R 486

Without the shunt resistor the field current would only be 80 mA — much too little to reliably excite the alternator. 28

Testing

Note the following points before checking the alternator circuit.

1. Battery fully charged, electrolyte level o. k., battery connections o. k.?

2. Drive belt correctly tensioned, no damage?

3. Does charge indicator lamp light up when ignition is switched on?

You require a voltmeter, ammeter and an oscilloscope for accurate testing.

A) Regulating voltage

Connect voltmeter to D + /61 and ground (earth). Switch on ignition: specified value = 1.4 — 2.0 Volt Start engine: specified value = 13.2 — 14.2 Volt

Switch on loads (main beam, fresh air blower 4, rear window heater): specified value = 13.2 - 14.2 at approx. 2,000 rpm

B) Charging current

Connect ammeter to battery negative pole (inductive clip).

Switch on loads (as above), measure current.

Start engine, set engine speed to approx. 2,000 rpm.

The ammeter must indicate a definite charge (> load current)

C) Oscilloscope

Connect oscilloscope to D + /61 (use special oscilloscope input). Set engine to 2,000 rpm and switch on loads (as above).

The scope screen must show a uniform current wave trace without any dips or excessive current peaks. The alternator must be warm for this test.

Your exercises

1. Check the field current circuit a) with a test lamp b) with a voltmeter

Write down your testing points and the values!

2. Check the charging current.

Please write down all the measured values!

3. Connect up the oscilloscope What do you see on the screen? Disconnect D + /61, restart the engine. What do you see on the screen?

The central electronic warning system, i.e. central warning, is located on the left of the driver's foot well behind the clutch foot rest. The electronic warning system automatically monitors various functions in the vehicle and signals a fault in the components monitored, depending on priority, by flashing or illuminating the central warning lamp or the appropriate warning indicator in the combination instrument. From Model 79 the acknowledge button in the center console lights up along with the central warning lamp.

The control function of the central warning light system is divided into two major groups:

Group "A" - engine oil pressure

- engine oil level

- brake circuit (pressure) failure*

- brake fluid level

Any of these malfunctions reported by the system must be corrected Immediately.

Group "B" - Brake wear (pads) indicator

- parking brake

- coolant level

- fuel reserve level

- windshield and headlight washer fluid level

- stop lamps

- tail lamps

- toothed belt tensioning

- ABS (antilock system) Any group "B" malfunction reported by the system should be corrected as soon as possible.

'discontinued Iram Mod. 64 "new from Mod. 86

A) Function

When the ignition is switched on, all warning indicators (indicator lamps and lettering) as well as the central warning lamp and the lamp test acknowledge button light up. The lamp test of items 1 — 10 and 12 — 14 goes off when the engine is started and that of item 11 after the first brake application.

The readiness to indicate in the case of a fault at item 1 begins approx. 2 sec. after the engine starts, at item 2 when the ignition is switched on and the engine is stationary and at all other items when the engine is running. If there is a fault at item 1—4, the central warning lamp and the appropriate individual warning indicator flash on and cannot be cancelled by pressing the acknowledge button. Item 3 is stored and automatically flashes again even after a break in the journey. Item 3 can only be cancelled by briefly diconnecting one pole of the battery.

The other stores, items 4and 5, are cancelled when the ignition is switched off. A fault at item 5—16 is indicated by the central warning lamp and the appropriate individual warning indicator glowing all the time. The central warning lamp of items 5 and 7—14 can be cancelled by pressing the acknowledge button in the center console, but the individual warning indicator continues to glow. When the handbrake, item 6, is applied, the warning lamps can be cancelled by releasing the handbrake.

Example:

Item 9 tank reserve - fuel reserve level is reached while driving. All lamps light up to test their function when the ignition is switched on. When the engine is started and if the fuel reserve level has not yet been reached, the central warning lamp, acknowledge button and the fuel reserve warning lamp go off. If the fuel reserve level has been reached, i. e. the fuel level float closes the reserve indicator contact, the central warning lamp /acknowledge button and the fuel reserve warning lamp will light up 10 seconds after the contact closes. When the acknowledge button is pressed (driver has noticed reserve warning), only the central warning lamp and the acknowledge button go off; the warning lamp continues to glow until the tank has been topped up as necessary. The time lag of 10 seconds for the indicator in the example (items 4, 7, 10 after 20 sec.) was chosen to ensure that the warning indicator does not respond during cornering, i. e. as a result of the change in fuel level.

