Important:  Understanding the table and using the table correctly reduces diagnostic time, and prevents the unnecessary replacement of parts.

After the visual and physical inspection is complete, the Powertrain OBD System Check should be performed. The Powertrain OBD System Check provides 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 any powertrain diagnosis.

The Powertrain OBD System Check is an organized approach to 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 the 5 basic steps described below.

1. Understand the customer's complaint. It is critical that the technician understand what the customer's complaint is. Failure to understand the complaint 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. This assists the technician in duplicating and diagnosing the problem. Another reason the technician must understand the customer's complaint is so the technician may determine whether the complaint requires service or is a normal vehicle condition. Trying to diagnose a complaint that is normal wastes time and may result in unnecessary service.
2. Are the diagnostics working properly? Use the Powertrain OBD System Check. This is the starting point for the diagnostic procedure. Always begin with the Powertrain OBD System Check.
3. Are DTCs displayed? If a DTC is identified by diagnostics, the Powertrain OBD System Check directs you to the appropriate table.
4. Is the customer's complaint related to a specific powertrain subsystem? If no related DTCs are set, the next quickest way to locate the problem is to narrow the the problem down to a specific powertrain subsystem. If a specific subsystem can be pinpointed as the cause, the problem 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 basic information and procedures in order to use this section of the service manual. These basics help you to follow the 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 digital multimeter (DMM). You should be able to read and understand a wiring diagram.

You should be familiar with the DMM, particularly the essential tool J 39200 , the digital multimeter. You should be able to use the multimeter to measure voltage (volts), resistance (ohms), current (amps), capacitance (farads), intermittents (min/max) and frequency (hertz).

You should only use a test lamp when a diagnostic procedure refers to test lamp 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 the connector test adapter kit, J 35616 and use the kit whenever diagnostic procedures call for front probing any connector.

The PCM is designed to withstand the 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 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 static charging are by friction and by induction. An example of charging by friction is 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 vehicle's electrical or vacuum systems. No allowances have been made in the design of this vehicle for this type of equipment. Therefore, addition of aftermarket equipment must be done with the utmost care for the vehicle.

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

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 is a circuit diagram, descriptions, and notes about the condition or the DTC diagnosed in the table. Reading the diagnostic support information helps you to understand the system being tested, the components involved in the testing, how the PCM tests the system, how the PCM determines that the diagnostic has failed, and what the table is trying to accomplish. Below are explanations of the diagnostic support information and the tables for DTCs.

The circuit diagram of the diagnostic support information page will show the circuits and the components involved in setting the DTC. This diagram may be used as a reference when circuit checks are required in the table. If more detailed circuit information is required, use the Engine Controls electrical schematics.

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

The running conditions are the conditions that must be met before the PCM tests the sensor or system. These conditions are generally set up so that the sensor or system may be reliably checked without a false failure indication.

The setting conditions are the conditions that must be met for the DTC to set. A sensor or system is checked only after the running conditions are met. If the enabling conditions are met, and the PCM detects an abnormal sensor or 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 3 purposes:

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

The Diagnostic Aids provide helpful information when the conditions that caused the DTC or driveability problem are not currently present. Sometimes, with the help of the Freeze Frame or Failure Records, or information from the driver, the problem may still be identified or 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 checks are done, and what the check is supposed to accomplish. The information is numbered according to the corresponding step in the diagnostic table. When a question of why a certain step is performed, or what results the step should actually produce, observe the step number next to the check you are performing. Refer to the information under Test Description that has the same number for an explanation.

The 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 information necessary to perform a certain test. The last sentence in each action block always asks a question. The question can only be answered yes or no. The answer to the question dictates which column to go to next - yes or no. The yes or no answer to each test leads to the next logical step within the diagnostic table. Most of the YES and NO boxes 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. 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 test runs and passes. To know if a test runs and passes use the scan tool, select DTC Status, and note the DTC that needs verification. The status of the diagnostic test can be now observed. For symptom repairs, drive the vehicle and ensure the symptom is gone.

Many tables direct you to check terminal contact before replacing a component. This is done because the checks performed in tables can only check the continuity of a circuit across a wire or in-line connection, not the continuity across the connection at a component. Checking terminal contact prevents the replacement of good components, prevents returns due to intermittent connection problems, and makes some repair jobs easier, as in replacing a terminal instead of a component. For this reason it is very important to check terminal contact when instructed to do so.

Checking terminal contact is easy if you have a supply of new terminals handy. The J 37027-A is a good source of terminals for checking terminal contact. The kit contains a supply of all currently used terminal series and also has the male terminals (12047581) and female terminals (12052922) necessary to build the diagnostic jumper for ignition control DTC diagnosis. For the connector part number, refer to the Wiring Systems section of Body and Accessories. To check terminal contact, start by inspecting the male terminals. The terminals should be straight and aligned with other terminals in the row. The terminals should not be twisted, bent, or otherwise damaged. The female terminal should also be inspected for alignment and damage. Finally, take a new male terminal of the same series (e.g. Metripack 150, Weatherpack, etc.) and connect the male terminal to the female terminal to be checked. The terminal should not fall out or be easily jarred out of the connection. Some force should be required to disconnect the terminal. The force required to disconnect the terminal depends on the size of the terminal being checked. Larger terminals, the Metripack 630 series for example, should be very difficult to remove by hand. Smaller terminals, the Micropack series for example, should be easier to disconnect by hand but still should not fall out. Replace, do not repair, any damaged terminals. Refer to Connector Repairs in Wiring Systems and the terminal repair kit for identification of terminal series and for the repair procedures.

Diagnosing intermittent conditions can be difficult. The conditions that set a DTC set may not be present. This does not mean that the problem is fixed, but that the problem occurs intermittently. The problem may return in the future. 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 2 ways: through snapshot data or by driver observations. For further information, refer to Symptoms .