Ok...I found the material its great...well, for what the diagram of the paths of signal posted previously by SmokingRocks, I belive my trouble seems to be that the vss 1 or the circuit in the speedometer, not sure, its not doing FOR SOME REASON the alternative drop to - 12 volts leading that the signal from the control modules ecu ccu and tcm can complete with the ground its circuit. The circuit remains blocking with the + 12volts from the sensor the signal coming from the ecus...to the ground. What could be the cause..or wich electronic component be the one responsible. ? I though even the integrates in the speedometer could be damaged?
Need Help from Electrical Gurus
- Thread starter SmokingRocks
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- #82
see my previous post.
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- #84
if you are getting any SQUARE WAVE to the cruise control ECU and it's still throwing this code then the issue is either a broken or corroded pin on the plug or the input terminal of the CC ECU. I'd check, clean, reassemble and test again.
If the problem persists then you'll need to figure out a way to verify that the signal is getting all the way to the correct pin of the CC ECU, if you can verify that then it likely points to a faulty cruise control ECU.
Side note: All of the Land Cruiser ECUs are very simple, based on IF/THEN logic switching boards. This isn't a 2023 Mercedes with CANBUS. The CC ECU does not care about anything other than just seeing a SQUARE WAVE, it has no way of knowing if the SQUARE WAVE is in or out of phase with what the speedometer sees. (And it wouldn't matter anyway because both are seeing the same wave because they are in a parallel circuit with the VSS.
If the problem persists then you'll need to figure out a way to verify that the signal is getting all the way to the correct pin of the CC ECU, if you can verify that then it likely points to a faulty cruise control ECU.
Side note: All of the Land Cruiser ECUs are very simple, based on IF/THEN logic switching boards. This isn't a 2023 Mercedes with CANBUS. The CC ECU does not care about anything other than just seeing a SQUARE WAVE, it has no way of knowing if the SQUARE WAVE is in or out of phase with what the speedometer sees. (And it wouldn't matter anyway because both are seeing the same wave because they are in a parallel circuit with the VSS.
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Ok thank you...I ll verify everything you said and post back the results.... I agree there might be some pathway problems
Ok...sure...great clues again SmokingRocks...I ll recheck everything and get back with the results...thanks again
It makes sense that the mechanical needle and coil drive portion of the speedometer has nothing to do with the VSS output to the ECU/TCU/CC, but it sounds to me like someone clipped the wire going to the speedo coil to try to fix something. Perhaps the VSS signal from the sensor is weak and having the speedo coil hooked up is eating up what little signal is there. These kinds of questions are best answered with an O-Scope. They are fairly cheap these days. I'd start by checking the R/G wire on the combination meter for the sine wave (speedo sensor spinning), then check for the VSS signal output on the B/R wire to see if you are getting the square wave output there. If not, depin it and check again to see if something external is shorting the signal. @Jimmyrios do you have an o-scope you can use to check the signals? The wire colors make sense now for your 93, I was looking at a 1996 wiring diagram, but your colors all line up for your year.
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- #88
I doubt someone clipped the coil wire, it probably just broke over the years. What he found is likely the root issue behind the common “dead speedo” issue that many people have experienced. Difference is that he fixed it rather than just replacing the whole cluster like most do.
I’d like to think that his discovery regarding the broken coil wire will help others repair their clusters now in lieu of replacing them outright.
The vss will either produce a square wave or it won’t, there’s really no way for it to soft fail.
ALSO. I just realize that I’ve been referencing it as a sine wave in the last couple of post, the vss produces a SQUARE WAVE not a sine wave.
I’d like to think that his discovery regarding the broken coil wire will help others repair their clusters now in lieu of replacing them outright.
The vss will either produce a square wave or it won’t, there’s really no way for it to soft fail.
ALSO. I just realize that I’ve been referencing it as a sine wave in the last couple of post, the vss produces a SQUARE WAVE not a sine wave.
tmxmotorsports
SILVER Star
Cool info
It may not be able to soft fail, but it's down under the vehicle where the contacts on the connector can corrode and make poor connections, wires partially cut, etc... Looking at the signal with a scope answers all the questions. Is the signal there at all? Does it disappear when you hook up other parts (ECU,TCU,CC, etc..) (shorted output)? . You can kind of guess with an A/C reading on a DMM, but still not be sure what you are seeing. You should be able to put a DC meter on the combination meter's R/G VSS input wire and rotate the drivetrain slowly and see it cycle between about 12V and about 0V as you slowly rotate it. You should be able to see the same signal this way on the B/R output wire from the combination meter.
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- #91
Sure, your method of identifying the waveform is sound I would just say that for most people it's easier to first verify the circuit is intact by testing for continuity with a simple multi-meter (it's also what I would do before getting my scope and laptop out). Because it's way overkill to hook up an O-Scope to the VSS signal wire at the CC ECU just to discover there is no signal, you arrive at the same conclusion you would've with a $10 multi-meter just with a several hundred dollar diagnostic tool that takes 10x longer to set up.
You can get handheld, battery powered ones on Amazon for less than $50. Sure they aren't the best but for basic jobs like troubleshooting cruise controls or any other non DC signal issue, they are quick, easy and cheap. But yes otherwise a multi meter and slow rotation is the way to go.
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- #93
No I’m saying that before you even look for a square wave you just test tone the wire to verify the pathway of the circuit is intact.
All you need for this is your multimeter set to continuity then one probe at the signal output at CC ECU and the other end under the rig on the vss. If it beeps then you e verified it’s good, if not then it’s not worth looking for a signal wave because you need to fix the wiring issue first.
All you need for this is your multimeter set to continuity then one probe at the signal output at CC ECU and the other end under the rig on the vss. If it beeps then you e verified it’s good, if not then it’s not worth looking for a signal wave because you need to fix the wiring issue first.
Fair point. A broken connection would certainly need fixed first
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.
Thank you Sbman...I ll surely do al the testing you say...and post back the results. Sadly i do not have an O-scope just a digital multitester to verify the signal at the moment. I ll look for the B/R wire
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- #96
I would bet $100 that there is nothing wrong with your signal, The fact that your speedometer is now working fine is the indicator of that.
I'd bet it's a connection issue or wiring issue on the signal circuit to the CC ECU.
I'd bet it's a connection issue or wiring issue on the signal circuit to the CC ECU.
We ll see...
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- #99
You can get new hand held o scopes that are also multimeters from amazon for $80. I personally use and recommend picoscopes as they interface with your laptop and make setting, viewing and sharing recordings of incredibly easy.
Pico scope 2204
Pico scope 2204
I looked at getting a picoscope before I bought a used analog scope. My problem with them is lack resolution and variability. It's easy to convince yourself you're seeing something that isn't there, or vice versa, if you don't read and understand the specs.
For most automotive troubleshooting, you're right, the picoscope is sufficient, but that's only true if you're following the "find the bad component and remove it" procedures.
For most automotive troubleshooting, you're right, the picoscope is sufficient, but that's only true if you're following the "find the bad component and remove it" procedures.