Central warning from Model 84

The construction and the functions of the central warning were changed from Model 84. The whole electronic circuit was revised and laid out to accommodate futrue monitoring functions. It was possible to reduce the size of the central warning by about 50% at the same time. The new central warning may only be installed in vehicles from Model 84 onwards.

The changes:

The connector assignment was changed in some terminal connections.

The warning lamps are extinguished by the alternator charge, terminal 61 — and not by the start pulse, terminal 50.

The "brake circuit" warning lamp is deleted. The brake circuit is monitored by way of the brake fluid level.

Vehicles with the ABS system are equipped with an ABS warning lamp which is tripped directly by the ABS control unit — via the central warning. In the event of a fault the central warning now switches on the central warning lamp as well.

In addition to the transmitter, the coolant level is monitored by a pressure switch installed in the coolant expansion line, (see page 36)

Bulb Monitoring Unit

The bulb monitoring unit (behind CEB) has been revised. The monitoring of electric power for the tail lights is now accomplished with electronic components and no longer with mechanical reed switches. The new bulb tester (928.641.603.04} is fully interchangeable with earlier models.

Testing

The central warning has a color-coded black and yellow, 25-pole connector strip which is connected to the instrument wiring harness. The connectors cannot be connected the wrong way round.

up to Model 83 from Model 84

All the items monitored in the vehicle can be checked in order to test operation of the warning system.

Lamp test

Switch on the ignition to check whether all warning lamps (WL), the central warning lamp (ZW) in the combination instrument and the acknowledge button in the center console light up.

If one of the lamps does not glow, first check the condition of the bulb or its wiring.

Start the engine, release the handbrake and press the brake pedal once - ail the warning lamps must go off. (Then switch off the ignition.)

Operational test

I. Up to Model 83, the warning lamps are extinguished by the engine cranking pulse (terminal 50). Accordingly, it is necessary to crank the engine, without letting it run, in order to switch off the warning iamps.

To do this, pull the HT lead, terminal 4, off the distributor and apply it to ground (earth) {screw heads on crossbar mounting),

II. From Model 84, the warning lamps are no longer extinguished by the cranking pulse, but by the voltage rise of the alternator, terminal D +/61.

The switching threshold is in the region of > 6 V, i.e. when the engine starts and if the alternator charging circuit is in order (voltage rise >6 V), the warning lamps are extinguished. This means that, even when there is a break at D +/61, the warning lamps go off immediately the ignition is switched on because terminal 15 (+) is applied to the central indicator via the charge indicator lamp. In order to switch off the warning lamps to test them, it is necessary to separate the multipoint engine connector in the engine compartment after switching on the ignition (lamp test), Connect terminal 1 on connector (front wiring harness) to B+. The warning system,with the exception of oil level and oil pressure, can now be tested, ZW — central warning lamp ZW — central warning lamp WL — warning lamp / warning lettering

Q — acknowledge button (in center console) — functions together with ZW from Mod. 79.

1. Brake light

Operate foot brake.

- Brake light WL must go off.

2. Handbrake

Apply handbrake (or connect cable on handbrake contact to ground)

- Handbrake WL, ZW and Q must light up. The two lamps go oft only when the handbrake is released.

3. Coolant temperature

Pull cable connector terminal W (smaller connector lug) off the temperature transmitter on the engine and connect it to ground.

- Coolant temperature WL, ZW and Q must light up. Press acknowledge button, ZW and Q go off, WL must continue to glow. The WL goes off when the ground connection is removed.

4. Oil level up to Model 83

The transmitter is fitted on the front of the oil sump. Pull cable off transmitter and hold it against ground, or additionally connect multipoint connector part of front wiring harness terminal 6 to ground and attach the connector.

- Oil level WL, ZW and Q must flash. Press acknowledge button, all lamps must continue flashing. All lamps must go off when the cable is attached to the transmitter, or when the ground connection is removed.

