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Photos: Bob Pattengale, SPX/OTC & Snap-on; illustration: David Kimble; graphic design: Harold A. Perry

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re you using the full power of your scan tool? My experience has shown that many technicians use a scan tool only to retrieve diagnostic trouble codes (DTCs) and look at parameter data, while overlooking other powerful features. One of these overlooked features is bidirectional control, and most enhanced scan tools have this capability. Bidirectional control is a generic term used to describe sending and receiving information between one device and another. The vehicle engineers responsible for designing computer control systems programmed them so a scan tool could request information or command a module to perform specific tests and functions. Some manufacturers refer to bidirectional controls as functional tests, actuator tests, inspection tests, system tests or the like. Reinitialization and reprogramming also can be included in the list of bidirectional controls. This article will explain the benefits and limitations of bidirectional controls and demonstrate how they can be used in the diagnostic process. Specific scan tools are mentioned for illustrative purposes only. No attempt was made to evaluate every available tool. The scan tool is the primary bidirectional control device and could actually be called a bidirectional tool, because it sends information to, and receives information from, vehicle control modules. For example, in the case of OBD II generic information Mode 1 (which relates to data parameters), the scan tool user initiates a request for information from the powertrain control module (PCM), and the PCM responds by sending the information back to the scan tool for display. Most enhanced scan tools also have the ability to actuate relays, injectors and coils, perform system tests, etc. Fig. 1 on page 40 shows several screen captures taken from a 2004 Honda Civic, using the Teradyne Pocket Tester. The bidirectional controls for this vehicle are listed under the Inspection Menu and, as you can see, many useful tests are available. The technician can turn the fuel pump on and off,

BIDIRECTIONAL SCANNER CONTROLS: THE 2-WAY DIAGNOSTIC HIGHWAY BY BOB PATTENGALE

Maintaining an up-to-date array of diagnostic equipment will cost a pretty penny. But it’s a downright waste of money if you aren’t exploiting the full capabilities of the equipment you already have. cycle the a/c clutch on and off and perform an evaporative emissions leak test. The options programmed into both the vehicle and the scan tool will determine the range of options available. This brings up a key question: Are there differences among scan tools? Everyone knows the answer is yes. Designing and building scan tools is a difficult process for vehicle manufacturers and aftermarket scan tool manufacturers. Automakers spend lots of time and money designing the best possible diagnostic tool for their product lines. Cost is a consideration, of course, but they don’t have the luxury of deciding what to leave out. The diagnostic platform must communicate with and diagnose all possible systems. Aftermarket scan

tool manufacturers, on the other hand, have a slight advantage in knowing what the factory scan tool is capable of doing. But these companies have several issues to consider that don’t concern their OEM counterparts. Here are a couple that relate to bidirectional controls: •Is the information available from the vehicle manufacturer to build an aftermarket scan tool? If the vehicle manufacturer makes the design information for scan tool bidirectional control available, in most cases building an aftermarket version is simplified. But this does not mean it will be easy or cost-effective. Bidirectional controls are the most difficult feature to implement. Two issues are liability and safety. For example, it would not be wise for a

technician to command an increase in engine speed if the transmission were in gear and the brake not applied. To avoid damage to the vehicle and/or personal injury, some type of protection must be implemented. In some cases, this protection was programmed into the vehicle module; in others, the protection was designed into the scan tool. An aftermarket scan tool manufacturer needs to know this information. •What are shop owners and technicians willing to pay for an aftermarket scan tool? Each scan tool maker must evaluate the cost involved in building a scan tool and determine the options most important to technicians. In the past, most of the computer technology was designed into engine control sys-

tems, so the primary focus was on building a good engine diagnostic tool. Even with this focus, many aftermarket scan tools do not include all the parameters and tests available in the factory scan tool. Many shop owners and technicians have made the decision to purchase the factory scan tools to ensure all the information is available. This is becoming more of an issue when dealing with nonengine control systems—e.g., antilock brakes (ABS), supplemental restraint systems (SRS), climate control systems, electronically controlled transmissions, body control systems and the like. Aftermarket scan tool companies need to increase the level of coverage built into their equipment to stay competitive. Aftermarket scan tool makers have

done a good job of working through the issues. But don’t be surprised or upset if you pick up a factory scan tool and find it has features or tests not available on your aftermarket tool. Each is built for a different market and therefore must satisfy different objectives and needs.

