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Alfa Romeo 159 Factory Service Manual (2005-2011)23 · Fault diagnosis
23 · Diagnostics

P0685 - main relay (unexpected intervention)

Make
Alfa Romeo
Model
159 Factory Service Manual
Year
2005–2011
Section
Examiner - diesel electronic management › P0685 - main relay (unexpected intervention)
Fault diagnosisP0685 - main relay (unexpected intervention)

P0685 - MAIN RELAY (UNEXPECTED INTERVENTION)

1.9 JTD 8V, 1.9 JTD 16V, 2.4 JTD 20V

The diagnostic equipment signals: Error P0685 (main relay), with detail "unexpected intervention"

This error is detected if the main relay switches off too quickly.

If the main relay switches off too quickly during a period of inactivity for the control unit, the fault codes will not be memorized.

0Preliminary checksALL OKPROBLEMS ENCOUNTEREDACTION

Select the following system on the diagnostic equipment: Diesel EDC16C39 electronic injection system.

Delete the errors present and press the START/STOP button.

Wait for the engine management control unit to switch off (min. 20 secs.).

Note: The main relay is switched off.

If the engine is very hot, the fans remain on after the ignition is switched off.

In this case, the control unit switches off automatically 10 secs after the fans are switched off.

Move on to Step 1
1Errors checkALL OKPROBLEMS ENCOUNTEREDACTION

Drive the vehicle in different driving conditions (engine speed and engine load) for a long stretch.

Listen out for any unusual noises and other system irregularities.

At the end of the road test, check that none of the following errors is present using the diagnostic equipment:

  • P0335 - Engine rpm sensor, with detail "signal not valid"
  • P0606 - Control unit broken (microprocessor)
  • P1618 – Control unit broken (HW CY940)
End of diagnosis1. The engine is not running smoothly

1. Proceed as instructed in the

See table D003 ENGINE NOT RUNNING SMOOTHLY / (IRREGULAR OPERATION)

2. The engine is losing power

2. Proceed as instructed in the

See table D004 ENGINE NOT RUNNING SMOOTHLY

3. The engine does not produce maximum performance

3. Proceed as instructed in the

See table D005 ENGINE DOES NOT PRODUCE BEST PERFORMANCE

4. The engine response is poor

4. Proceed as instructed in the

See table D016 POOR ENGINE RESPONSE

5. There is engine knock

5. Proceed as instructed in the

See table S003 ENGINE KNOCKING

6. Error P0335 is present

6. Proceed as instructed in the

See Test 1060GI ENGINE SPEED CHECK

7. Error P0606 is present

7. Proceed as instructed in the

See Test 1060GK CHECK CONTROL UNIT SOFTWARE AND HARDWARE

8. Error P1618 is present

8. Proceed as instructed in the

See Test 1060GL CHECK OPERATION OF MAIN ENGINE CONTROL UNIT RELAY

Parts & tools for this job For 2005 Alfa Romeo 159

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