Effects of no SPD signal to ECU?

[Drifty Midship]

I have a busted speedo.
This is generating an error code 42 which is No SPD signal...
From the other thread on speed sensors running ATM I guess a pulse signal in my AW11 comes from the back of the speedo cluster also. Though I havent experienced any rev cut.
Wondering if anyone knows what DOES the ECU ACTUALLY DO WITH the SPD SIGNAL?
How does the ECU not recieving this signal actually affect the running?
confused

Cheers

[Cool1]

If its anything like the 3S, It wont matter a dam bit.

[stradlater]

ECU's don't tend to be affected by speed sensors, despite the fact that they measure it.

Not that I'm specifically sure, I think things like traction control and Auto gear selection(maybe) might use a speed sensor.

It won't rev cut on a lack of speed sensor, nor would it varying fuel or ignition timing given that they are load related, NOT speed related.

An example being: My Haltech IG5 has a speed sensor input. No despite the fact that it only controls ignition, this speed sensor seems to do nothing other than show up on the engine diag screen.

[JustCallMeOrlando]

The ECU uses the speed sensor for a couple of things, knowing when to signal the speed limiter, and for controlling an auto. My car hasn't had the speed sensor hooked up ever, and constantly throws the speed sensor code whenever I drive on the freeway. Doesn't affect how it drives though.

[The Witzl]

There actually ARE some effects to engine operation with a factory Toyota ECU if you dont have an SPD signal sent to the ECU.
However, these may not be apparent in your engine.....

The most common engines where you might notice this is:
4A-GE smallport, 4A-GE 20V, most any post 1989 engine w/automatic box, most any engine that revs above 7200rpm.


What happens is in these engines (excluding the operation of autos here) is that the ECU lowers the rev limiter to 7200rpm and [this is yet to be confirmed] modifies the igntion timing - the ECU thinks you are 'free-revving' the car.

4A-GE 20v engines is where this is most obvious....

[72 TA22]

With my Gen3 GTFour 3SGTE without the SPD signal to the ECU.

1. The engine light came on when the engine run under load (Error code 42)
2. Would only boost to 0.6 bar (now boosts to 0.95bar after SPD connection made)

Other than these two observations the engine seemed to run fine.

[CrUZida]

I've heard people claiming that engine braking has improved after hooking up SPD

[urantia]

Also things like the progressive power steering won't work properly without the speed sensor wired up.

[CrUZida]

Every PPS system I've looked at has had its own ECU

[urantia]

Don't know about all of them, but with the jza70 PPS ECU, it needs to get an SPD signal to function correctly.

[CrUZida]

Must be a 1JZ thing then (I think maybe the JZZ30 is the same?)
But the MA70 definately has its own ECU.

[-GT-]

I don't have the speed signal connected to my 20V (to disable speed cut - but haven't actually got it that far up yet to benefit though... ) but i can tell you it definately doesn't rev limit at 7200, pulls all the way to 7800.

Would it advance or retard the ignition timing thinking it is free revving? Would i notice in the power delivery or something, how can i check if its doing this?

[urantia]

Must be a 1JZ thing then (I think maybe the JZZ30 is the same?)
But the MA70 definately has its own ECU.

I'd of thought it was the same for the MA70 too.
Yeah the 1jz has it's own PPS ECU aswell, but it needs the speed sensor wire hooked up to it so it can disengage the PS at about 65km/h or there abouts. I'm not sure how the MA70 one works as my ma70 didn't come with PPS, surely it'd be the same tho, and requires the spd signal?

[Joshstix]

The speed sensor is also used to help with bringing the engine back to idle quickly and smoothly when stopping the car. With my 3S without the speed signal it would idle at ~200rpm for 6-10 seconds when coming to a stop rather than going straight back down to idle speed.

[Norbie]

Hmmm, sounds like it might be worthwhile hooking up my speed sensor one of these days.

Has anyone successfully done this in conjunction with an old-style speedo cable? I've heard there are adaptors that allow you to run both at the same time, but never actually seen one.