And now a word about...

Interm-Intermit-Intermitt-Intermittents

  You know them, you hate them, and you  can't escape them. They're the job that comes through the door that makes you wish you'd listen to mom and gone to barber college! The job that has the mysterious symptom or light coming on that only happens when driving home the third night of every second month of the Sunday that comes in the middle of the week! You drive the vehicle from here to Canada with no problem found. What you have my friend is a world class intermittent.

  A good plan of attack my be to head the problem off from the beginning, at the write up when the customer drops off the vehicle or even in the night drop box. Referring  to bulletin # 01-00-89-010E, using Customer Concern Verification Worksheets can be a significant tool to help. They have been proven to;

	Reduce "No Trouble Found"
	Increase customer involvement
	The customer has a perception of "they really listen and understand"
	Reduces having to contact customers for more information
	Saves time during peak write up periods and improves night drop box information
	Ensures the right questions are asked at write up

  For more on customer verification contact worksheets click here.

  But, what we can do,  is try to get it to act up while it is in your bay. A discussion I recently had with a  Regional Service Engineer revealed that almost 40% of the vehicles that approach the "Fix it or buy it back" stage are repaired by finding a loose fitting terminal, ground connection or open in a wiring harness. Let's take a look at ways to get these problems to rear their ugly heads.

  One of the best things you can do is get the "opposite sex" of the terminal involved in the circuit and check the terminal tension. There should be a slight drag on the contacts and no deformities and most important no corrosion! It seems a simple step but one that is often overlooked and can lead to hours  of lost labor. The Delphi terminal kits should have most of the terminals you need. To find the proper terminal in SI go to the connector end views. 

	For more on electrical terminals and Micro 64, click here.
	To get some Hands-On experience diagnosing and replacing terminals, enroll in course number 18043.07 Terminals and Connectors. To see when classes are running in the Northeast Region hit the Schedules page.

  Wiring on these late model vehicles is getting rather thin. Not that it is getting difficult to come by, but it is a smaller gage than usual. With the onset of all the different serial data lines (for more information check out the Serial Data article) a 22 gage wire is becoming the standard issue. The problem is that these harnesses are on the delicate side and have a tendency to break inside the insulation close to the connector ends. In fact another big source of problems is intermittent opens in the harnesses themselves. This is where the good old fashioned wiggle test comes into play. Get in there and work it over a bit, don't be shy, but don't tear it out of the socket either! Common sense and good manipulation of the harnesses are a great way to help cut down on your detective work. Here, a Digital Multimeter can be a big help. Try this when diagnosing circuits that have voltage applied, use the voltage setting to monitor a connector (or length of a circuit) which is suspected of having an intermittent connection but is currently operating normally.

	Connect the J 39200 Digital Multimeter to both sides of a suspect connector (still connected) or from one end of a suspect circuit to the other. This will continuously monitor the terminal contacts or length of wire being checked. See "METER CONNECTIONS" for examples of the various methods for connecting the meter to the circuit.
	Set the meter for voltage. Since the MIN MAX mode does not use auto ranging, manually select the voltage range necessary before proceeding.
	Press the "MIN MAX" button. The meter should read "100 ms RECORD" (100 millisecond record) and emit a 1/4 second beep. The meter is now ready to record and will generate an audible tone for any change in voltage. At this point, you may wish to press the "PEAK MIN MAX" button, which will record any voltage variations that occur for at least 1 millisecond.
	Try to simulate the condition that is potentially causing an intermittent connection, either by wiggling connections or wiring,' test driving or performing other operations. If an open or resistance is created, a voltage will be present and the meter will emit a tone for as long as the open or resistance exists. Any change in voltage will cause the meter to emit a tone for no less than 1/4 second. (Listening for a tone while manipulating wiring is very helpful for narrowing in on an intermittent connection.)
	Use the MIN and MAX values when the meter is out of sight or sound range, in noisy areas or for test driving when it may not be possible to monitor the meter.
	To check the MIN and MAX recorded voltages press "MIN MAX" once for MAX and twice for MIN. A variation between MIN and MAX recorded voltages (unless nearly 0 volts) suggests an intermittent open or resistance exists and should be repaired as necessary. IMPORTANT: The "100 ms RECORD" (100 millisecond record) mode is NOT the amount of time allowed to perform a specific procedure. It is the amount of time used to record each snapshot of information used for calculating "AVG" when in the "MIN MAX" mode.

  The previous diagnostic procedure was written to detect intermittents using the meter set to voltage. Whether using the current, voltage or resistance setting to detect intermittents, it is necessary to connect the meter to the circuit.

Following are examples of the various methods of connecting the meter to the circuit to be checked.

	Backprobe both ends of the connector and either hold the leads in place while manipulating the connector or tape the leads to the harness for continuous monitoring while performing other operations or test driving. (Do not backprobe "weather pack" type connectors.)
	Disconnect the harness at both ends of the suspect circuit where it connects either to a component or to other harnesses.
	Use Connector Test Adapter Kit J 35616-D to connect the meter to the circuit.

  If the system being diagnosed has a specified pinout or breakout box, it may be used to simplify connecting the meter to the circuit or for checking multiple circuits quickly. Also it is a VERY good idea to turn the power off to circuits that are going to be checked for resistance. This can prevent false readings and more importantly, damage to the meter!  Tests that work well for detecting  quickest intermittent  can be performed by setting the meter to the "PEAK MIN MAX" setting. An audible tone will be heard whenever the meter detects continuity for at least 1 millisecond. Doing this can pick up the fastest intermittents, with a duration of one thousandth of a second but don't use it all the time as it will give a beep for even the slightest variation.  The J 39200 Instruction Manual is a good source of information and should be read thoroughly upon receipt of the meter as well as kept on hand for reference during new procedures. 

