Important:  Understanding the table and using the table 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 any driveability and emissions system diagnoses. The Powertrain OBD System Check must always be the starting point for all powertrain system diagnoses. 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 any 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 this may lead to a misdiagnosis or an 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 will assist 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 operation. Trying to diagnose a complaint that is normal will waste 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 procedures. Always begin here.
3. Are any DTCs displayed? If a DTC is identified by the diagnostics, the Powertrain OBD System Check will direct you to the appropriate table.
4. Is the customer's complaint related to a specific powertrain subsystem? If no related DTCs are set, the quickest way to locate the problem is to narrow 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 actually caused by other vehicle systems.

You must be familiar with some of the basics to use this section of the Service Manual. These basics will 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. You should be able to use the DMM 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 J 35616 connector test adapter kit, 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 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 the vehicle leaves 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 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 diagnoses 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 the tables for the DTCs.

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

The circuit description explains the sensor and/or the circuits involved in setting the DTC. The circuit description 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 a 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 the conditions 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 3 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 malfunction indicator lamp (MIL) to turn off and for 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 present. Sometimes, with the help of the Snapshot, the Freeze Frame and 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 take 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 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.

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 column indicates which step is being performed. The Action column contains all the necessary information about how to perform a certain test. The last sentence in each Action Column cell 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 answer to each test will lead you to the next step to be performed or a particular action to take. Most Yes and No cells will have a Go to Step X statement. If a Yes or No cell does not have a Go to Step X statement, the actions performed in that Step will be the last for that table because the result 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 Step 1. 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 determine 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 an in-line connection, not the continuity across the connection at a component. Checking the terminal contact will prevent the replacement of good components, prevent comebacks due to intermittent connection problems, and make some repair jobs easier by replacing a terminal instead of a component. For this reason it is very important to check terminal contact when instructed to do so.

Checking the 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 checking terminal contact. The kit contains a supply of all of the currently used terminal series. To check the terminal contact, start by inspecting the male terminals. The terminals should be straight and aligned with all the 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 terminals to be checked. The male terminal should not fall out or be easily jarred out of connection. The male terminal should require some force to disconnect. The force required to disconnect the terminal will depend upon 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. For identification of terminal series and repair procedures, refer to the terminal repair kit and to Testing for Intermittent Conditions and Poor Connections in Wiring Systems .

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 present. This does not mean that the problem is fixed. The problem is likely to return in the future and 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 2 ways: through the Snapshot data and by driver observations.

The snapshot data, whether Freeze Frame and Failure Records or scan tool Snapshot, can be used to check data parameters to see if the parameters fall within a normal operating range. For example, a snapshot manifold absolute pressure (MAP) parameter value of 100 while the engine was idling is not normal, and would indicate that the MAP sensor voltage went high due to either 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 and causing an open circuit.

This kind of information, while not fool-proof, may be very helpful in diagnosing intermittent conditions, 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.