Gauges In Cluster

[SpikedCola]

How are the gauges in the cluster controlled? For example, to make the speedo show 100km/h. Is it given a certain voltage? What does this voltage range from and to? Im guessing 0v - 5v? Is it the same voltage for the tach? If it works out, Ill have an interesting mod to share soon :)

PS. One last thing. Turning the car over. If you hold the key for three seconds, but the car starts in two (ie, holding the key for a second after its started) will it cause any damage? If not, another mod :)

EDIT: one more question: is there a wire or something in the ECU or otherwise that goes high when the car is running, but is low when the key is first turned to run (ie is only on when the engine is running, not just based off the key).

[SpikedCola]

Bump. Maybe this would be better suited in electrical? Though not many people visit that section.

[blkcelica01]

the only person who can help you is 2-way

[pnoy]

How are the gauges in the cluster controlled? For example, to make the speedo show 100km/h. Is it given a certain voltage? What does this voltage range from and to? Im guessing 0v - 5v? Is it the same voltage for the tach? If it works out, Ill have an interesting mod to share soon :)

PS. One last thing. Turning the car over. If you hold the key for three seconds, but the car starts in two (ie, holding the key for a second after its started) will it cause any damage? If not, another mod :)

EDIT: one more question: is there a wire or something in the ECU or otherwise that goes high when the car is running, but is low when the key is first turned to run (ie is only on when the engine is running, not just based off the key).


planning on a digital tach huh?

[S|Lv3rBu||et]

I can tell you it is bad to hold the key in the start position for any amount of time once the car is started. You'll fry your starter... that's bad.

[Blue Bomber]

The speedo is controlled by the speed sensor, which sends signals when it's turned by the transmission. The tach is controlled by the signals from ECU and igniter. From what I've read, it doesn't seem like there's a varying signal for either tach or speedo, only pulses. More info in Repair Manual Vol 1 page DI-114 and Vol 2 pages BE-5 and BE-39.

[SpikedCola]

planning on a digital tach huh?
Nope, guess again :)

I can tell you it is bad to hold the key in the start position for any amount of time once the car is started. You'll fry your starter... that's bad.
Guess I've gotta start looking for signals then.

The speedo is controlled by the speed sensor, which sends signals when it's turned by the transmission. The tach is controlled by the signals from ECU and igniter. From what I've read, it doesn't seem like there's a varying signal for either tach or speedo, only pulses. More info in Repair Manual Vol 1 page DI-114 and Vol 2 pages BE-5 and BE-39.
Oh boy, PWM! Thanks for the references.

[Boosted2.0]

How are the gauges in the cluster controlled? For example, to make the speedo show 100km/h. Is it given a certain voltage? What does this voltage range from and to? Im guessing 0v - 5v? Is it the same voltage for the tach? If it works out, Ill have an interesting mod to share soon :)

PS. One last thing. Turning the car over. If you hold the key for three seconds, but the car starts in two (ie, holding the key for a second after its started) will it cause any damage? If not, another mod :)

EDIT: one more question: is there a wire or something in the ECU or otherwise that goes high when the car is running, but is low when the key is first turned to run (ie is only on when the engine is running, not just based off the key).


Most of the gauges are controlled by stepper motors or the LEDs which are all controlled by a microprocessor built into the combo meter. It communicates with the ECU over a proprietary data bus (LAN). Unfortunately the interpretation of what data bits mean what is not information that Toyota has made available, which is why AEM gave up on making an EMS for the Celica - they didn't want to go piggyback and they couldn't figure out how to control the gauges.

[SpikedCola]

Damn. There goes the gauge sweep idea. Thanks for the info, boosted. Ohwell, at least project #2 is still on track :)

[SpikedCola]

EDIT: one more question: is there a wire or something in the ECU or otherwise that goes high when the car is running, but is low when the key is first turned to run (ie is only on when the engine is running, not just based off the key).
Or even the other way around... bump?

[SpikedCola]

Still curious about #2

[Celica402GTS]

pm dooly

[SpikedCola]

Dooly would know if there is a signal that goes high / low when the car is started (not cranking - actually started)? Seems like a 2way kinda thing.

[Kore971]

Damn. There goes the gauge sweep idea. Thanks for the info, boosted. Ohwell, at least project #2 is still on track :)


don't give up on that..., just go find a gauge assembly from a scion TC, they do the guage sweep.., i'm sure its just something in there that controls it..., i would like to see it done on a celica..

[SpikedCola]

The idea was to interrupt the signal either from the ecu to the gauge, or from the sensors to the ecu, override them with a signal that will make the gauges go from zero to full and back, then re-enable the original lines. It wouldnt be hard to do, I just need to know how the gauges operate.

Once I start college in the fall, Ill have access to a scope, among other things, so once I get the lines pinpointed I might have a better shot at it.