Maintenance manual for sunray hfc4da1-2c china-IV diesel engines
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19.
DTC P0686 The main relay opens too early.
P0687 The main relay opens too late.
Fault Description: With the ignition switch OFF, the input circuit of main relay through K47 is actuated by V3 and
ECU Pin K46 and the electromagnet picks up the contact of output circuit, so the output circuit of main relay is in
continuity. Then, the power supply into the internal control module via ECU Pin K01, K03 and K05. If the ECU
signal for relay control is distorted, DTC shall be generated.
Diagnosis Hint: The intermittent failure may be caused by poor contact, abrasion of wire insulation or breakage of
the wire inside insulation. The ignition 1 relay fault shall lead to the failed starting of engine, for there is no voltage in
the ignition coil or fuel injectors in electronic ignition system and they cannot work without being electrified.
Terminal ECU
K47 Main relay control signal
Main relay
Power supply of main relay
Power supply of ignition switch
Control of main relay
Ignition
switch
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