Important:  Understanding the DTC table and using it correctly will reduce diagnostic time, and prevent the unnecessary replacement of parts.

After the visual/physical inspection is complete, the Powertrain On Board Diagnostic (OBD) System Check should be performed. The OBD System Check will provide direction to diagnose the following conditions:

The Powertrain OBD System Check is designed as a master table for driveability and emissions system diagnosis. The OBD System Check should always be used as the starting point for all powertrain diagnosis.

The Powertrain OBD System Check is an organized approach for identifying a problem. Driver comments normally fall into one of the following areas:

The diagnostic procedures used in this section are designed to find and repair powertrain related problems. The general approach is to find the appropriate diagnosis for a problem with five basic steps described below.

1. Understand the customers complaint. It is critical that the technician understand what the customers complaint is. Failure to understand this may lead to misdiagnosis, or unnecessary diagnosis. Among other things, the technician must know whether the condition is present at all times, only under certain circumstances, or truly intermittent (random). This will assist the technician in duplicating and diagnosing the problem. Another reason the technician must understand the customers complaint is so the technician may determine whether the complaint requires service or is normal vehicle operation. Trying to diagnose a complaint that is normal will waste time and may result in unnecessary service.
2. Are Diagnostics working properly? Use the Powertrain On Board Diagnostic (OBD) System Check. This is the starting point for the diagnostic procedure, always begin here.
3. Are DTCs displayed? If a DTC is identified by diagnostics, the Powertrain OBD System Check will direct you to the appropriate table.
4. Is the customers complaint related to a specific powertrain subsystem? If no related DTCs are set, the next quickest way to locate the problem is to narrow it down to a specific powertrain subsystem. If a specific subsystem can be pinpointed as the cause, it is easier to diagnose.
5. Is the problem powertrain related? Some customer complaints may appear to be powertrain related but are actually caused by other vehicle systems.

You must be familiar with some of the basics to use this section of the service manual. They will help you to follow diagnostic procedures in this section.

You should understand basic electricity and know the meaning of voltage (volts), current (amps), and resistance (ohms). You should understand what happens in a circuit with an open or a shorted wire and you should be able to identify a shorted or open circuit using a DMM.

You should be familiar with the DMM. You should be able to use the meter to measure voltage (volts), resistance (ohms), current (amps), capacitance (farads), intermittent (min/max), and frequency (Hertz).

You should only use a test lamp when a diagnostic procedure refers to a test lamps use. You should know how to use fused jumper wires to test components and allow DMM readings without damaging terminals. You should know how to use J 35616 connector test adapter kit. You should use the adapter kit whenever diagnostic procedures call for front probing any connector.

The PCM is designed to withstand normal current draws associated with vehicle operations, however, care must be used to avoid overloading any of these circuits. In testing for opens or shorts do not ground or apply voltage to any of the PCM circuits unless instructed to do so by the diagnostic procedures. These circuits should only be tested using the DMM.

Whenever a PCM removal and replacement is performed, follow the procedures in this section.

The electronic components used in the control systems are often designed in order to carry very low voltage. The electronic components are susceptible to damage caused by electrostatic discharge. Less than 100 volts of static electricity can cause damage to some electronic components. There are several ways for a person to become statically charged. The most common methods of charging are by friction and by induction. An example of charging by friction is a person sliding across a car seat. Charging by induction occurs when a person with well insulated shoes stands near a highly charged object and momentarily touches ground. Charges of the same polarity are drained off, leaving the person highly charged with the opposite polarity. Static charges can cause damage. Use care when handling and testing the electronic components.

Aftermarket (Add-on) Electrical and Vacuum Equipment is defined as any equipment installed on a vehicle after leaving the factory where the vehicle was originally assembled that connects, in any way, to the vehicles electrical or vacuum systems. These accessories may lead to an emission related OBD II failure while in use, but do not fail when the accessories are not in use. Refer to Checking Aftermarket Accessories in Wiring Systems. No allowances have been made in the design of this vehicle for this type of equipment. Therefore, the addition of aftermarket equipment must be done with the utmost care for the vehicle.

One of the most important tests is a visual/physical underhood inspection. This can often fix a problem. These quick tests take only a few minutes, can save valuable time, and help you correct the problem. For further information, refer to Visual/Physical Check in Symptoms .

All powertrain diagnosis should begin with a thorough visual inspection. Visual inspection can often lead to repair of a simple problem without use of the tables.

Refer to Power and Grounding Components in Wiring Systems.

When diagnosing this powertrain, you will almost certainly need to use the diagnostic procedures in this or other powertrain sections. The diagnostic procedures are mostly in the form of tables. At the beginning, formerly known as the Facing Page, of each DTC will be a circuit diagram, or a reference to a circuit diagram, a circuit description and notes about the condition or DTC diagnosed in the table. Reading the diagnostic support information will help you understand the system being tested, the components involved in the testing, how the PCM tests the system (enabling conditions), how the PCM determines that the diagnostic has failed (conditions for setting the DTC), and what the table is trying to accomplish. Below are explanations of the diagnostic support information and tables for DTCs.

