Need Help from Electrical Gurus (1 Viewer)

[SmokingRocks]

I'm assuming you posted your last post and hadn't seen my revised diagram? @sbman

 

[sbman]

Yes we cross posted. Your latest diagram looks reasonable. It's no fun to work blind though, a scope is really worth it for these kinds of projects. The Rigol scopes are around $300 for a two channel and then you know for sure what you are working with.

 

[TrickyT]

The resistor in series with the collector lead of the combo meter output transistor is 10 ohms, not 68. It's the one circled in this image:

The "100" means 10 x 10**0 = 10 x 1 = 10 ohms. Also, the resistor you show on the base lead of the same transistor in your circuit, 10 ohms, is pretty low and may lead to destruction of the transistor. A value of 1K or even 10K is more typical. Don't forget that the transistor has a forward gain of usually 100 or more, so it doesn't take much current to drive it.

Maybe both ECUs will be happy with just the buffered output of the VSS like your circuit shows, although in the OE configuration there looks to be a fair amount of additional circuitry to transform the "shape" of the VSS waveform to something different for the ECUs..

 

[Pin_Head]

I threw away a Tek 555 O scope because nobody wanted it for cheap or free. I have a smaller one now.

 

[TrickyT]

I threw away a Tek 555 O scope because nobody wanted it for cheap or free. I have a smaller one now.

Dang, I would have jumped at that in a second. But it's pretty amazing what you can get for your money now a days. I bought a JYE DSO 112A a couple of years back for ~$60. (Still available on Amazon.) It's got a touch panel and color display, with Vmax of 50v peak. Certainly not as powerful as a Rigol, but for $60 hard to go wrong.

 

[landcrshr]

Also, the resistor you show on the base lead of the same transistor in your circuit, 10 ohms, is pretty low and may lead to destruction of the transistor.

This is the challenge, switching the transistor fully on ("saturating" it) without burning it up. We don't know the resistance of the VSS circuit, so how do we select the base resistor? We'd have to make the circuit more complex to isolate it from the unknown.

 

[landcrshr]

BTW, this shows the collector of the transistor grounded and that looks like a MISTAKE. I point this out because you copied it into your simulator that way, but no matter really since you're not touching that part.

 

[SmokingRocks]

no dice.

 

[SmokingRocks]

Well I figured it out... and the solution is so simple I literally smacked my head.

So the trick is to just throw away the speedo board. It works just fine if you completely bypass it.


All of this concern about conditioning the signal for the ecu's should have been disregarded as soon as I saw the diodes in each of the ECU's. As @landcrshr pointed out the signal the ecu's are lookin for is a ground which happens between pulses at the VSS's transistor.

I stuck my multi-meter on the line from the VSS (+) and ground (-) then tested AC voltage while rolling slowly then at speed. I got a max value of 7.8 volts, so thats coming from the ECU's (a bit higher than what they say but whatever). Then I set the meter to check resistance between the VSS signal to the speedo and the ground (-), while rolling slowly. I was able to see that I had 140 Ohms resistance at the peak.

So then I test drove it. Cruise control functions fine, ECU has not thrown any codes. Might just be that simple. Jesus I tortured myself over this, I can only laugh at myself now. Atleast I learned a lot more about what once was my least understood and often feared subjects.

Thanks for the help everyone!

 

[SmokingRocks]

So the only thing that I could imagine the speedo board did was possibly to 'condition' the signal so that it had equal time on and off.

If so then the current set up will eventually cause a code or issue since the pulse is very short as seen in the green line on the scope here:

Solution would be to install a voltage regulator to take 12 volts down to 5 then pin it to the negative side of an op-amp with a max ouput of 3volts. Which changes the pulses to be more uniform as seen here in blue.

 

[SmokingRocks]

built an oscilloscope for my ipad tonight. Checked the signal and it looks nice n square.

 

[Jimmyrios]

Hi everyone...I have read with a lot of expectation this thread in special...so interesting...to me...As I am having such dificult issues with my own lc80 speedometer not working for such a long time, really a headache...also the same problem with the cruise ecu not reciving signal, as it show with the autodiagnose code 21 of the ccu, and the automatic transmition not doing shifting correctly even sliping gears....the speedometer needle begings working suddenly only when you revolution the engine way too much, like if it would recive energy only in those condition...could it be something related to a transistor or a bad signal that comes from the vss...a resistance...etc. I really apreciate some clues and guidance

 

[SmokingRocks]

If the speedometer is not working and the ecu isn't getting the VSS signal then the issue is your VSS 1 or VSS 2 sender units or the electrical pathways.

The speedometer can be broken and the ECU will still see the VSS signal ONLY IF the VSS are actually sending a signal. Download your FSM from the link in my signature so you can follow the electrical wiring diagram to troubleshoot.

 

[Jimmyrios]

If the speedometer is not working and the ecu isn't getting the VSS signal then the issue is your VSS 1 or VSS 2 sender units or the electrical pathways.

The speedometer can be broken and the ECU will still see the VSS signal ONLY IF the VSS are actually sending a signal. Download your FSM from the link in my signature so you can follow the electrical wiring diagram to troubleshoot.

Thank you SmokingRocks for your proper reply...well...following your instructions...made an electronic guy check the speedo circuit and found a cut off cable that leads to the speedometer needle coil...the speedometer begun to work again all right, but there is a fail code leading to the cruise.control ecu says no speed sensor signal...there is a black/red cable that seems to deliver some kinda of signal from the speedometer to the cruise computer, the tcm and de ecu, and again seems there is the problem, no signal or maybe as in your diagram, could it be some kind of problem realted with the ccu ecu and that diode in the computer that is blocking the signal...???

