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STEP 3: Blink code identification and system response

  1. The AL4T does not use Blink Codes. Any fault detected by the unit will be displayed on the side of the ECU housing by a combination of LEDs (see diagram below)
  2. To understand how to interpret the diagnostic displays, refer to the detailed explanations provided in the table below
  3. Please ensure all necessary Health and Safety precautions are implemented before commencing any repair work

Knorr-Bremse AL4T System ECU

Step

Action

System Response

Notes / Comments

I

 

Establishing whether any faults are present.

 

 

The AL4T System has a built-in Diagnostics Display on the side of the ECU housing (see above Diagram) with one green and five red LEDs.

Any fault detected by the ECU will be shown on the Diagnostics Display as well as being signalled by the illumination of the Trailer Headboard Warning Lamp.

When a fault is indicated, it is good practice to reset the display to ensure that the fault is still present. This is done by passing a magnet closely across the word "RESET" on the face of the display window (a wheel Speed Sensor can be used as the magnet).

If resetting is successful, then all LEDs in the display will illuminate.

After resetting, if a fault is still present, then the Diagnostics Display will show the nature of the fault.

 

II

 

 

 

System O.K.

If the Headboard Warning Lamp is illuminated, then check the Warning Lamp Circuit.

III

 

 

 

No power

Check supply. If O.K. then the ECU has failed. The ECU of the AL4T unit is no longer available, therefore, if a failure occurs, the sytem must be replaced with a Conversion Kit, Part No. KB4T.

IV

 

 

 

ECU failure

The ECU of the AL4T unit is no longer available, therefore, if a failure occurs, the sytem must be replaced with a Conversion Kit, Part No. KB4T.

V

 

 

Sensor 1 (left) failure

Unplug Sensor and measure resistance (1.5 to 2.5 Kilo Ohms). If O.K. the measure across harness. If harness is O.K. the ECU failure (see IV above).

VI

 

 

Sensor 2 (right) failure

Unplug Sensor and measure resistance (1.5 to 2.5 Kilo Ohms). If O.K. the measure across harness. If harness is O.K. the ECU failure (see IV above).

VII

 

 

Modulator failure

Remove ECU from top of valve by removing the 4 fixing screws, Check plugs are correctly aligned. Measure resistance across yellow wires (40-50 Ohms). Measure resistance across blue wires (40-50 Ohms). Measure resistance across blue and yellow wires (1 Mega Ohm minimum). If all readings are acceptable then the ECU has failed (see IV above).

VIII

 

 

Incorrect voltage

Check that power supply is between 18 and 32 Volts. If voltage O.K. then the ECU has failed (see IV above).

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