Diagnose Functions - Overview

DIAGNOSE FUNCTIONS - OVERVIEW

General
The Engine Control Module (ECM) in itself diagnoses internal signals and functions, together with signals and functions from connected components.

Conditions for diagnosis
To start a diagnosis of a component or function, specific conditions must be fulfilled. The conditions for a diagnosis are different depending on which component or function being diagnosed. To be able to complete the diagnosis its driving cycle has to be performed. A driving cycle varies depending on which component or function being diagnosed.

Certain diagnoses only demand ignition on and ignition off in order to have a driving cycle performed. Other diagnoses demands several different conditions to be fulfilled, for example concerning:
- Vehicle speed
- Engine temperature
- Time passed after start
- Different load ratio and ratio of revolutions during the same driving
- A certain event (for instance the EVAP-valve is regulating).

When Engine Control Module (ECM) has performed all implemented diagnoses it is called the ECM has run a "trip". To run a "trip" it demanded long time driving during different working conditions. Also, it can be demanded the engine be off during a specific time and then be driven again.

Emission related diagnosis functions
The Engine Control Module (ECM) controls that the emission related systems are worked properly. These systems are controlled by performing a diagnose function. In the diagnose function the included components and the very system function are controlled.

Fault code memory
When the Engine Control Module (ECM) detects a fault the fault code with qualifier and status is stored in the fault code memory of the ECM. At certain fault codes the failed signal is replaced with a substitute value so the system is able to continue working.

If a fault is healed the fault code will be still in the fault code memory a time period, but the status on the fault code will change.

Lighting of Check engine lamp
At emission related fault codes when the fault code is set, even a counter is stored which counts down to determine when check engine lamp shall be lighted. The conditions of check engine lamp lighting vary depending on which fault cod is set.