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

After the visual inspection is complete, the Powertrain OBD System Check should be performed. The Powertrain OBD System Check is designed as a Master table for driveability and emissions system diagnosis. The Powertrain OBD System Check must always be the starting point for all powertrain system diagnosis. The Powertrain OBD System Check provides a logical step by step process for diagnosing 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 OBD System Check. This is the starting point for the diagnostic procedures, 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 DTC(s) 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 able to read and understand a wiring diagram.

You should be familiar with the Digital Multimeter (DMM), particularly essential tool J 39200. You should be able to use the meter 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 it's 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 Connector Test Adapter Kit, J 35616 and use it 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 Digital Multimeter J 39200.

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. 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 underhood inspection. This can often fix a problem. These quick tests take only a few minutes, can save you valuable time, and help you repair the problem.

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. These 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, descriptions and notes about the condition or DTC diagnosed in the table. Reading this Diagnostic Support Information will help you understand the DTC or condition and what the table is trying to accomplish. Below are explanations of the diagnostic support information and tables for DTC(s).

The circuit diagram shows the circuits and 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, refer to the Engine Controls Schematics.

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 are the conditions that must be met before the PCM will test for a failure. These conditions are generally set up so that an input or system may be reliably checked and not give a false failure indication.

The setting conditions are the conditions that must be met for the DTC to set. A failure condition is checked for only after the running conditions (described above) have been met. If they are true, then an input or system failure is present and the DTC is set.

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

1. To inform the driver of the problem.
2. To preserve the driveability of the vehicle.
3. To prevent the failure from causing any damage to the vehicle.

These are the conditions that must be met for the MIL to go Off and / or the DTC to clear.

Most tables have one result which reads Fault not present. This means that the conditions that were present when the DTC set are no longer there. 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 failures. When this is true, the Diagnostic Aids may explain what to look for and which direction to head in looking for an intermittent failure

The Test Descriptions may include explanations of the reason certain checks are done, what the check is supposed to uncover and/or additional information. This information is numbered and corresponds to the steps on the table. If additional information is available on a particular step, the step number will be italicized. 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 five 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 you to the next step to be performed or a particular action to take. Most boxes will have a Go to Step X statement. If a yes or no block does not have a Go to Step X statement, the text inside will be the last step taken on the table because it will either be a solution or a Fault not present condition.

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 conditions 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 be now observed. For symptom repairs, drive the vehicle and ensure the symptom is gone. Some system diagnostic tests can be performed using the Service Bay Test function of the scan tool. A Service Bay Test will allow a diagnostic test to run under static conditions such as in a service area.

Many tables will have you checking 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 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 check terminal contact when instructed to do so.

Checking terminal contact is easy as long as you have a supply of new terminals handy. The Terminal Repair Kit, J 38125, is a good source of terminals for checking terminal contact. It contains a supply of all currently used terminal series. To check 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. Metripack 150, Weatherpack, etc.) and connect it to the female terminal(s) to be checked. 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 checked. Larger terminals, Metripack 630 series for example, should be very difficult to remove by hand. Smaller terminals, 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 Intermittents and Poor Connections Diagnosis and the Terminal Repair Kit, J  38125, for identification of terminal series and repair procedures.

Most tables have one result which reads The Problem Is Intermittent. This means that the conditions that were present when the DTC set are no longer there. This does not mean that the problem is fixed, it simply means that the problem was present but is not present now. The problem is likely to return in the future so it should be diagnosed and repaired if at all possible. The only way to diagnose a problem that is not present 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.

Snapshot data whether Freeze Frame, Failure Records or scan tool snapshot, can be used to check data parameters to see if they fall within normal operating range. For example, a snapshot MAP parameter value of 100 while the engine was idling is not normal and would indicate that the MAP sensor voltage went high either due to an open in the 5 volt return or a short to voltage on the sensor signal circuit. Driver observations may give additional information about the system or area of the car that should be checked for an intermittent. For example, while diagnosing an intermittent DTC P0403, you find out the driver noticed that the MIL only comes on after an extended wide open throttle maneuver. This would lead you to check the wiring harness that carries the EGR control circuit underhood, because it is possible that powertrain movement (during WOT) is stretching the harness, causing an open circuit.

This kind of information, while not airtight, may be very helpful in diagnosing intermittent conditions. Besides, it may be the only information you can get about a failure and the only chance to find the cause of an intermittent. Refer to Intermittent Conditions in Symptoms, for more information.