Getting Down to Diagnostics When properly utilized, bidirectional component and system tests can significantly reduce your diagnostic time. Consider a no-start situation. You’ve connected a fuel pressure gauge, cycled the key and cranked the engine, but no fuel pressure was measured. At this point you don’t know if the problem is a component, a circuit or com-

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BIDIRECTIONAL SCANNER CONTROLS: THE 2-WAY DIAGNOSTIC HIGHWAY mand-related. The scan tool you’re using has a fuel pump command available. Using the scan tool, command the fuel pump on. If the fuel pressure gauge now shows proper fuel pressure, you know the fuel pump circuit and pump are functioning properly. Your diagnostic focus should move to the command side of the circuit. The PCM may not be receiving the necessary enabling criteria to active the fuel pump circuit. This may be caused by a faulty input sensor, low oil pressure or some other factor. The process described above took less than five minutes. If you had to manually test the fuel pump circuit, it would likely take three times as long. As another example, a Honda Civic recently rolled into my shop with the malfunction indicator light (MIL) illuminated. I retrieved the DTCs and found a

P1404 (EGR Stuck Closed). At this point I had to determine if the problem currently existed or if it was an intermittent. Fig. 2 shows screen captures from the Teradyne Pocket Tester. Box 1 shows the EGR Test under the Inspection Menu. To the right of the EGR Test is a box circled in red. This is an information box; when selected, it will provide details about the test you’re about to perform. Box 2 provides critical instructions related to the test. Box 3 shows the start of the test process. Box 4 instructs you to increase the engine speed to between 2500 and 3000 rpm. Box 5 shows a sample of the data being considered during the test. The bar graph in the center is for the EGR Lift Sensor. Based on the reading, it looks like the EGR Valve is functioning at this time. Box 6 shows the results of the EGR Test. The system is normal at

Fig. 1

Screen captures: Bob Pattengale

Fig. 2

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this time. If you suspect the EGR valve may be sticking intermittently, you might want to run this test several times. If the EGR valve test failed a subsequent test, you could proceed with checking and/or replacing the EGR valve. I also recently serviced a 1995 Dodge Stratus with an illuminated MIL. The DTC was a P0443 (Evap Purge Solenoid Circuit). The diagnostic information shows the DRB III factory scan tool is capable of commanding the purge solenoid open and closed. The Vetronix Mastertech and Snap-on Scanner also can perform this test. Fig. 3 on page 42 shows screen captures from the Vetronix Mastertech 3100. Box 1 shows the F6: Purge Test option. Box 2 provides the option of blocking or permitting purge flow. In this case, we need to select F1: Flow. Box 3 provides a suggestion: An inspection of vacuum lines and hoses may reveal a problem. This is an important note; many problems can be discovered quickly with a visual inspection. Box 4 explains that the up and down arrows on the scan tool control the purge solenoid. Box 5 displays the initial Long Term Adaptive Fuel Trim values for Banks 1 and 2. Once the purge valve is commanded open, we expect the fuel trim values to change based on what’s present in the gas tank. If there’s a high concentration of fuel vapors present, the fuel trim will decrease to compensate for the rich air/fuel mixture condition. If there’s a high concentration of oxygen, the fuel trim will increase to compensate for the lean air/fuel mixture condition. In Box 6, the purge valve was commanded on. The upper box shows the initial test: no change in fuel trim. At this point, I suspected a sticking purge solenoid. I cycled the purge valve on and off several times and on the third try, the fuel trim levels increased, indicating the solenoid opened. Based on the results, the purge solenoid should be replaced. The next vehicle is a 2004 Toyota Camry with the SRS and Passenger Air Bag lights illuminated. This vehicle was sent to us by a body shop, following accident repairs. A Mastertech

BIDIRECTIONAL SCANNER CONTROLS: THE 2-WAY DIAGNOSTIC HIGHWAY with Toyota software is needed to access this system. For most shops, diagnosing and repairing this problem would not be an option, unless they have the necessary equipment. Using the Mastertech, I retrieved DTC B1782 (Occupant Classification Sensor Rear LH Circuit Malfunction). After consulting the diagnostic information, a visual inspection revealed the Rear LH sensor connector was not fully connected. Fig. 3 Figs. 4-6 are screen captures taken from the Mastertech. In Fig. 4, Box 2 shows the controller options for this vehicle. After properly connecting the sensor, we should check the sensor data (Box 3). In Box 4, all of the sensors are reading, but the sensor weights range from 5.50 to 6.60 lbs. The diagnostic chart recommended performing a Zero Calibration after seat replacement. Fig. 5 shows the screen captures related to Zero Calibration. Box 1 Zero Calibration is option 5. Box 2 and Box 3 provide specific instructions to prepare for the test. Box 4 indicates that Zero Calibration is complete and recomFig. 4

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the 59 to 73 lbs. recommended. As you can see, this repair would not have been possible without the proper equipment. In addition to an enhanced scan tool with bidirectional controls and OEM software, a weight set is needed to properly perform this test.

