Using Flow Charts

When diagnosing the Northstar powertrain, you will almost certainly need to use the diagnostic procedures in this or other powertrain articles. These diagnostic procedures are mostly in the form of flow charts, because flow charts are generally the easiest type of diagnostic chart to follow. On each flow chart there will be a circuit diagram, descriptions and notes about the condition or code diagnosed in the flow chart. Reading these descriptions and notes will help you understand the code or condition and what the flow chart is trying to accomplish. Below are explanations of the information on the flow chart for diagnostic codes.

• Circuit Diagram
  
  The circuit diagram on the flow chart will show the circuits and components involved in setting the code. This diagram may be used as a reference when circuit checks are required in the flow chart. If more detailed circuit information is required, refer to CADILLAC -- ALLANTE SYSTEM WIRING DIAGRAMS article.
• Circuit Description
  
  The circuit description explains the sensor and/or circuits involved in setting the code. It also gives a brief description of when the code is set.
• Test Condition(s)
  
  The test 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.
• Failure Condition(s)
  
  The failure conditions are the conditions that must be met for the code to set. Failure conditions are checked only after the test conditions (described above) have been met. If they are true, then an input or system failure is present and the code is set.
• Action Taken
  
  The actions taken are the steps the PCM takes after the code 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.
• Notes
  
  The notes are explanations of the reason certain checks are done and what the check is supposed to uncover. The notes are numbered and correspond to the circled numbers on the flow chart. If you are performing a check and wonder why the check is being made or what the check is supposed to find, note the circled number next to the check you are performing. Refer to the note that has the same number for an explanation.
• Notes On Intermittents
  
  Most flow charts have one result which reads "Fault not present". This means that the conditions that were present when the code set are no longer there. Sometimes, with the help of PCM "SNAPSHOT" On Code Set  data 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 notes on intermittents will explain what to look for and which direction to head in looking for an intermittent failure.