On-demand tests allow immediate diagnostics of car problems, bypassing the need for lengthy drive cycles and pending codes. These tests, accessible through a scan tool, help pinpoint issues within the Powertrain Control Module (PCM) and other car modules. Let’s explore the two main types of PCM on-demand self-tests: Key On Engine Off (KOEO) and Key On Engine Running (KOER).
Key On Engine Off (KOEO) Self-Test
The KOEO test checks the functionality of the PCM with the ignition on and the engine off. This test analyzes specific sensor and actuator circuits. Crucially, the problem must exist during the test for the KOEO to identify it. If an issue is detected, a Diagnostic Trouble Code (DTC) is transmitted via the data link to the scan tool.
Key On Engine Running (KOER) Self-Test
The KOER test, performed with the engine running and the vehicle stationary, assesses PCM functionality under operating conditions and normal temperature. This test evaluates various inputs and outputs, including brake pedal position, transmission control, and power steering, if applicable. Similar to the KOEO test, the issue must be present during testing for the KOER to detect it, generating a DTC upon detection.
Module-Specific Tests
Beyond PCM tests, on-demand tests exist for other modules, revealing any existing hard faults. For instance, an instrument cluster test might trigger a gauge sweep, illuminate all warning lights, and activate audible alerts.
When to Use On-Demand Tests
While harmless to run anytime, these tests prove particularly useful after component replacements or repairs. For example, after replacing an ABS module, running a test confirms its proper function and communication. Similarly, after an engine or transmission swap, these tests verify correct connections, preventing future check engine light issues.
alt text: a mechanic working on a car engine using a diagnostic tool
Conclusion
On-demand self-tests offer a powerful diagnostic tool for identifying car problems, especially after repairs or modifications. Understanding the KOEO and KOER tests, along with module-specific tests, empowers car owners and technicians to quickly pinpoint and address issues, preventing potential complications down the road. These tests are designed with dealer technicians in mind, providing efficient troubleshooting capabilities.
