Fault codes / actual values cannot be read out:
– With auxiliary heater switched off.
– If "AHE" system not recognized / not displayed:
Check fuse A1/F1, replace if necessary and switch on auxiliary heater.
Check whether diagnostic cable to auxiliary heater control unit is installed.
Check for short-circuit or open-circuit in diagnostic cable (to control unit, connection F1) or for defective plug connection.
If necessary, check whether control unit is able to diagnose (control unit 1569 only, part no. 000 446 02 29).
– If "switch on ignition" appears in HHT display when ignition switched on, check fuse terminal 15 (pin 2) of diagnostic socket.
– If fault code is displayed on vehicles with vehicle diagnosis system / flexible service system, diagnostic cable to display computer may be open-circuited.
– If HHT display remains dark:
Check fuse terminal 30 (pin 3) and ground connection (pin 1) of diagnostic socket.
On other vehicles check whether multiplexer is in order.
With this HHT display assignment of pin nos. 4 to 14 is possible, depending upon number of installed systems that can be diagnosed.
AHE Short test / system selection Commercial vehicle
Diagnostic socket contact
XX
System does not respond
Possible cause
- Diagnostic cable
- Control unit voltage supply
- Control unit