VW Passat & Audi A4 1990-2000

Ignition Control Unit

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Testing

WARNING
Testing the ignition control unit requires the use of a high impedance digital volt/ohm meter (DVOM) and an LED test light such as Tool No. VAG 1527. A standard analog voltmeter or a standard incandescent 12-volt test light will cause damage to the unit.

The ignition control unit is tested using a logical step-by-step process by checking the input and output signals.

If the VAG 1551, VAG 1552 or equivalent diagnostic equipment is available, the first step in control unit testing is to check the control unit's fault memory. If this equipment is available, follow the manufacturer's instructions on its use and fault memory interrogation.


WARNING
When using diagnostic test equipment, always make sure the ignition is switched off before connecting the equipment to the electrical circuits.


NOTE
When performing the following tests, the vehicle's battery must be fully charged.


WARNING
Never crank the engine or turn the ignition switch on with a high-tension spark plug wire or ignition coil wire disconnected. If a plug wire or ignition coil wire is disconnected, it should be grounded before the ignition is switched on or the engine cranked.

Because control units rarely fail, make sure the failure is not do to one of the following, and repair/replace as necessary.



The control unit has not been exposed to excessive heat
 
The control unit has not been contaminated by fluids
 
The control unit has not been exposed to excessive moisture
 
The control unit has not been exposed to excessive vibration or impact
 
The related input and output components meet the manufacturer's specifications.
 
The vehicle's charging system is not overcharging. Symptoms include a dry battery and/or warped battery case
 



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Fig. The VAG LED test light, Tool No. TAG 152 7B0 28 ZEL, is a very useful tool for troubleshooting tests requiring the use of an LED test light



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Fig. An LED test light can be made using components from an electronics vendor

2.0L 9A Engine

If the VAG 1551, VAG 1552 or equivalent diagnostic equipment is available, the first step in control unit testing is to check the control unit's fault memory. If this equipment is available, follow the manufacturer's instructions on its use and fault memory interrogation.

Control Unit Output test
  1. Disconnect the electrical connector at the ignition coil.
  2.  
  3. Using an LED test light such as Tool No. VAG 1527 carefully connect the two leads to terminal positions 2 and 3 of the connector.
  4.  
  5. Turn the ignition key until the starter motor is engaged, and then hold the key in this position for 3 seconds. The LED test light should flash on and off while the starter is engaged and the engine turned over. If the light flashes the hall sensor and control unit are ok.
  6.  

If the light does not flash:



There may be a problem in the system wiring
 
The control unit may have failed
 
The hall sender may have failed
 

If all of the following hall sensor tests are found to be OK, and the ignition coil is OK, the control unit has likely failed. Generally, control units are reliable components. If the control unit is deemed defective and is to be replaced, make sure all of the related ignition system components meet the specifications of the manufacturer.

Next test the hall sender electrical circuit

Hall sensor electrical circuit test
  1. Turn the ignition switch to the OFF position.
  2.  
  3. Disconnect the 3-wire electrical connector at the distributor.
  4.  
  5. Using a suitable digital voltmeter, check for DC volts by carefully connecting the volt meter's electrical connectors to terminal positions 1 and 3 .
  6.  
  7. Turn the ignition switch to the ON position, but Do NOT engage the starter. The voltmeter should read at least 9 volts. If the voltage is less than 9 volts or non-existent check the wiring. If the reading is at least 9 volts, next test the hall sender unit output.
  8.  

hall sensor output test
  1. Make sure all wires and electrical connections are correctly and fully connected.
  2.  
  3. Carefully pull back the rubber protective cover for the 3-wire electrical connector at the distributor.
  4.  
  5. Carefully back-probe the center terminal of the electrical connector and connect an LED test light such as Tool No. VAG 1527, or its equivalent, to the probed center terminal and the positive ( + ) battery terminal.
  6.  
  7. Turn the ignition key and engage the starter. When the engine rotates the test light should flash. If the test light fails to flash, the hall sensor or its wiring is defective.
  8.  
  9. If the light flashes perform the ignition cold input test.
  10.  