4a. Oil level from Model 84

Connect connector P3 (M23 model 85 and later) on CEBto ground (connector remains plugged in).

- Oil level WL, ZW and Q must flash Press acknowledge button, all iamps must continue flashing. All lamps must go off when the cable is attached to the transmitter, or when the ground connection is removed.

5. Oil pressure up to Model 83

Separate multipoint engine connector. Use auxiliary cable to apply connector part of front wiring harness, connector socket No. 2, to ground.

— Oil pressure WL, ZW and Q must flash after about 2 seconds. Press acknowledge button, all lamps must continue flashing. The lamps must go off when the auxiliary cable is removed.

Sa. Oil Pressure from Model 84

Connect connector P2 (M22 model '85 and later) on CEB to ground {connector remains plugged in).

— Oil pressure WL, ZW, and Q must flash after about 2 seconds. Press acknowledge button, all lamps must continue flashing. The lamps must go off when the auxiliary cable is removed.

6. Brake lining wear

Separate one plug connection of a lining contact segment. (Front left-hand side of engine compartment at level of brake master cylinder.)

— Brake lining WL, ZW and Q must light up. Press acknowledge button — ZW and Q go off, WL continues to glow. Reconnect plug connection, WL continues to glow.

Note: Allow the individual warning lamps (WL) to continue glowing in the following tests until you have checked through all items — otherwise you will have to keep repeating the procedure as per Section I or II.

7. Coolant level

The transmitter (float) is located inside the coolant expansion tank. Pull off cable and join the cable's plug connections together.

— Coolant level WL, ZW and Q must light up after about 20 seconds. Press acknowledge button, ZW and Q go off and WL must continue glowing. The WL continues to glow after the cable bridge is disconnected.

7 a. Coolant level from Model 84

Trip warning as described under 7. Press acknowledge button so that only the WL glows. Fit hand pump VW 1274 on coolant filler neck and pressurize cooling system to at least 0.5 bar gauge. Switch off ignition, wait about 10 seconds and then switch it on again. The "coolant level" warning lamp must light up. Depressurize cooling system. Switch ignition off and on again. No warning lamp should light up.

8. Windshield/headlight washer water level

Remove cover plate from CEB in passenger foot well. Connect auxiliary cable to ground and other end to:

Connector K, terminal 5 (M14 model '85 and later) or

Connector Q, terminal 6 (none on '85).

(This circuit saves you from having to remove the guard plate in the right-hand wing — in front of the water reservoir.)

— Washer water WL, ZW and Q must light up after about 20 seconds. Press acknowledge button. ZW and Q go off, WL must continue glowing. The WL continues to glow after the connection is removed.

9. Fuel level

Remove cover plate from CEB in passenger footwell. Connect auxiliary cable to ground and other end to R15.

— Tank reserve WL, ZW and Q must light up after about 20 seconds. Press acknowledge button, ZW and Q go off, WL must continue glowing. Plug in connector, the WL continues to glow.

10. Brake circuit failure (up to Mod. 83) deleted from Model 84

Pull off one connector base from the brake light switch on the master cylinder and use auxiliary cable to join together the opposing connector sockets.

— Brake circuit WL, ZW and Q must flash. Press acknowledge button, all lamps must continue flashing. Disconnect connector bridge and reconnect connector base to brake light switch — all lamps, ZW, Q and WL, must continue flashing.

Note: The flashing warning indicator can only be cancelled by briefly disconnecting one battery cable.

— Repeat Section I or II for the following tests.

11. Brake fluid level

A pressure switch (extended float) can be seen at the top of the brake fluid reservoir Press this switch down — or bridge the cable connection.

— Brake fluid WL, ZW and Q must flash after about 20 seconds. Press acknowledge button, all lamps continue flashing. Release float pin, or disconnect bridge, all lamps (ZW, Q and WL) continue flashing.

12. Tail light /brake light

The tail and brake light is monitored by a lamp test unit behind the ZEL. The lamp test unit is new from Model 84 and can be retrofitted.

Switch on parking light, depress foot brake (brake light WL must go off). Check rear light function on vehicle. In order to check this item it is necessary to unscrew the rear light lens at one side of the vehicle. — Take out tail light bulb.

