Powertrain Control Module Diagnosis

POWERTRAIN CONTROL MODULE DIAGNOSIS

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 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 DTCs.

Circuit Diagram

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 checks are required in the table. If more detailed circuit information is required, the Engine Controls Electrical Schematic Diagrams may be referenced.

Circuit Description

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.

Conditions for Running the DTC

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.

Conditions for Setting the DTC

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.

Action Taken When The DTC Sets

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

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

Conditions For Clearing The MIL/DTC

These are the conditions that must be met for the Malfunction Indicator Lamp (MIL) to go OFF and/or the DTC to clear.

Diagnostic Aids

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

Test Description

The Test Description are explanations of the reason certain checks are done and what the check is supposed to uncover. This information is numbered and corresponds to the steps on the table. If you are performing a check and wonder why the check is being made or what the check is supposed to find, 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.

Diagnostic Table

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.