 

[sbman]

Thank you SmokingRocks for your proper reply...well...following your instructions...made an electronic guy check the speedo circuit and found a cut off cable that leads to the speedometer needle coil...the speedometer begun to work again all right, but there is a fail code leading to the cruise.control ecu says no speed sensor signal...there is a black/red cable that seems to deliver some kinda of signal from the speedometer to the cruise computer, the tcm and de ecu, and again seems there is the problem, no signal or maybe as in your diagram, could it be some kind of problem realted with the ccu ecu and that diode in the computer that is blocking the signal...???

How are you reading a code from the cruise control ECU? I am not aware of that ECU having any function to do so, there is no data connection there to read from.

I am guessing the code is from your engine ECU and saying no speed sensor signal. You need an oscilloscope to see the speed signal and verify that it is present. It is a square wave signal proportional to speed. The speed sensor drives the speedometer, and the speedometer drives a transistor that generates the speed signal for the engine ECU, cruise control ECU and diff lock ECU. The wire color you mention don't make sense, the Black/Red wire should be for the park/neutral switch, but I guess you haven't said what year or specific model of 80 series that you have. What year is your 80 series? Is this a U.S. model or a world model? (does it have OBD-II?)

 

[SNLC]

How are you reading a code from the cruise control ECU? I am not aware of that ECU having any function to do so, there is no data connection there to read from.

I am guessing the code is from your engine ECU and saying no speed sensor signal. You need an oscilloscope to see the speed signal and verify that it is present. It is a square wave signal proportional to speed. The speed sensor drives the speedometer, and the speedometer drives a transistor that generates the speed signal for the engine ECU, cruise control ECU and diff lock ECU. The wire color you mention don't make sense, the Black/Red wire should be for the park/neutral switch, but I guess you haven't said what year or specific model of 80 series that you have. What year is your 80 series? Is this a U.S. model or a world model? (does it have OBD-II?)

Just an FYI, CC light flashes for its specific codes. When there is an issue the indicator light will flash just like OBD1, count the flashes and refer to the FSM for those specific codes.

Cheers

 

[sbman]

Just an FYI, CC light flashes for its specific codes. When there is an issue the indicator light will flash just like OBD1, count the flashes and refer to the FSM for those specific codes.

Cheers

Thanks! The EWD makes no mention of that, I'll have to visit the FSM for those details, hadn't looked there.

 

[SmokingRocks]

Yes it does. Take a look at my complete fsm for 93-94. It’s very well detailed

 

[Jimmyrios]

Yes indeed, haven specified about my rig, its a fzj80 93, obd1, in the guiding material I have, says to make a bridge in the link connector, so the cruise control ecu begins to send codes, in my case is DTC 21, pointing towards that there isnt a signal from the Vss 1. As I said previously, I manage to find the problem with the speedometer needle not working, changed 2 capacitors, another blue one also, checked resistances, and finally the problem lied on one of the speedometer coils that makes the needle move was cut off, dont know why....that was the reason the needle only began working when I revolutioned the engine way to much, now it works properly....still there is a DTC 21 code present meaning a lost signal for the cruise control and it does not work. And yes the speedometer should send a square signal to the ecus by a Red/black cable on this 93 model...seems to my there is some kind of missing ground, dont know anymore where to begin checking...any clues...!!! There is no check engine lighting and the lockers are fine, but what worries me most is that the shifting in the automatic transmition its bad even sometimes slipping, for what I read can damage the costly electronic transmition components, so the LC remains parked for more than 5 years unable to find the solution to this car. Thank you for your concerns. SmokingRocks, where can I take a look at your fsm 93-94 material? Thank you

 

[SmokingRocks]

... DTC 21, pointing towards that there isnt a signal from the Vss 1. As I said previously, I manage to find the problem with the speedometer needle not working, changed 2 capacitors, another blue one also, checked resistances, and finally the problem lied on one of the speedometer coils that makes the needle move was cut off, dont know why....that was the reason the needle only began working when I revolutioned the engine way to much, now it works properly....

First of all, Bravo! For displaying a serious knowledge of the electronics systems used in our vehicles as well as being able to repair them. 99% of people that have this problem usually buy a second hand functioning gauge cluster. Nicely done.

...still there is a DTC 21 code present meaning a lost signal for the cruise control and it does not work. And yes the speedometer should send a square signal to the ecus by a Red/black cable on this 93 model...seems to my there is some kind of missing ground, dont know anymore where to begin checking...any clues...!!! There is no check engine lighting and the lockers are fine, but what worries me most is that the shifting in the automatic transmition its bad even sometimes slipping, for what I read can damage the costly electronic transmition components, so the LC remains parked for more than 5 years unable to find the solution to this car. Thank you for your concerns. SmokingRocks, where can I take a look at your fsm 93-94 material? Thank you

Without a VSS signal, the transmission ECU runs off of a different shift program, kinda like a limp home mode. Its sloppy, shifts at odd times and can seem slippy, I do wonder if this was by design from Mr. T so that the drivers would be motivated to figure the issue out fast.

So onward with that;

Have you checked the VSS input port on the Cruise ECU to verify that it is seeing the sinewave when the VSS is turned and the speedometer is showing speed?

If there is no sinewave at the CC ECU then you need to trace that circuit back to figure out where it's broken. The speedometer does not send anything to the cruise control ecu, rather they both are receiving the same signal on the same circuit, so your issue is likely a broken pathway.