20V 4A-GE: Warning Light, Speed Sensor & ECT Diagnosis

[Hook]

If your 20V transplant went into a formerly carb’d car, then it’s likely it came without a Check Engine Light, and then you're like me. A CEL is much more important as a warning and diagnostic tool than most mechanics/electricians give it credit. I recently installed one in my AE101 so here's the how-to if u don't have one, and a problem that my CEL immediately uncovered.

Now to make things clearer, there are two silvertop 20V types, pre-May 1993 and post-May 1993, the 2nd of which comes with OBD II and is much more similar wrt pin designations to the blacktop ECU.On the 20V post-May 1993 S/T ECU, there are 3 plugs, the rightmost of which is the 22pin 'o' plug, this is your concern at this point.
On the pre-May 1993 ECU, the CEL (labelled W) pin is the 5th from the left on the top row, on the post-May 1993 ECU, it's the 7th wire from the left on the top row when looking at the back of the plug as it is connected to the ECU.
The CEL is a negatively-switched output wire, ie. once it's connected to a bulb, the other bulb terminal must be connected to a +ve ignition source. This wire switches from open cct to -ve with the ignition on and back to open cct once the engine has started.

Now, Toyota mass produces their instrument clusters so it's likely you have one already on the dash, just that the bulb and wiring isn't there. Simply get a bulb and socket of the appropriate size and retrofit it into the dash, OR use a 12V LED with the -ve wire connected to the CEL output on the ECU (cuz it's -ve switched). The +ve wire of your CEL must be connected to a +ve ignition source, such as what drives your tach/speedo and can be wired directly into it by using the screw designated IGN+ on either device, and VOILA! You have just installed your CEL.



NOW, on my first test drive I noticed that it lit up upon heavy acceleration and stayed on until I switched off, but lit up again under the same conditions. The ECU was put into diagnostic mode by switching the ignition on with terminals TE1 and E1 connected at the diagnostic port in the engine bay (use a short piece of wire but tin the ends with solder first
to give it strength and prevent frayed strands from touching anything it's not supposed to touch). The CEL flashed four, times, then a short pause and then twice, followed by a long pause and then repeated the same sequence. This told me two things: 1. there was only one error code and 2. that error code was 42, which relates to the vehicle speed sensor.

The vehicle speed sensor needs to be connected to both the speedo (for obvious reasons) AND the ECU as a feedback signal. After 8seconds of driving between 2000rpm to 6000rpm without any VSS signal being detected by the ECU, the CEL switches on to indicate that the ECU is operating in a safe mode and as a result, redline is reduced from 8200rpm to somewhere in the 7000rpm neighbourhood.

The electronic speed sensor on MOST Toyotas have 3 wires, all red in colour with a distinguishing stripe on each.
Red-Blue = +12V (IGN)
Red-Green = earth
Red-Yellow = signal <---There's the wire u want

If you are unsure, switch the ignition on and test the three wires, one will read battery voltage, one will have no potential (earth) and by process of elimination, the other is your signal.

The trick at that point is to simply trace back the wire through the harness (a Multimeter is important here) and connect it to the VSS input, which on the pre-May 1993 ECU is the 9th pin from the left on the top row (labelled SPD) and on the post-May 1993 ECU is the 3rd pin from the left on the top row (labelled SP1).

Once this is done, simply clear the error codes by removing the ECU fuse for about 10-15 seconds. Start the car and let it idle for a couple fan cycles and u good to go.

refer to this thread for links to more 20V info, technical manuals, ECU pinouts and error codes
http://forums.trinituner.com/forums/viewtopic.php?t=125731

[Hook]

for your further enlightenment...and for those who doh care to d/l d whole service manual

Click for full-size.

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[Slow Poke]

damn good info there man

[Aarong420]

Interesting indeed,
Im not sure if i have the pre or post 93 20V. A mechanic told me its
OBD II i have. Also it's the type that kicks in VVT under load, not at 4400 rpm as some say. I know this because i have a LED on the VVT. Some say thats silly and makes no sense but it helps in geting to know your car.

The car works alright you know, i think im not hitin full rpm thou, and i did read it can be because of the same speed sonsor. It's there, and wired to the ECU but i dont have the 101 dash so its not runing to the speedo.
The gradual pick up i was talking about, i think it may be sumthing simple like dirdy injectors, but i cant find a way to take them out and clean them, i tried filling the rail with cleaner and flushing it out with fuel pressure. it worked a lil but not 100%. If its sumthing elce I may need to try your method.
I also believe i am burning on the lean side. This can be because i had to move the tps to bring down my idle.
and with the higher lift cam ill need more fuel. Also with the soon to be 2mm bigger ITB's if they bolt up.


Anyway you said : the 2nd of which comes with OBD II and is much more similar wrt pin designations to the blacktop ECU.On the 20V post-May 1993 S/T ECU, there are 3 plugs, the rightmost of which is the 22pin 'o' plug, this is your concern at this point. :

So i take it im finding that wire, hooking it to a LED light and reading the light patterns?

whats, ( +ve & -ve & cct ) ?

I think i gotta buy a book on this

[Hook]

"+ve" = positive

"-ve" = negative

"cct" = circuit

there's nothing wrong with wiring up a "VEEETEK YO!" light on your 20valver...I have one installed too

if your VVT kicks in independent of rpm then likely it's the post-May1993 ones like mine...just find the pin, connect it to the -ve wire of an LED and connect the LED +ve to a +ve ignition source

I'll post more on code reading 2mro

[Aarong420]

Someone told me that my ecu will not save the codes to be read on the diagnostic tester and because of this i cant use it to find problems.
If I where to connect the Engine Check Light would this solve the problem?

[Hook]

remember, the "W" connector on the ECU is a negative-switched output.so connect one end of your warning light (or negative lead on your LED) to this and connect the other warning light lead to a positive ignition source

I tapped an ignition source from the "IG+" lead on my tach (it's written on the back of the instrument cluster) and ran a thin single core wire back to the ECU "W" connector

[corollalover101]

good info here

[Aarong420]

So i went to get this warning light hooked up today, and i realise there is no 22 pin connector, theres a 26 pin connector a 16 pin and a 12 i think.
but in the case of the 26 pin, which wire would it be?
The 7'th wire from the left is a red wire with a black stripe. is this not for the VVT?

[Hook]

hmmm...12pin u say?

then THIS may be what u're looking for

[Aarong420]

its downloading but doesnt work.

[Hook]

nope...works fine...I clicked the link on 3 different computers since and it works fine

just google "4age 20V silvertop pinouts" and u'll get it

[Hook]

we learn new things every day folks...I recently had a problem with my "O/D Off" light flashing on my dash..here's the remedy

[Aarong420]

yo man, i got the GT dash wired up over the weekend so i have everything proper, engine light comes on, but when i tested it, ..." i pulled out the speed sensor connector " to see if i got any codes, but the engine light blinked normal ?..i drove the car with it diss con, for a while b4.

[Aarong420]

also the tach reads me bouncing tach at 7 sumthin, not 8200....so im confused

[Aarong420]

I dissconnected the TPS plug and found the engine check light to be working correctly. But why when I drive the car and the engine light comes on, it doesnt save the code to be read afterwards.

[Hook]

waay..I now seeing this question

it prolly needs to be driven in test mode to pick it up..there's a write-up on it in the BT service manual in the diagnostic section

apparently some faults don't trigger the CEL immediately but are either stored, or the car needs to be driven in testmode to pick it up...dunno why they did it like that

[Dave-ve]

does anyone know of any diagnostic software that works with the asian market toyotas? almost all that I've found so far are only guarenteed to work on the US market cars.