— Switch on parking light.

— Tail light WL, ZW and Q must light up after about 5 seconds Press acknowledge button -ZW and Q go off, WL must continue glowing.

The tail light WL goes off when the bulb is refitted. Switch off light! Remove brake light bulb -depress foot brake. Brake light WL, ZW and Q light up - press acknowledge button - ZW and Q go off, WL must continue glowing. The WL continues glowing when the bulb is refitted and only goes off after the brake has been depressed once.

Note: Ensure that both rear lights (brake/tail light) are fitted with bulbs of the same make and rating — the central warning will otherwise switch on the warning lamps although the lights are functioning properly.

12. ABS anti-skid (anti-lock) system

Remove relay XVII from CEB, switch on ignition.

— ABS WL, ZW and Q must light up. Press acknowledge button, ZW and Q must go off, WL must continue glowing. Refit relay.

13. Tooth belt tension

Disconnect plug connecter in front of belt housing.

- Tooth belt WL, ZW and Q must ligth up about 3 min. Press acknowledge button -ZW and Q go off. WL must continue glowing.

Note on operation — test points 7 and 7a - coolant level Coolant level up to Mod. 83

If we assume that the coolant level is so low on a cold engine that the transmitter contact is closed, the central warning will be connected to ground.

When the engine is started, a warning is given after about 20 seconds, i. e. generally during the journey. The coolant expands as it warms up, its volume increases and the coolant level rises. This results in the transmitter contact opening so that no warning is given when the engine is restarted (warm engine).

A visual inspection at the expansion tank may not, therefore, reveal that the coolant level is too low, i. e. when the engine is warm.

This can lead to a faulty diagnosis on the warning system because of it not being possible to reproduce a warning when the engine is warm.

Coolant level from Mod. 84

The central warning system has a pressure switch located in the return line to the expansion tank which now works in conjunction with the coolant level switch. If the coolant level of a cold engine is too low, this will switch on the coolant level warning light after a delay of approximately 20 seconds. Coolant will expand as the engine warms up and the coolant level will rise tf the engine is stopped and started again, the warning will go out. This happens, even though the cold coolant level is too low.

To avoid unnecessary troubleshooting, the pressure switch senses the pressure in the cooling system and sends this information to the central warning unit. Now if there had first been a warning from the coolant level switch and afterwards from the pressure switch, the central warning system will store this signal sequence and maintain the warning, even after the coolant has expanded and the coolant level switch has an opened circuit. In other words, when starting the engine again the warning lamp comes on, even if the coolant level appears correct, if the cap at the expansion tank is removed (io add coolant), pressure escapes and the pressure switch circuit opens. The central warning system, with this indication, assumes coolant has been added and turns the warning lamp out.

On the following pages you will find a chart showing the connections of the central indicator. The terminals that are actually connected are marked O —

What is the test procedure?

1. Bring warning system into testing position — Section I or II, page 33.

2. With the aid of the connection chart, use an auxiliary cable to apply the appropriate polarity from the rear, through the plugged in central warning control unit connector.

Caution: Terminals 12, 13, (14), 21 (black) are only used to check whether sutticient and correct voltage is applied - check only with voltmeter.

3. If the electrical warning circuit is in order, the warning lamps must light up at all test terminals on which all 3 warning lamps are shown.

e. y. terminal 15 yellow to ground = ZW, WL, Q must light up (warning system o k.)

terminal 2 yellow to ground = only WL should light up {connection from connector to WL o. k.)

Caution: Note delayed tripping of warning

4. The central warning is faulty if no warning ¡stripped at the terminals on which theZW, Q and WL are shown when you apply the appropriate polarity.

5. The feed line from the transmitter to the central warning is faulty if no warning Is tripped after the operational test, but there is a warning when the test as per "item 2" is carried out.

6. If the warning indicator lights when there is no fault, pull of the transmitter cable concerned. The warning Indicator must go off and must not come on again {except brake lining wear) — otherwise check wiring (may be connected to wrong ground or one of ground connections on vehicle is loose,), carry out separate test as per items 2 and 5.

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