Engine Control Module

The multi-pin harness connectors of Engine Control Module (ECM) are equipped with a protective housing secured by a locking mechanism and shear bolts -arrows-. Also to impede removing of the shear bolts, their threads are coated with locking compound.

Fig 1: Locking Mechanism And Shear Bolts

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The protective housing must be removed so that multi-pin harness connectors can be disconnected from Engine Control Module (ECM), e.g. to connect the test box or to replace the ECM.

Special tools and workshop equipment required

Hot air gun (from wiring harness repair kit VAS 1978)
Attachment nozzle (from wiring harness repair kit VAS 1978)
Locking pliers (commercially available)

Removing

-- Turn ignition and remove ignition key.

-- Pry off caps on wiper arms using a screwdriver.

-- Loosen nuts -arrows- by several turns.

Fig 2: Identifying Wiper Arm Nuts

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-- Loosen wiper arms by gently rocking wiper arm. Remove nuts and remove wiper arms.

-- Unclip spray nozzles -arrow-.

Fig 3: Removing Spray Nozzle

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-- Push spray nozzle with lines still attached back through opening and into plenum chamber.

-- Remove rubber seal -1- for plenum chamber cover.

Fig 4: Plenum Chamber Cover And Rubber Seal

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-- Remove plenum chamber cover -2-.

CAUTION:

To avoid damage (burning) of wire connections and harness connectors, insulation and control modules, the following work steps must be adhered to exactly! Observe operating instructions for heat gun.

-- Adjust settings on hot air gun as depicted in the illustration, this means potentiometer -2- for temperature setting at maximum heat output and two-stage switch -3- for air quantity at position "3".

Fig 5: Identifying Controls For Temperature Adjustment And Air Quantity

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NOTE:

Next, the thread of protective housing in which the shear bolts is threaded in is heated using the heat gun. This step decreases the locking effect of the locking compound on the thread of the shear bolts, thus allowing the shear bolts to be removed more easily.

Cover all painted parts to prevent damage from the hot air gun or locking pliers.

WARNING:

By heating the shear bolts, parts of the protective housing are heated intensely. Do not burn yourself on this! Make sure that only the shear bolt is heated if possible and no other components in the vicinity are heated. Possibly cover these parts.

-- Perform the following work steps in succession at both shear bolts -arrows-.

Fig 6: Locking Mechanism And Shear Bolts

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-- Guide nozzle of hot air gun on to shear bolt of protective housing.

-- Switch heat gun on and heat bolt for approximately 20 to 25 seconds.

-- Then grasp bolt head using locking pliers and remove shear bolt.

-- Remove protective housing.

-- Disengage and disconnect front multi-pin harness connector -2- of Engine Control Module (ECM)..

Fig 7: Disengaging/Disconnecting Front Multi-Pin Harness Connector Of Engine Control Module (ECM) & Securing Clip

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-- Disengage securing clip -arrow-.

-- Remove Engine Control Module (ECM) -1- from bracket.

-- Disengage and disconnect rear multi-pin harness connector of Engine Control Module (ECM).

NOTE:

Adaptation values are erased when connectors are disconnected from the Engine Control Module (ECM), DTC memory content remains intact.

Installing

Installation is in reverse order of removal, noting the following:

-- Re-equip Engine Control Module (ECM) with the protective housing.

-- Clean threaded holes for shear bolts of locking compound residue. Cleaning can be performed with a thread cutter (tap).

-- Use new shear bolts.

After installing a new Engine Control Module (ECM), the following work steps must be performed:

-- Activate Engine Control Module (ECM) in "Guided Fault Finding" under diagnostic object "Engine Control Module (ECM), replacing" .