Jumping Tach and Speedo Needles

[Shel_B]

I've been watching a few auto repair videos on YouTube, such as Rainman Ray, where the gauge cluster is shown on engine startup. When starting the car, the speedometer and tachometer needles swing out to their full-scale max values for about a second and then behave normally afterward. I've seen this on just about all brands of newer cars so I'm assuming it's normal. What causes that behavior?

 

[DriveHard]

calibration - going to the extents of motion, logging those values, then resuming operation with the new extents limiting motion and resolution.

 

[Shel_B]

calibration - going to the extents of motion, logging those values, then resuming operation with the new extents limiting motion and resolution.

Is this just for digital gauges? I don't see it on older cars, such as my Camry or friends' cars.

 

[DriveHard]

Is this just for digital gauges? I don't see it on older cars, such as my Camry or friends' cars.

Any gauge that is computer controlled falls into this. Even my "newer" Buick does it.

 

[PimTac]

Any gauge that is computer controlled falls into this. Even my "newer" Buick does it.

Yep. Even the headlights on some vehicles go through a similar exercise.

 

[dishdude]

It's just for show, a little eye candy at startup.

 

[Escape08]

It's just for show, a little eye candy at startup.

That's what I thought too

 

[JohnnyG]

It's actually programmed in, and serves no useful purpose. Long ago (and far away) '99 something era caddys would do the needle sweep thing. Somebody decided to get rid of that "action" and customers got upset. GM soon implemented that again, believe it or not!
Like Dishdude says, eye candy.

Noow, if you have an old tach/speedo with a cable, there are many things that can go wrong. In fact there are places that will completely restore not just the inner working, but dial faces and needles as well.

 

[mk378]

It is a self test to show that the motors that move the gauge pointers can move through their full range without getting stuck. On certain clusters, motor failure was common. If your speedometer is prone to go up to 58 then stay there no matter how fast the car is going, you would want to know that before driving.

 

[DriveHard]

It's just for show, a little eye candy at startup.

While I can't comment specifically on the needles in a display for an automobile, I can confirm the sweep is to calibrate and check for proper operation at startup for off highway vehicles - not for "eye candy".

 

[KrisZ]

It absolutely is for eye candy. Now, for some applications, like racing, heavy equipment etc. it’s a good visual confirmation for the operator that the gauges are working, but it is not any sort of calibration or anything like that. Could be also a “self test” but you highly doubt a simple gauge circuit has needle limit sensors.

Calibration values are permanently stored and only need redone when components are replaced and that is a separate procedure not baked into normal operation.

Edit:
Just occurred to me that the servo itself could report its position back to the controller, so it can test itself without needing other sensors, but that is not calibration.

Calibration is something totally different and requires a known good value to compare to, therefore a servo cannot calibrate itself.

 

[dishdude]

While I can't comment specifically on the needles in a display for an automobile, I can confirm the sweep is to calibrate and check for proper operation at startup for off highway vehicles - not for "eye candy".

The Integra in my signature has a full LCD IC and does a gauge sweep at start up...that's eye candy....there are no stepper motors to calibrate.

 

[Tomioka]

It's a heavy truck thing that goes way back. We've got dinosaur International trucks that perform a full gauge sweep at key on.

Then the gauges don't work later on.

 

[Blinker]

Many school buses have done the gauge sweep thing since the early 2000’s, I think even sooner than that. Some 1990’s Chrysler vehicles have a gauge reset procedure which causes the gauge cluster to go through a reset/test phase and the gauges do an incremental sweep.

My opinion is the gauge sweep is a gauge check.

 

[Blinker]

It's a heavy truck thing that goes way back. We've got dinosaur International trucks that perform a full gauge sweep at key on.

Then the gauges don't work later on.

This tells me that the instrument panel gauge works, but something is wrong with the circuit that feeds the gauge.

 

[DwightFrye]

On my Nissan 370Z it most certainly was for "eye candy". There was a setting in the driver preference menu where you could turn the feature on or off. I switched it off after the novelty wore off. Which was about the second day.

 

[dishdude]

My new Integra that has a full LCD screen for the gauges does the gauge sweep at startup as the system boots. Obviously this is only done for visual effect and eye candy, there are no stepper motors.

 

[zzyzzx]

It's just for show, a little eye candy at startup.

I was also thinking that this was something from the marketing department.

I wonder of ForScan can turn this off?

 

[D60]

My '11 SuperDuty does this, I figured it's both eye candy but also tells you if the needles can sweep when commanded to...so also a self-test.

It's essentially the same reason all your idiot lights come on for the first few seconds: self test.

 

[1 SX]

I have a client that has an old probably mid 2000s Dodge Caravan type Chrysler product and the battery was dead. I jumped it and I saw that needle sweep action and thought something blew in the cluster. It looks so out of place in an old minivan lol.

I've only owned one or two vehicles with the needle sweep - cool... kinda, necessary not really.