Can the ECU get a fault wrong?

[JustCallMeOrlando]

Hey all,

Just thought I'd pick peoples brains about a strange phenomenon that's happened since my car got its brain transplant.

Before with my old ECU, I could drive around all day pretty much, and not get any codes, unless I went on the freeway, where as soon as I sat for a about 10 seconds on 100kph my CEL would come on, and later investigation would show that it was the speed sensor code, this being because I hadn't wired the speed sensor input to the ECU. If you dropped your speed, the CEL would go off, and it'd come on and off going down the freeway.

Now since I wired in the Gen3 ECU with its similarly disconnected speed sensor wire, we have a similar pattern, but with a strange twist. First off, the CEL doesn't go off until you stop the car. Secondly...it doesn't throw the speed sensor code at all.

It throws code 31 which is to do with the AFM. The exact same conditions which caused the old ECU to register a speed sensor code now throw this, it's as if the ECU has the codes confused...is this possible?

Cheers,
Nathan

[ViPeR_NiPPleX]

hmm good question that, is it possible the gen3 codes don't equal gen2 codes?... i'd hope not

[The Witzl]

have you reset the ECU fault code memory each time you check the codes?

.... reset memory by disconnecting the battery for around 5 minutes.

[ra23celica]

Silly question here, but do the pin-out's differ between ECU Gen's and has your re-wiring taken this into account?
My next move would be to start taking out all the other sensor's one by one and testing each one of those to see if the ECU throws the expected fault code for that sensor.

[JustCallMeOrlando]

Yep, ECU has been reset and cleared each time. If I drive around normally it doesn't happen, if I thrash the bejesus out of it it doesn't come on. If I cruise around at 2000rpm it doesn't come on. It only comes on under the same conditions as the old speed sensor code.

The only thing I can think of is that it may be different codes, but I haven't seen separate ones for the Gen3. The boost cut code is the same

The rewiring was an entirely new loom, with new plugs for the external wires, and everything is wired correctly, I double-checked if before I installed it.

[ra23celica]

I have found new codes between Gen1 and Gen 3 1G-GZE ECU's so its not beyond the realm of possibility. I think at least one new code got added later in the GZE's life.

[o_man_ra23]

Unless there is a fault with the ECU's wiring, EEPROM or MC firmware, then it wont throw a wrong code. Generally, the EEPROM, internal wiring and MC firmware would be untouched, unless the ECU has been re-programmed by somebody else. So, i would say its running a different set of fault codes if your wiring is as correct as you say. Why did you disconnect the speed sensor?? was it to remove a speed limiter?? If so, i would say reconnect the speed sensor and get a piggyback speed limiter remover.

Cheers, Owen

[JustCallMeOrlando]

The speed sensor was never connected because 1) I couldn't be arsed tracing and wiring it up, 2) I don't need a speed limiter, and 3) the ECU doesn't really give a rats about the speed sensor wiring unless you have an auto box for it to control.

So thus far, it appears the only possible solution is the Gen3 has a slightly different set of codes, and it holds the CEL light on for the entire time, unlike the Gen2 which deems it as minor.

[JustCallMeOrlando]

The ECU is an auto one as well, which could prove a difference as to why the ECU thinks it's worth keeping the light on.

[ndgcpr]

i have an auto ecu in my car also. I was having the same code type thing happening (yes i have a gen 2 so all of this is probably useless) until i got off my butt and wired it, it should be pink . Anyway the speed sensor code from memory has nothing to do with speed, it comes on if the revs are over 3G for more the 2 seconds with the speed sensor slower then 10 KPH or something, so as a test i would cruise in a low gear above 3G for a while and see if it comes on, it should atleast eliminate wheather is is because of the speed sensor or not.

what is the actual definition of the AFM error?

[CrUZida]

AFAIK Toyota have never changed the number of a code.
Sure some ecu's have new codes, other ecu's drop unneeded codes, but code 11 on one ecu is code 11 on every other ecu.

At least in my experience for 5MGE vs 1GGTE vs 7MGE vs 1UZFE vs 2JZGTE

[o_man_ra23]

I would say there probably isnt much of a speed limiter on it anyways, nothing that your likely to get to in every day motoring anyways, so wire it up with a switch, so that in normal driving its hooked up, and when you wanna go fast, just flick the switch to d/c the speed sensor, and ignore the CEL.

Cheers, Owen

[ira11y]

Not that i know a lot about this particualr ECU but heres a theory...

You could be correct that the speed sensor is causing the problem, the fault code may not give you the exact diagnosis as you percieve it but think of it in terms of a processor.

the processor is expecting a signal in from the speed sensor, or perhaps if its auto the speed sensor sig goes to the box and the box sends a sig back to the ecu for controls. the ECU registers a problem processing some part of its expected program due to lack of signal, this stops the ecu from doing what it thinks is normal, therefore it sees it as an ECU fault.

Ok its a long shot but you never know.

[o_man_ra23]

nah ira11y, the ecu is pre-programmed to give off a certain fault code for a certain fault condition. each sensor has an expected range of values which it should give for certain conditions. If a sensor is faulty (ie not giving a pwm signal for speed), then it looks at the other sensors to see how many of them are correct with respect to each other... ie the afm is open a certain amount, there is a certain number of revs, the water and air temps are both registering in the allowable range, the oxy sensor is within limits, etc, etc, then it says, well they cant all be wrong, so the most obvious problem is the speed sensor. If there are 2 faulty sensors which work together, then an obscure error can occur.

Cheers, Owen.

[brett_celicacoupe]

i was getting a code 16 on my gen3 1ggte for a while. i noticed that it was while i had tempory, dodgey, flexible hose linking the IC pipes - not sure if there was any link.

still to date i am unsure what that code was for