When Bidirectional Control Won’t Work

mends performing a Sensitivity Check. Fig. 6 shows the screen captures related to the Sensitivity Check. Box 1 Sensitivity Check is option 6. Box 2 provides instructions to begin the test. Box 3 is the first sensor reading measurement. The sensor reading is 0.00 lbs., which passes the 7 to 7 lbs. test. Box 4 indicates that 66 lbs. of weight need to be placed on the seat. Box 5 shows three weights—50 lbs., 10 lbs. and 5 lbs.—for a total of 65 lbs., placed on the seat. Box 6 shows the sensor reading with the weights applied. The reading is 66.00 lbs., which agrees with the weight we applied and falls within Fig. 5

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These examples show just a few of the ways that bidirectional controls can be used. The scan tools used provided information on how to prepare for the tests and explained the test actuation procedures. However, you may run into a situation where a bidirectional control will not actuate or stops working without your control. Fig. 7 on page 46 is a combination screen capture from EASE Diagnostics and Vetronix scan tools that illustrates this possibility. The EASE Chrysler Enhanced software displays information related to bidirectional controls. The Test Description box in the upper left-hand corner indicates the purge solenoid will cycle on and off approximately every 1.5 seconds. The Notes box in the upper

right-hand corner indicates the solenoid will timeout after seven minutes. The white box with blue border in the lower right corner shows Mastertech screen captures from a 1995 Dodge Stratus. In red are two boxes labeled Time On and Time Off. At 3:52:59 p.m., I commanded the purge solenoid on. Approximately 30 seconds later, at 3:53:32 p.m., the solenoid turned off. This automatic-off procedure is designed to protect the solenoid. Depending on the component or test, the solenoid may turn on again after a specific period of time. This example demonstrates that the information provided to the scan tool manufacturers is not always accurate. Is this a significant issue that will prevent me from diagnosing this vehicle? No. I had a basic understanding of what the test was going to do and the test performed the necessary function: opening and closing the purge solenoid. It would be nice if the information were accurate, but in many instances, the information is released to the scan tool designers before the first production vehicles have even left the assembly plant. Vehicle engineers can and do make changes after this point that are not reflected in the original scan tool design specification. Also, once vehicles are on

the road, PCM reprogramming can change bidirectional control specifications and operation in ways that are not reflected in the scan tool information. There’s a lot more that could be written about bidirectional controls and their place in your diagnostic routine. But how much more? Until recently, I wasn’t even sure how many bidirectional functions and tests were available for each of the current scan tools. To get a general idea, I called Bob Augustine at Vetronix and asked about the capabilities of the Tech 2. As it turns out, GM has a set of documents called the Tech 2 Pathing Tables. These are basically three separate documents: Body, Powertrain and Chassis. All together, they’re 14 pages long and list more than 1300 tests in alphabetical order—1300 tests! If you own a Tech 2, you need these documents, which can be purchased from ACDelco at acdelcotds.com/store. All three sections are sold as a set for $25 under Part No. ROM00190. Simply insert the part number into the Item Search box and select Search. The document is displayed with a description and cost. GM also offers a handy pocket reference card, Part No. ROM00164. Here’s an example of how the Pathing Tables can help: A GM vehicle equipped with electric mirrors is

Fig. 6

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BIDIRECTIONAL SCANNER CONTROLS: THE 2-WAY DIAGNOSTIC HIGHWAY not working properly. You’d like to test the operation of the Driver’s Electric Mirror using the Tech 2, but don’t know where to find the specific Fig. 7

tests. Using the Body Pathing Table, simply look up Driver’s Electric Mirror in the alphabetical chart. Driver’s electric mirror functions are located in:

Body-Memory Mirror Module-Special Functions-Output Controls. From here you can command the mirror Down/Left/Right/Up. Among the other function tests I found interesting are Incandescent Dimming, Microphone Test, Military or Standard Time, Phone Call Test/OnStar and Theater Dimming. This is just one vehicle manufacturer and one factory scan tool. Multiply this by 22 vehicle manufacturers and you can see that the scan tool’s potential power is incredible. Can you afford to work only on older vehicles and limit yourself to just engine control systems? Maybe, but for how much longer? My advice is to get ready to invest a lot more money in scan tools. The benefits will far outweigh the cost in the long run. Visit www.motor.com to download a free copy of this article.

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