Inputs, Processing, and Outputs

Before any parts (such as a control module) are condemned as faulty, thorough investigation of all circuits connected to the control module should be performed. (If a system has self-diagnostic capabilities, this should be done if the troubleshooting for a specific fault is inconclusive.)

All electronically controlled systems should be approached with one rule in mind:

A control module will not produce the desired output if one or more of its inputs is impaired.

Consider a standard 4-pin relay:





When switch (S1) closes, the contacts should close and battery voltage should appear at terminal 87.


If any one of the inputs is impaired or missing, the desired output will also be impaired or missing. Since all inputs must be within nominal values at the control module (in this case, a relay), this is the point at which measurements are taken.



The same approach should be taken for all electronically controlled systems: verify that all inputs are present before replacing a control module. If a control module is producing the proper output (in the above example, battery voltage at pin 87) and the load is not operated, it is obvious that the load or the wiring between it and pin 87 is faulty. If all inputs are present, and no output is present at the control module, then and only then should the control module be replaced.







Important:
If a control module is determined to be defective, the printout from the Service Tester showing control module identification page, test codes, and all applicable troubleshooting must be attached to the control module being returned under warranty. The Technical Hotline contact number must be noted on the repair order and claim.

In all cases, verify proper voltage level at all power inputs, and check all grounds by measuring voltage drop. Depending on the type of input, other signals (e.g., A.C. voltage, frequency, etc.) may have to be verified. Refer to the appropriate diagnostic manual for this information.