Ignition coil input test
  1. Turn the ignition switch to the OFF position.
  2.  
  3. Connect a suitable digital voltmeter to the Nos. 1 ( - ) and 15 ( + ) terminals.
  4.  
  5. Disconnect the 3-wire electrical connector at the distributor.
  6.  
  7. Carefully connect a suitable jumper wire to the center terminal of the 3-wire connector of the wiring harness coming to the distributor.
  8.  
  9. Turn the ignition switch to the ON position, but Do NOT engage the starter.
  10.  
  11. With the ignition switch on, ground the jumper wire connected to the center terminal of the 3-wire connector for a short period of time. The voltage measured at the ignition coil should increase to a minimum of 2 volts and then fall to 0. If the voltage does not respond within the parameters of the test, either the ignition coil or the control unit has failed.
  12.  



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Fig. The numbering sequence of the 3-terminal female electrical connector as used on Audi and Volkswagen models

2.0L ABA Engine

If the VAG 1551, VAG 1552 or equivalent diagnostic equipment is available, the first step in control unit testing is to check the control unit's fault memory. If this equipment is available, follow the manufacturer's instructions on its use and fault memory interrogation.

A vital input component for the ignition control unit is the Crankshaft Position (CKP) Sensor also referred to as the crankshaft speed sensor and the Camshaft Position Sensor (CMP). Before proceeding with the following steps, check the operation of the CKP and CMP. For additional information, please refer to the following topic(s): Driveability and Emission Controls, Crankshaft Position Sensor, Crankshaft Speed Sensor, Camshaft Position Sensor

voltage supply check


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Fig. Checking for ignition control unit voltage at the harness connector

  1. Unplug the harness connector from the ignition control unit.
  2.  
  3. Using a digital voltmeter, connect the meter positive lead to terminal 4 and the negative lead to terminal 2 of the harness connector.
  4.  
  5. With the leads connected, turn the ignition switch ON and check for battery (12 volts) voltage.
  6.  
  7. If voltage does not exist, inspect the integrity of the wiring. For additional information, please refer to the following topic(s): Chassis Electrical, Wiring Diagrams
  8.  
  9. If 12 volts exists at the harness connector, proceed with the component check procedure.
  10.  

Component Check


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Fig. Connect the meter positive lead to terminal 4 and the negative lead to terminal 2 of the control unit harness connector



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Fig. Use a jumper wire to touch terminal 25 to ground

Before testing, visually inspect all components of the system. Replace any noticeably damaged parts. Be sure to check the ignition coil and replace if it is leaking fluid.

  1. Turn the ignition to the OFF position. Reconnect the control unit harness.
  2.  
  3. Unplug the harness connector from the control unit. Using a Digital Multimeter (DMM) switched to the 20V range, connect the meter positive lead to terminal 15 and the negative lead to terminal 1 of the ignition coil. If necessary, unplug the wiring from ignition coil terminal 1, then reconnect it so that only the wire to the Hall control unit is engaged.
  4.  
  5. Turn the ignition switch to the ON position. The meter must read 2 volts, minimum, then drop to 0 volts after 1-2 seconds. If not, replace the Hall control unit.
  6.  
  7. Using a jumper wire, briefly touch terminal 25 of the control unit harness connector to ground. Displayed voltage must rise briefly to 2 volts minimum.
  8.  
  9. Turn the ignition switch to the OFF position. Reconnect the control unit harness.
  10.  

REMOVAL & INSTALLATION
All 2.0L (9A And ABA) Engines

The ignition control unit is located in the cowling above the firewall in the engine compartment.

  1. Disconnect the negative battery cable.
  2.  
  3. Make sure the ignition key is in the OFF position.
  4.  
  5. Remove the rubber weather-strip seal from the firewall. Carefully pull the plastic drain tray from the cowling.
  6.  
  7. Unplug the connector from the ignition control unit.
  8.  
  9. Remove the screws securing the to the heat sink/bracket assembly.
  10.  
  11. Remove the ignition control unit control unit.
  12.  

To install:

  1. Clean the mating surface of the heat sink/bracket and the bottom of the ignition control unit. These surfaces must be free of any debris.
  2.  
  3. Spread an even coat of dielectric grease on the bottom of the ignition control unit (the bare metal side). The dielectric grease helps to make a better thermal connection between the ignition control unit and the heat sink.
  4.  
  5. Position the new ignition control unit on the heat sink/bracket, and then tighten the screws until snug.
  6.  
  7. Engage the electrical connection.
  8.  
  9. Install the idle stabilizer or plastic cowling cover and weather-strip seal as applicable.
  10.  
  11. Connect the battery cable.
  12.  

 
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