Before changing a control module
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Before changing a control module
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When all checks have been carried out as described in the diagnostic procedure for each diagnostic trouble code or through manual fault diagnosis without any fault coming to light, it is natural to assume that the control module is defective. Bearing in mind the fact that the control module is a very expensive high-quality component, it is important to be as sure as possible that your diagnosis is correct. Go through the following points very carefully before you definitely decide that the ACC control module is the cause of the fault.
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1.
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Check once again that all points in the diagnostic proocedure for the relevant trouble code have been carried out.
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2.
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Study the wiring diagram of the circuit in question and make sure you understand how it works. If necessary, refer to appropriate parts of the technical description and the description of electrical functions in Service Manual 3:2 "Electrical system, wiring diagrams".
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3.
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Check all grounding points. If you have already done this, do it again. Check that power ground and signal ground are physically and electrically separate from each other.
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4.
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Check the power supply for the control module.
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5.
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Go through the points under
once again.
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6.
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If the original fault persists in spite of this, change the ACC control module.
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