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STEP 3: Blink code identification and system response

  1. If you already know how to read ABS Blink Codes from the ECU in question, please go straight to STEP 4: Blink code list
  2. If you are unsure how to read ABS Blink Codes from the ECU, start by familiarising yourself with the diagram below, and then, where appropriate, follow the step by step procedure in the table
  3. Please ensure all necessary Health and Safety precautions are implemented before commencing any repair work

Knorr-Bremse A9 System ECU



System Response

Notes / Comments



ABS Warning Lamp Operation:

The warning lamp is triggered when the towing vehicle's ignition is switched on.



System O.K (system powered by ISO 7638 connection):

If no faults are detected during the static system test, the warning laamp goes out after approximately 1 second. After another two seconds, the warning lamp comes on again and remains on until the dynamic system test has been successfully completed without fault. The dynmaic system test involves driving the vehicle combination to aa speed in excess of approx. 12kmh.

Fault stored in ECU memory (system powered by ISO 7638 connection):

If a wheel speed sensor fault was stored before the system was last switched-off, the lamp does not go out again until the dynamic system test has been successfully completed without fault. The dynamic system test involves driving the vehicle combination to a speed in excess of approx. 12kmh. If the sensor fault still exists, or any other fault is detected the lamp will remain on. The ABS function of the ECU is switched off until the fault is corrected.

System powered by ISO 1185 (24N) - Stop Light Powering only:

The warning lamp is switched on when the brake light goes on (Stop Light Switch activated). The system test commences at thi isntant. In this case, the dynamic system test (see above) takes place immediately following the completion of the static system test. If faults are not detected, the warning lamp goes out one second after the switch is activated. In the case of a fault being detected, the warning lamp remains on. If following completion of the dynamic system test, the lamp fails to go out or lights up again before the ECU is switched off, the ECU has detected a fault. When a fault is detected, the ABS function is switched off.





Connect a Blink Code Adapter Switch (Part No. EZ1022) to the diagnostic socket 14, fitted as standard inside the ECU.



Blink Code display (i.e. a sequence of flashes) may be initiated.

In the absence of the Vehicle Manufacturer's Handbook, the Blink Codes can be obtained by short circuiting the two small contact pins on the terminal strip adjacent to the LED on the ECU. IMPORTANT: a time delay of at least 1 second after 'powering on' is required before shorting the pins. The pins must then be shorted for between 2 and 5 seconds in order to access the configuration and fault codes, which are displayed on the LED of the ECU.





Switch Ignition ON (ECU powered).

Wait for at least 1 second,

Then press the Diagnostic Push Button (on the Blink Code Adapter Switch) and hold for between 2 and 5 seconds, as shown in the diagram above,

Then release button.


The ABS Indicator Lamp will illuminate whilst the button is pressed, and go out when it is released.

The ECU will then transmit Blink Codes for any faults recorded on the ECU. The codes are displayed on the built-in LED in the Blink Code Adapter Switch, the LED built into the ECU, and the towing vehicle's dashboard warning lamp.

See the Blink Code List (and above diagram) for how to interpret the ABS Indicator Lamp flashes.



Count the flashes from the ABS Indicator Lamp.

Write down only the first 4 or 5 Blink Codes for faults recorded on the ECU (there may be several stored in the memory).

The first code displayed is for the configuration of the system (see above diagram), following which faults are shown as Blink Codes.





Turn Ignition OFF

Determine if faults recorded in III above are active or stored:





Active Faults: Will reappear (repeat) after any Blink Codes have been deleted from the ECU.

Stored Faults: Will be cleared when Blink Codes are deleted from ECU.

NOTE: Last fault stored is first fault displayed.




Clearing ECU fault memory:

Whilst pressing the Diagnostic Push Button, switch ignition ON, and hold button for a further 2 seconds.

Release button and the memory is cleared.

The ECU self-configures after the memory has been cleared.

The ECU self-configures to the status of the system at the time of ‘powering up’ and so any component connected after configuration has taken place will not be recognised by the ECU.





Turn Ignition OFF






Repeat steps II and III above.

Record Faults (Blink Codes).

Only active faults will be shown now.


To identify blink codes, refer to the Blink Code List. Make the necessary repairs to active faults. Repeat Step V (Clearing ECU fault memory), then road test the vehicle. The warning light should go out.

If the warning light remains after road testing, go back and repeat steps II , III and VII again until the warning light does go out.

Record faults for future reference

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