just less precise than they used to be. The gauges are marked with High, Low, Normal, ect, so if they are indicating out of range, or trending different, we know something needs attention, or is wrong, but not by exactally how much.

We should raise the hood & check our fluids on every gas up, so thats what "dipsticks" & see through reservoirs are for, but if most folks never look at the dash, why would we expect them to pull the hood to check fluid levels????

If occasionally looking at the dash, or pulling the hood to check fluids is too much to expect of the operator, then the mfgr gives us warning lights, chimes & buzzers, to get our attention & yes some vehicles are wired to display low fluid levels, like crankcase lube, brake fluid, coolant level, ect.

For example if our brake warning light is on while we're driving, it can mean low fluid level in the brake master cylinder. Or if our "Check Gauge" light is lit, the computer has sensed some out of parameter situation & is trying to call our attention to it on the dash, so we do have some help in knowing when something has gone wrong that needs our atention.

Additionally, we do have access to the computer PID's, through the DLC, located under dash right between our legs. So we could hook up a scantool & monitor all sorts of things not normally displayed on the dash instrumentation.

BUT, if most folks never look at the dash, or if they did, can't intrepret a gauge, loading them up with even more instrumentation, or data displays would likely be a counter productive, costly & an aggravating thing service shop wise, for the mfgr to do, as folks would be in there for every little glitch they happend to see. Rememeber why Ford turned our oil pressure gauge into a non changing, on/off idiot gauge!!!!

But we gauge lovers can install gauge sets, to monitor just about any parameter we would desire, or we can access the computer through the DLC & have it's PID's displayed on a screen of our choice, but now there is so much data available, we could go into data display over load & not be keeping our minds on our driving, hands on the wheel & eyes on the road!!!!! lol

 

I don't know if you are aware but there is a device which will let you read the ECU.
ScanGaugeII - Trip Computers + Digital Gauges + Scan Tool