PicoScope 7 Automotive
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EGR stepper feedback / waveform
EGR stepper feedback / waveform
Toyota Yaris 07
Had 3 new EGR valves, latest one is a Denso, none lasted more than a few months.
These use a stepper motor.
I can bidirectionally control it and see that the feed back does not match the required position once it gets above 11 steps actual position starts to jump around, fault sets and the I can hear the stepper motor making nasty noises.
This is voltage and current through the green wire and from what I can find on line the 33v spike seems to normal.
However I am at a loss from the wiring diagram how the ECU is getting the feedback position and other than the step pulses what I should be seeing. Had to cut this one short and will be looking at all 4 wires but need to understand what I am seeing. Black is B+
Could the white and yellow be looking for that spike to confirm the motion has happened and be using that to count position?
There might be a known good EGR stepper on the Pico library but it's not searchable that way. That reverse current down spike concerns me, wondering if there should be a diode/clamp in the ECU that should stop that.
Input on theory/operation welcome!
Had 3 new EGR valves, latest one is a Denso, none lasted more than a few months.
These use a stepper motor.
I can bidirectionally control it and see that the feed back does not match the required position once it gets above 11 steps actual position starts to jump around, fault sets and the I can hear the stepper motor making nasty noises.
This is voltage and current through the green wire and from what I can find on line the 33v spike seems to normal.
There might be a known good EGR stepper on the Pico library but it's not searchable that way. That reverse current down spike concerns me, wondering if there should be a diode/clamp in the ECU that should stop that.
Input on theory/operation welcome!
Re: EGR stepper feedback / waveform
Got back on this today
Pic and waveform attached. According to scan tool control I asked for steps to 50 (out of 125) it then seems to revert to 0 or 2 in this case however there was no change in engine note at all. The car however on sporadically sets a code. really need a known good to call it another bad part or EGR not grounding it fully
Channek colours are matched to dwg above Blue = White
Pic and waveform attached. According to scan tool control I asked for steps to 50 (out of 125) it then seems to revert to 0 or 2 in this case however there was no change in engine note at all. The car however on sporadically sets a code. really need a known good to call it another bad part or EGR not grounding it fully
Channek colours are matched to dwg above Blue = White
Re: EGR stepper feedback / waveform
Hi.
.
There is an error on the diagram.
The correct scheme looks different.
Here is the manual (DTC P0400) :
https://mega.nz/file/U1phAKJJ#dWiq1XDWy ... fv0W4_guQw
.
.
There is an error on the diagram.
The correct scheme looks different.
Here is the manual (DTC P0400) :
https://mega.nz/file/U1phAKJJ#dWiq1XDWy ... fv0W4_guQw
.
- Attachments
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Re: EGR stepper feedback / waveform
That's brilliant, thanks for your time to extract that and post it.
Makes more sense now. I would suspect the MAF sensor but when they replace the EGR valves it gets better and the code goes for months.
The waveform they show appears to have the wrong scale on it but mine still has that drop out on all 4 poles, whilst they might be assuming a lower sample rate I would expect that to be shown.
Makes more sense now. I would suspect the MAF sensor but when they replace the EGR valves it gets better and the code goes for months.
The waveform they show appears to have the wrong scale on it but mine still has that drop out on all 4 poles, whilst they might be assuming a lower sample rate I would expect that to be shown.
Re: EGR stepper feedback / waveform
I saved the red trace as a reference then aligned it with the blue.
Looking at the odd section and comparing them I think the ECU may be struggling to pull it to ground. The vertical drop is vertical as if it is being switched.
Also looking a the current it seems to reverse at that point.
One other thing looking carefully at the bottom of that section it is -ve voltage
Can that only happen if there is a bad ground inside the ECU ?
Found an example where it is obviously not pulling it to ground, this was a command for just 2 steps.
Looking at the odd section and comparing them I think the ECU may be struggling to pull it to ground. The vertical drop is vertical as if it is being switched.
One other thing looking carefully at the bottom of that section it is -ve voltage
Found an example where it is obviously not pulling it to ground, this was a command for just 2 steps.
- Attachments
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- 20221114-0001 0 to100 no engine n6te change.psdata
- (8.12 MiB) Downloaded 140 times
Re: EGR stepper feedback / waveform
The image of the signal from the manual is very conditional.
It does not show voltage spikes characteristic of switching drivers of the inductive winding of the motor.
You can assemble a simple emulator of four low-power lamps with close resistance.
By connecting this homemade emulator to the EGR connector, you will receive pure rectangular pulses that will follow in the opposite phase for each motor winding.
Now - all issues related to the electrical part will disappear.
It will remain to deal with the flow of exhaust gases through the section of the EGR valve.
When the EGR valve control is activated from the scanner, you can change the direction and number of steps of the motor.
At the same time, you should get a change in the parameters of the amount of air entering the engine.
It is more convenient to control this by the signal of the oscilloscope connected to the MAF.
In order for the effect of the control change to be more obvious, you can activate it by maintaining RPM=2000-3000.
It does not show voltage spikes characteristic of switching drivers of the inductive winding of the motor.
You can assemble a simple emulator of four low-power lamps with close resistance.
By connecting this homemade emulator to the EGR connector, you will receive pure rectangular pulses that will follow in the opposite phase for each motor winding.
Now - all issues related to the electrical part will disappear.
It will remain to deal with the flow of exhaust gases through the section of the EGR valve.
When the EGR valve control is activated from the scanner, you can change the direction and number of steps of the motor.
At the same time, you should get a change in the parameters of the amount of air entering the engine.
It is more convenient to control this by the signal of the oscilloscope connected to the MAF.
In order for the effect of the control change to be more obvious, you can activate it by maintaining RPM=2000-3000.
Re: EGR stepper feedback / waveform
Thanks again Vasek. An emulator is a great idea (10W bulbs should be pretty close) - as is scoping the MAF, as my ears were telling me that despite asking for 100 steps on the scan tool I had no change in engine note. I'll get back on it next week.
If I need to, can I re-code a used ECU with Techstream ? I don't see many Toyotas.
How does the ECU know the position of the EGR, I see no feedback circuit. Is it just counting ?
If I need to, can I re-code a used ECU with Techstream ? I don't see many Toyotas.
How does the ECU know the position of the EGR, I see no feedback circuit. Is it just counting ?
Re: EGR stepper feedback / waveform
Forgot to update this used 4 10w bulbs to take the EGR out of it.
So when I bi-directionally control say 100 steps (first activity) it, it's a mess with the ECU not pulling the load to ground.
But when it then reverts back after a few seconds, its perfect. As these are just resistive loads what is the difference !?
Full file https://www.dropbox.com/s/5rgq5vrpautvv ... sdata?dl=0
So when I bi-directionally control say 100 steps (first activity) it, it's a mess with the ECU not pulling the load to ground.