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→ Fitting location of EPC warning lamp
When the ignition is switched on the engine control unit tests all the components whose functions relate to the electronic throttle system.
The engine control unit activates the EPC warning lamp when the ignition is switched on. The warning lamp will go out soon after the engine starts, provided that the engine control unit does not detect any faults in the electronic throttle system and the activation of the lamp via the engine control unit is working properly.
If a fault is detected in the electronic throttle system while the engine is running, the engine control unit will activate the EPC warning lamp (see Fault Table for list of possible faults). At the same time a fault code is stored in the fault memory of the engine control unit.
Testing operation of warning lamp
Specification: the EPC warning lamp should light up
If the EPC warning lamp does not light up:
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‒ Test wiring from engine control unit to EPC warning lamp as follows:
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Problem:
EPC warning lamp is not activated or does not light up because of an open circuit.
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Remedy:
- Switch off ignition.
- Connect test box V.A.G 1598/31. Do not connect the engine control unit.
- Bridge sockets 1 and 48 on test box.
- Switch on ignition.
The EPC warning lamp should light up.
If the EPC warning lamp does not light up:
- Switch off ignition.
- Check whether lamp has burned out and test voltage supply to lamp
using current flow diagram.
If the warning lamp and the voltage supply are OK:
- Test for open circuit or short circuit in wiring between engine control unit
and EPC warning lamp using current flow diagram. Trace and eliminate fault.
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If there are no faults in the wiring to the EPC warning lamp:
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Cause of fault:
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Engine control unit defective =>Fit a new engine control unit =>Page 24-24.
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‒ Start the engine and allow it to run at idling speed.
Specification: the EPC warning lamp should go out soon after the engine starts
If the EPC warning lamp does not go out:
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‒ Interrogate fault memory of engine control unit.
If no faults are stored:
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Problem:
EPC warning lamp is activated
continuously because of a short
circuit to earth.
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Remedy:
- Switch off ignition.
- Connect test box V.A.G 1598/31. Do not connect the engine control unit.
- Measure resistance between vehicle earth and socket 48 on test box.
Specification: infinity (because the wire should not have any direct earth
connection)
If the reading does not match the specification:
- Trace and eliminate short circuit to earth in wiring between engine control
unit and EPC warning lamp using current flow diagram.
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If there are no faults in the wiring to the EPC warning lamp:
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Cause of fault:
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Engine control unit defective =>Fit a new engine control unit =>Page 24-24.
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