The Trans harness pic shows the Input Shaft Speed Sensor as a variable reluctance type with a coil resistance of around 1kΩ. So that's what you've got if that pic indeed relates to your car model.
Excellent. Thank you for your patience and explanation. I had some general ideas, but nothing specific. So in a nutshell, if I understand correctly, the 13 volt DC signal will be the Vin and the comparator can be adjusted for the desired output with potentiometer? If I can simply adjust for 7,8, 10 VAC output, I have achieved what I need. Thanks.
Since it only has two wires, could it be that both wires are AC self generating output, with no need for a voltage supply signal from the car's battery? For comparison, I read that 3 wire Hall sensor needs a reference voltage signal.
Yes.
A typical Hall sensor has a +ve supply wire, a ground wire and a signal output wire.
Both of those understadings are wrong.
If it is a hall effect sensor, one wire must be to the 12V power, and the other is the signal out.
If it is a coil, it is truly putting out AC , and , to duplicate the original signal exactly, you would need an isolated, bipolar supply. But, based on the results others have seen, this should not be necessary.
To know exactly what would and would not work, we need to know what each wire is connected to in the ECU. For example, one of the two connections at the ECU is ground or 12V, we would need to design the circuit with that constraint.
Bob
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Thanks Bob ! Could it be possible to be a two wire Hall sensor; one with supply voltage and one with output?
Update: I hooked the multi-meter to the two wires inside the car and drove it. Look at my picture below and see the results. The one that is most puzzling to me is the meter positive lead hooked to red/white wire and the negative lead hooked to ground. At idle, and parked I get DC battery voltage (12-13 volts DC). However, while driving I can switch the meter to AC and now the signal varies 1.0 to about 4.0 VAC. Switching bac to DC again yields 12-13 VDC. How can I simultaneously get AC and DC? Any way I can boost this 4.0 VAC to 7, 8 or 10 VAC with a small amp or comparator circuit and solve this problem ? Thanks, sorry for dragging this out.
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You can have a voltage that is the sum of a DC component and an AC component (see e.g. here).
With an ordinary multimeter:
When the meter is in DC setting, it will average the AC component if the frequency is more than a very few Hz. The average of an AC component is 0 V, so the meter displays the DC component only.
When the meter is in AC setting, typically a capacitor blocks any DC component. The remaining AC component is rectified, measured and displayed.
Og course, there exist advanced meters that perform so called RMS metering. These meters will calculate the RMS of the combined voltage and will in the case of a mixed waveform thus display a different value than an ordinary multimeter.
You can use a series capacitor to block the DC component, then use an ordinary amplifier to boost the remaining AC to the desired level.
As has been pointed out, the signal driving the ECU/PCM needs to track the frequency of the signal from the sensor. That means the sensor signal needs to be reliable; but if the sensor triggers the error code then presumably the sensor or the connectors/harness has a fault?
Thanks again, very helpful. If it's no trouble, can you maybe post a schematic or drawing of the circuit, including how to input the DC battery voltage and the output "amplified" AC? Remember, I only need 8-10 VAC to send to the computer to "fool" it into thinking the sensor is good, thus turning off the check engine light, and passing the visual test at the smog station. Thanks, we are getting there !!t
Bearing in mind the previous discussions, can one of you draw up a quick schematic of how exactly I need to build it on a circuit board, how to feed the voltage in and out. I know this is asking a lot, but I really want to get it right, so I don't blow the fuse, PCM or other circuit. Really, thanks for everything. This has been a big help.
Do they only do a visual test in the US? In Europe the test involves exhaust gas analysis at different rpms, so the error light would promptly come on again and the test would fail. A certain European car manufacturer fell foul of trying to cheat the emissions test.
Yes, and tougher requirements here in California. The first thing the smog inspector does is to verify the "Check Engine" light is off. If it is on, the test is over, automatic failure. Then they check for tampering or missing equipment. If the visible test passes, then they move onto the emissions tailpipe test and idle and 2500 RPM. The visual is my problem. I need the op amp, comparator circuit, transformer or whatever, to feed back into the speed sensor line to "fool" the computer into thinking there is no fault, and thus turning off the "Check Engine" light. I really only need help now with the schematic of how to build the circuit with what has been recommended in this thread. Once the circuit is in place, I can clear the code, go to the smog station, and be done with this. Thanks for any help !!
These questions have not been answered. Until they are this thread is going to be tantamount to a fishing expedition.
Chris
Sorry to bang on, but I'm still having a problem understanding the logic behind this. Correct me if/where I'm wrong :
1) If the ISS sensor output is only 1.5VAC at idle, it (or its connection) is faulty.
2) If you build a circuit which has output pulses whose negative-going excursions go at least abou 7V below the battery +ve voltage you can clear the error light.
3) The visual test will pass.
3) The inspector will then proceed to do the emissions test.
4) The test is done at more than one input shaft speed.
5) Your faulty ISS will be in use for the emissions test.
6a) The built circuit is also in use during that test. If the test is passed you have cheated the test.
OR
6b) The built circuit is not used for the emissions test. The error light will come back on. The test is failed.
6c) Cheating the test is illegal where you are.
Note: Encouraging unlawful activity is forbidden by the Terms of Service of this site.
1) If the ISS sensor output is only 1.5VAC at idle, it (or its connection) is faulty.
2) If you build a circuit which has output pulses whose negative-going excursions go at least abou 7V below the battery +ve voltage you can clear the error light.
3) The visual test will pass.
3) The inspector will then proceed to do the emissions test.
4) The test is done at more than one input shaft speed.
5) Your faulty ISS will be in use for the emissions test.
6a) The built circuit is also in use during that test. If the test is passed you have cheated the test.
OR
6b) The built circuit is not used for the emissions test. The error light will come back on. The test is failed.
6c) Cheating the test is illegal where you are.
Note: Encouraging unlawful activity is forbidden by the Terms of Service of this site.
It is not illegal if the code is cleared, as the onboard diagnostics allow the owner to do this, and I already have cleared it several times. The car otherwise passed the tailpipe emissions test, which the system has not been tampered with. Emissions system tampering is illegal, no electronic controls under California and Federal laws. The transmission is not part of the emissions test, but they lump any light into the test. The local smog referee has the authority to waive any requirement, but cannot see me for a few months.
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