Diagnostic Functions ME7: Overview

Overview

Overview
The engine control module (ECM) checks itself and all input and output signals.

Four different conditions for diagnostics

Trip
When all diagnostic functions have been gone through.

Drive cycle
Begins 15 seconds after the engine starts and finishes when the engine is switched off.

Warm-up cycle
Begins when the engine starts and engine coolant temperature (ECT) is below 40°C (104°F) and finishes when the engine temperature is above 84°C (183.2°F).

Time
Some diagnostics are carried out a set amount of time after a particular occurrence (for example when vehicle speed is above 23 km/h (14.3 mph)).

Emissions related diagnostic functions
The engine control module (ECM) checks that the emissions related functions are working. These systems are checked by an ongoing diagnostic function. The diagnostic function checks that the relevant components and the actual function in the system are working. It is called a trip when all diagnostic functions have been gone through. Trip time may vary depending on driving style, but normally it takes approximately 25 minutes fir mixed driving.

Diagnostic trouble code (DTC) memory
When the engine control module (ECM) detects a fault, the diagnostic trouble code (DTC) is stored with the qualifier and status in the unit DTC memory. For certain types of diagnostic trouble codes (DTCs) the missing signal is replaced with a substitute value so that the system can continue to operate.
If the fault disappears, the diagnostic trouble code (DTC) will be present for a longer time in the diagnostic trouble code (DTC) memory although the status of the code will have changed.

Malfunction indicator lamp (MIL) activation
Emissions related diagnostic trouble codes (DTC) are stored even when it is lit. A counter counts down to determine when the malfunction indicator lamp (MIL) should be lit. The conditions for lighting the malfunction indicator lamp (MIL) vary depending on the diagnostic trouble code (DTC) that is stored.
Faults that have been diagnosed in the automatic transmission may affect emissions and the automatic transmission may request the activation of the malfunction indicator lamp (MIL).