How do I check for resistance on the crank sensor and CAM sensor what the number should be

Tiny
RUSS1953
  • MEMBER
  • 2004 GMC ENVOY
  • 4.2L
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 28,000 MILES
Engine will turn over but will not start. What all do I need to check that caused the no spark? There is voltage at the power side on coils and good ground, but I did not check for a signal. How do I check for signal at the coils, crank sensor, and cam sensor? How do I check for voltage at the crank sensor? How do check injectors for a signal and where are they located?
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Sunday, December 25th, 2016 AT 10:14 AM

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Tiny
CARADIODOC
  • EXPERT
This stuff is all checked for you by the engine computer. You cannot check the cam or crank sensor with ohm meter readings. A voltage is generated in them as in older versions, but then there are a bunch of internal circuitry that processes that signal. You cannot read through that circuitry with an ohm meter.

You need a scanner to view live data. That will include the cam and crank sensors and an indication as to whether their signals are showing up at the computer. You may also have a diagnostic fault code for a missing signal, but that does not necessarily mean the sensor is at fault. Fault codes only indicate the circuit that needs further diagnosis. A sensor becomes suspect after wiring and connector problems have been ruled out.
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Sunday, December 25th, 2016 AT 11:56 AM
Tiny
RUSS1953
  • MEMBER
I have a Innova 3040c scanner it can view live data, but the technical support said the engine have to be running before this scanner will view live data. What kind of scanner I need to view live data?
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Sunday, December 25th, 2016 AT 10:19 PM
Tiny
HMAC300
  • EXPERT
They all work that way.
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Monday, December 26th, 2016 AT 7:08 AM
Tiny
CARADIODOC
  • EXPERT
The Innova 3040c is not much more than a fault code reader except it can also access Anti-Lock Brake Computers in addition to Engine Computers. The units I have used that display live data only updated about once every three or four seconds which makes them useless for watching for momentary glitches. This model is a little more advanced than the basic fault code readers, but it is worlds away from doing what regular scanners do.

To begin with, no scanner requires the engine to be running to display data. If that were the case, they would be totally useless in diagnosing crank / no-start problems. Also, many sensor circuits can be diagnosed quite easily without having to have the engine running. All that is required is to have the ignition switch turned on so the computers are turned on and working.

Next, by the mid 1990's almost all cars had at least six to eight computers, and by the late 1990's some models had up to forty seven computers. Professional scanners can access all of them. Your tester only accesses two, the Engine Computer and the Anti-Lock Brake Computer. The fact it can access ABS Computers on a few car brands sets it higher up on the evolutionary scale than all other simple code readers.

One of the biggest advantages of scanners is they are "bidirectional", meaning you can talk back to the computers as well as listen to them. A code reader might display a fault code for a problem with the electric radiator fan circuit, for example, but a scanner will let you command the engine computer to pulse the fan relay on and off so you can take test measurements in that circuit. A few quick button presses will show if the circuit is working. In the course of a day, that can save a mechanic many hours of diagnostic time that translates into lower repair costs for his customers.

I have a Chrysler DRB3 scanner because with a few extra plug-in cards, it will work on any Chrysler vehicle back to 1983 models, which includes most of what I own. With another card, it will work on any brand of car starting with 1996 models, but only for emissions-related stuff. For that reason, a lot of independent shops bought them. 2004 was the first year that scanner became obsolete on the Dodge Dakota, and it no longer worked on any model after 2007. I do not know if it will work on your truck, but regardless, it is not the best choice for you because it is limited to the engine computer.

A better choice would be something sold by the guys who drive the tool trucks and visit repair shops each week. The mechanics at any dealership or independent shop can tell you when each salesman visits them. Be aware though, they are usually there for one hour, and must adhere to a pretty strict schedule. Some shop owners only allow their mechanics to run out to those trucks during their lunch breaks or other scheduled break times. The salesmen are usually busy too replacing or repairing broken tools, placing orders, and things like that. You might have to wait until just before the truck is ready to leave for the next stop.

Many mechanics buy their own scanners so they do not have to wait for the one they share in the shop. They often trade them in to upgrade to something newer and better. Once you are on the tool truck, ask if they have anything in the "used" drawer, or if they know of a trade-in that will be coming in soon. You can also ask at some local shops if they have a scanner they would like to sell. Sometimes they kept an old one in case an older car came in, but now they are ready to part with it so they can use the dollars to buy the newer model. You will find a lot of used scanners on eBay too, but you have to worry about whether everything works right and all the needed cables are included.

The most popular brand of aftermarket scanners is Snapon", but their products are very expensive. They also charge way too much for annual updates, which you may not need. Do a search for their "Modis", Ethos", and "Solus". My friend had a Modis, but Snapon wanted it back for some reason. They upgraded him to a Solus at a good price. New, it sells for around $3,500.00, which is not too bad, but they want $1,500.00 per year to update it.

Another popular scanner is the "Genysis". My school had two of those, but I did not use them very often. The common tool truck companies are MAC, Matco, Cornwell, and Snapon. All of them have their own scanners, but most are just rebranded units made by other companies.

You might also do a search for Snapon's "MT2500". We called that "the red brick", because, well, it looks like a red brick. You need to buy two plug-in cartridges, and you may need different cartridges for different computers, but if I understand correctly, that will work on vehicles up to 2010. You would have to check to be sure it will do what you need it to do.

All of these scanners update their screens multiple times per second, as opposed to once every three to four seconds for the hundred-dollar models. Most will also have a "record" feature that allows you to record a snapshot of a few seconds of sensor data that can be played back slowly, later. You press the "record" button when the problem occurs during a test-drive. Because the data passes through the scanner's memory, the recording actually begins a couple of seconds before you pressed the button. When you playback the recording, you can watch if the signal drops out for a sensor that affects how the computer is running the engine, meaning an input sensor, and you can watch the results of how it is running the engine with other sensor readings, mainly the oxygen sensors and engine operating conditions. The common things are idle speed and fuel trim numbers. Being able to view that data provides many times more information than simply reading a diagnostic fault code.
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Monday, December 26th, 2016 AT 11:12 AM
Tiny
RUSS1953
  • MEMBER
Thank's for the information.
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Monday, December 26th, 2016 AT 1:32 PM

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