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Discussion Starter · #1 ·
I am working on a 1996 Nissan with a Crankshaft sensor problem but my question is not about that specifically, it is instead about sensor function. The Haynes repair manual (I know :rolleyes: ) says the usual, test the circuit by checking the ground wire for proper grounding and for a reference voltage of about 5 volts. This thing has only two wires going to it, a black one and a white and assuming the black is ground that means the white should have the 5 volts on it. If I correctly understand the operation of most sensors I don't understand how one could use a "reference" voltage and only have two wires? :confused: How can a sensor function with only a ground wire and a reference voltage wire? What about the signal? This is a hall effect type sensor and I am wondering how such a sensor could supply any kind of signal if one wire is ground and the other is "hot" with no separate signal wire, is this possible or is this just another case of Haynes (or Chilton's for that matter) manual nonsense.
 

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A hall effect transducer is a coil of wire wrapped around a magnet. Move a piece of steel by it and it generates a small voltage. It is the same thing as a pickup on an electric guitar.
It only needs two wires, and does not need reference voltage to generate a signal.
 

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Discussion Starter · #4 ·
DanielC said:
A hall effect transducer is a coil of wire wrapped around a magnet. Move a piece of steel by it and it generates a small voltage. It is the same thing as a pickup on an electric guitar.
It only needs two wires, and does not need reference voltage to generate a signal.


That's the way I understand it and the check for 5 volts "reference" voltage just made no sense, BTW there is no voltage on the white wire and the black wire is grounded properly. One more instance of those worthless "repair" manuals being more confusion than help.


Matt, I don't have access to a scope but the resistance reading checks out just fine on the sensor. Also unless I am mistaken this same sensor is used on some Jeeps.
 

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Discussion Starter · #6 ·
1996 Nissan 200SX 1.6 DOHC. The engine problem is intermittent, it will run fine for maybe 15 or 20 miles then suddenly start stumbling and lose power. The last time it did this it barely ran at all for about the five miles to home but after sitting overnight it ran ok, for the few minutes it was run anyway. The only code it pulls up is for the crankshaft position sensor and when the code is erased it will immediately reset it when restarted. I always like to make sure a part is bad (this one $67.70) before replacing it and the simple checks I have done so far does not indicate the sensor itself is bad but it may be. I did a quick check of the wiring from the sensor back to where the harness enters the firewall and did not find anything pinched, burned or frayed. The resistance check on the sensor is well within specs but, lacking a scope, I don't know of any other check I could do so I may have to take a chance on a new one.
 

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last time I diagnosed a no start, the CKP sensor was suspected.. used the osciliscope and found the pattern wasn't right. but it was still doing 'somthing'. it was a 1995 Jeep 2.5L.. replaced and it fired right up... if it's anything like the Chrysler ignition, the ignition won't fire till it gets a good signal from the CKP..
 

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Discussion Starter · #9 ·
In case anyone might be interested I solved the problem with this thing but waited to make sure it was actually fixed before saying anything, I did it this way. Even though the sensor was right on the money, resistance wise, when I checked it with a DVOM I decided to warm it up to simulate a warm engine since it seemed to act up worse when the engine was hot. I took a hair dryer and with a reading of 460 to 465 ohms cold, which is dead on, I started heating with the dryer. Nothing happened at first but as it got warmer the resistance started to increase then suddenly jumped to nearly 650 ohms which is waaaay out of range, it was nowhere near as hot as the engine would get. I changed the thing and now all is well.

Now what this post is really about, is that lying Haynes manual! :mad: If I had of followed the instructions in that stinking thing it would have concluded that the computer was bad, which it most certainly was not. That manual clearly says that a reference voltage of approximately 5 volts must be present with the key on, it clearly states this for both the 2 wire sensor and the later 3 wire systems. It even goes as far as identifying both the black and white wires as no. 1 (white) as the reference wire with the 5 volts and no.2 (black) as the ground. What the dickens did they think that "reference" voltage was to be used for if there was no signal wire! :confused: According to those jokers the next step after verifying a good ground on no. 2 (black) wire is to check for the "reference" voltage on the other wire and since this goes back to the computer it would only mean that the voltage was not being supplied by the computer if the circuit was good, ok bad computer-yeah right! :rolleyes: The fact is that voltage was not there because it was not supposed to be! This is not the first time I have run into garbage like this in those worthless books and I don't know why I still check with sometimes, this time however was the last straw! :spank:
 

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An ohm reading on any sensor is not always the tell all especially on an intermittent problem. I have seen a lot of sensors "OHM Out" and still be bad. You proved it was bad before changing it. I preach that all the time. We get more cars that the owner has changed 4 or 5 expensive parts due to misleading codes and then they bring the car to us.
EGR valves are my favorite, they get needlessly changed all the time
 

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Discussion Starter · #11 ·
T, I am sure you are already aware of this but as long as these computer systems have been around now it is still just about impossible to get some people, even some mechanics, to understand that when the computer sets a code for a certain component or system it is simply saying that component or system is not working properly it is NOT saying the component is bad and it needs to be replaced. Of course sometimes the component is bad but quite often it may not be working properly due to another reason, a good example is an Olds a guy brought to me for an Oxygen sensor. He had already bought the new sensor, the second one in about 4 months, but his problem was a spark plug wire that had shorted on the exhaust manifold causing the erroneous code (which he got from the free trouble code scan at Auto Zone). I too see this all the time when someone will get a code for a component and run out and buy a new one only to still have the same problem, the usual response is "I just don't understand the computer says it's bad"!
 

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oldred said:
T, I am sure you are already aware of this but as long as these computer systems have been around now it is still just about impossible to get some people, even some mechanics, to understand that when the computer sets a code for a certain component or system it is simply saying that component or system is not working properly it is NOT saying the component is bad and it needs to be replaced. Of course sometimes the component is bad but quite often it may not be working properly due to another reason, a good example is an Olds a guy brought to me for an Oxygen sensor. He had already bought the new sensor, the second one in about 4 months, but his problem was a spark plug wire that had shorted on the exhaust manifold causing the erroneous code (which he got from the free trouble code scan at Auto Zone). I too see this all the time when someone will get a code for a component and run out and buy a new one only to still have the same problem, the usual response is "I just don't understand the computer says it's bad"!

I like my scope, it usually doesnt lie to me and I still have a can of cool spray that gets usage once in a while.
 

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Oldred, the function of a hall effect sensor is to generate ac volts as the trigger wheel passes by the sensor. I have found many that ohm good cold, and after heating them up go way out of range.

I recently had a 1994 Pontiac Bonneville 3.8L, that the cam, and crank sensor are made into one sensor. The balancer had 2 trigger wheels, and it was setting a code for the cam position sensor. This one did not change it's ohms when heated, and it was sending the ac volts to the ecu. The eprom in the ecu was the problem with this one. Another shop had replaced the ignition module, cam/crank sensor, and ecu, and could not figure out why it would stall/not start after getting to operating temperature. In closed loop operation, the eprom was changing the fuel injector pulse width from 3.84 average in open loop, to 38.4 average, flooding the engine with fuel. It also stopped setting the cam position sensor code.

Isn't working on cars fun??? :D :D :D
 
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