The Circuit Diagram of the diagnostic support information page will show the circuits and components involved in setting the DTC. This diagram may be used as a reference when circuit tests are required in the table. If there is only a reference to a circuit diagram, or more detailed circuit information is required, the Engine Controls Schematics may be referenced.

The Circuit Description explains the sensor and/or circuits involved in setting the DTC. It also gives a brief description of when the DTC is set.

The running conditions, enabling conditions, are the conditions that must be met before the PCM will test the sensor/system. These conditions are generally set up so that the sensor/system may be reliably tested without a false failure indication.

The setting conditions are the conditions that must be met for the DTC to set. A sensor/system is tested only after the running conditions, described above, are met. If the enabling conditions are met, and the PCM detects an abnormal sensor/system condition, the appropriate DTC is set.

The actions taken are the steps the PCM takes after the DTC is set. These actions serve one of three purposes:

These are the conditions that must be met to turn OFF the MIL, and/or clear the DTC.

Diagnostic Aids provide helpful information when the conditions that caused the DTC or driveability problem is not currently present. Sometimes, with the help of snapshot on DTC set data, Freeze Frame or Failure Records, or information from the driver, the problem may still be identified or at least narrowed down to a short list of possible intermittent conditions. When this is true, the Diagnostic Aids may explain what to look for, and the most logical path to locate an intermittent condition.

The Test Descriptions are explanations of the reason certain tests are done, and what the test is supposed to uncover. The information is numbered according to the corresponding step in the diagnostic table. When questions of why a certain step is performed, or what results the step should actually produce, observe the step number next to the test you are performing. Refer to the information under Test Description that has the same number for an explanation.

Diagnostic tables are an organized and systematic approach to diagnosing a Diagnostic Trouble Code (DTC). The table consists of 5 separate columns: step number, action, value, yes, and no. The step number indicates which step is being performed. The action column contains all necessary information about how to perform a certain test. The last sentence in each action block will always be a question. The question can only be answered yes or no. The answer to the question will dictate which column you will go to next - yes or no. The yes or no answer to each test will lead to the next logical step within the diagnostic table. Most or the YES and NO boxes will take you to the next logical step within the table. However, some boxes may lead to other system diagnostics, or to the Diagnostic Aids when an intermittent condition exists.

Always begin with Step 1 at the top of the table unless there is a notice or caution above it. Never skip steps or jump ahead in the table unless specified by the Yes/No columns. Taking short cuts often leads to misdiagnosis. When a problem is found, make the necessary repairs, and then verify the repair.

Confident verification of a DTC repair can only be done by matching the test descriptions of the DTC and ensuring that the DTC RUNS and PASSES. To know if a test runs and passes use the scan tool and select DTC Status and note the DTC that needs verification. The status of the diagnostic test can now be observed. For symptom repairs, drive the vehicle and ensure the symptom is gone.

Many tables will have you testing terminal contact before replacing a component. This is done because the tests performed in tables can only test the continuity of a circuit across a wire or in-line connection, not the continuity across the connection at a component. Testing terminal contact will prevent the replacement of good components, prevent comebacks due to intermittent connection problems, and make some repair jobs easier, as in replacing a terminal instead of a component. For this reason it is very important to test the terminal contact when instructed to do so.

Testing terminal contact is easy as long as you have a supply of new terminals handy. The J-38125 Terminal Repair Kit, is a good source of terminals for testing terminal contact. It contains a supply of all currently used terminal series. To test terminal contact, start by inspecting the male terminals. They should be straight and aligned with other terminals in the row. They should not be twisted, bent or otherwise damaged. The female terminal should be, likewise, inspected for alignment and damage. Finally, take a new male terminal of the same series (e.g. Metri-pack 150, Weatherpack, etc.) and connect it to the female terminals to be tested. It should not fall out or be easily jarred out of connection. It should require some force to disconnect it. The force required to disconnect it will depend on the size of the terminal being tested. Larger terminals, Metri-pack series for example, should be very difficult to remove by hand. Smaller terminals, Micro-pack series for example, should be easier to disconnect by hand but still should not fall out. Replace, do not repair, any damaged terminals.

Diagnosing intermittent conditions can be difficult. The conditions that set the DTC set may not be present. This does not mean that the problem is fixed, it simply means that the problem intermittently occurs. The problem may return in the future. So, if at all possible, the problem should be diagnosed, and repaired. The only way to diagnose an intermittent condition is to gather information from the time when the DTC was set. This can be done in two ways; through snapshot data and driver observations. For further information refer to Scan Tool Snapshot Procedure .