What about DTCs that won't show?

  Depending on the system that you are working with, you may be able to spot a trend in the operation of the vehicle that can help in diagnosis. One of the basic mistakes techs make is to erase the PCM DTCs before performing the "Capture Info" function on the Tech 2. This will hold on the Freeze Frame and Failure Records of the DTC that set. If clearing the DTC is done, without doing this vital step, you are giving away a lot of useful information! If you do find yourself chasing a DTC and not getting anywhere, don't forget to check out the Diagnostic Aids that accompany the trouble charts. Recently, I had a technician that was experiencing reoccurring DTCs for both O2 sensors being lean on a 99 Intrigue. He tried replacing both sensors, replacing the PCM and checked his fuel pressure as well as taking several snapshots. Under the Diagnostic Aids section it advised him to unplug the MAF sensor and see if the problem cleared up and it did. Replacing the MAF sensor fixed his car and the answer was right there in the DTC chart.

 Other systems will also have their form of Freeze Frame/Failure Records, such as the enhanced DTC function on many of the Chassis Systems like ABS. The Enhanced DTC data will let you look and see how often a DTC is set and other information, however it will not be as thorough as in the PCM.

  Snapshots are a good way to try and nail down an intermittent problem and there are several ways of attacking them. You can try and do some live plotting and graphing using the Tech 2 or you can snapshot the data stream and look at it later on in playback mode on the Tech 2 or use TIS2000 to plot and graph your data. For more on Snapshots click here!

Inducing Intermittent Fault Conditions

In order to duplicate the customer's concern, it may be necessary to manipulate the wiring harness if the malfunction appears to be vibration related. Manipulation of a circuit can consist of a wide variety of actions, including:

	Wiggling the harness
	Disconnecting a connector and reconnecting
	Stressing the mechanical connection of a connector
	Pulling on the harness or wire in order to identify a separation/break inside the insulation
	Relocating a harness or wires

All these actions should be performed with some goal in mind. For instance, with a scan tool connected, wiggling the wires may uncover a faulty input to the control module. The snapshot option would be appropriate here. Refer to Scan Tool Snapshot Procedure . You may need to load the vehicle in order to duplicate the concern. This may require the use of weights, floor jacks, jack stands, frame machines, etc. In these cases you are attempting to duplicate the concern by manipulating the suspension or frame. This method is useful in finding harnesses that are too short and their connectors pull apart enough to cause a poor connection. A DMM set to Peak Min/Max mode and connected to the suspect circuit while testing can yield desirable results.

Certainly, using the senses of sight, smell, and hearing while manipulating the circuit can provide good results as well.

There may be instances where circuit manipulation alone will not meet the required criteria for the fault condition to appear. In such cases it may be necessary to expose the suspect circuit to other conditions while manipulating the harness. Such conditions would include high moisture conditions, along with exceptionally high or low temperatures. The following discusses how to expose the circuit to these kinds of conditions.

Salt Water Spray
Some compounds possess the ability to conduct electricity when dissolved in water such as ordinary salt. By mixing table salt with water in sufficient quantities, you can enhance the conductive properties of water so that any circuit which may be sensitive to moisture will more readily fail when liberally sprayed with this mixture.

Mixing 0.35L (12 oz) of water with approximately 1 tablespoon of salt will yield a salt solution of 5 percent. Fill a normal spray bottle with this mixture. This mixture is sufficient to enhance the water's own conductivity. This may cause the circuit to fail more easily when sprayed. Once the mixture is completed, spray the suspect area liberally with the solution. Then, while monitoring either a scan tool or DMM, manipulate the harness as discussed previously.

High Temperature Conditions

  If the complaint tends to be heat related, you can simulate the condition using the J 25070 Heat Gun.

 Using the heat gun, you can heat up the suspected area or component. Manipulate the harnesses under high temperature conditions while monitoring the scan tool or DMM to locate the fault condition.

 The high temperature condition may be achieved simply by test driving the vehicle at normal operating temperature. If a heat gun is unavailable, consider this option to enhance your diagnosis. This option does not allow for the same control, however.

Low Temperature Conditions

  Depending on the nature of the fault condition, placing a fan in front of the vehicle while the vehicle is in the shade can have the desired effect.

  If this is unsuccessful, use local cooling treatments such as ice or a venturi type nozzle (one that provides hot or cold air). This type of tool is capable of producing air stream temperatures down to -18°C (0°F) from one end and 71°C (160°F) from the other. This is ideally suited for localized cooling needs.

  Once the vehicle, component, or harness has been sufficiently cooled, manipulate the harness or components in an effort to duplicate the concern.

Using TIS 2000   

  Another weapon in your arsenal is to take the Snapshot you got from the Tech 2 and upload it to the Techline PC and plot and graph it using the program. Doing this gives you a larger screen and multiple color format to look at to give you a better view of the glitch. For more on Snapshots and plotting and graphing click here!

For more on intermittent issues, check out; Technology Close Up for June 2007  Course #10207.14D  Intermittent Diagnosis and download the Job Aid that goes with it. They can both be accessed at gmtraining.com.