Diagnostic Functions

Overview

General
The control module has an on-board diagnostic system (OBD). This system continuously monitors itself and its input and output signals.

Diagnostic trouble codes (DTCs)
If the control module detects a fault, it stores a diagnostic trouble code (DTC) and the ABS warning lamp lights. The exception is diagnostic trouble code (DTC) ABS-443 (battery voltage too low). The ABS warning lamp does not light if this diagnostic trouble code (DTC) is stored.
The most serious faults disengage the entire ABS system. Less serious faults do not affect the function of the ABS system. During disengagement, the control module stops all functions.
The ABS system does not operate normally if the ABS warning lamp is lit.
In the event of certain diagnostic trouble codes (DTCs), the control module carries out an immediate test when the ignition is switched on. This means that the ABS warning lamp remains lit, the fault remains and the ABS system will not function. For other diagnostic trouble codes (DTCs), the control module does not carry out diagnostic tests until the function is activated or vehicle speed exceeds 6 km/h. This means that the ABS warning lamp may go out as normal when the ignition is switched on or the engine is started, even though the fault remains.
At 6 km/h the control module tests the valves and pump motor.
If a fault disappears for any reason after the diagnostic trouble code (DTC) has been permanently stored in the control module, information about the fault remains in the control module.

Other
Every diagnostic trouble code (DTC) has a counter. The counter records the number of fault-free cycles since the diagnostic trouble code (DTC) was stored (intermittent fault). The counter determines whether the control module registers the diagnostic trouble code (DTC) as permanent or intermittent.
- When the counter is at 0, the control module has registered the fault as permanent.
- If the counter value is greater than 0, the control module registers the fault as intermittent. The counter is reset to 0 if the fault recurs.
- The diagnostic trouble code (DTC) and counter are erased when the counter reaches 200 (more than 199 cycles).