Engine Controls - Basic Testing Audi 90 B4

INTRODUCTION

The following diagnostic steps will help prevent overlooking a simple problem. This is also where to begin diagnosis for a no-start condition.

The first step in diagnosing any driveability problem is verifying the customer's complaint with a test drive under the conditions the problem reportedly occurred.

Before entering self-diagnostics, perform a careful and complete visual inspection. Most engine control problems result from mechanical breakdowns, poor electrical connections, or damaged/misrouted vacuum hoses. Before condemning the computerized system, perform each test listed in this article.

Note. Unless stated otherwise in test procedure, perform all voltage tests using a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance.

VISUAL INSPECTION

Visually inspect all electrical wiring, looking for chafed, stretched, cut or pinched wiring. Ensure electrical connectors fit tightly and are not corroded. Ensure vacuum hoses are properly routed and are not pinched or cut. See the appropriate VACUUM DIAGRAMS article in this section to verify routing and connections (if necessary). Inspect air induction system for possible vacuum leaks.

Compression

Check engine mechanical condition with a compression gauge, vacuum gauge, or an engine analyzer. See engine analyzer manual for specific instructions.

Exhaust System Backpressure

The exhaust system can be checked with a vacuum or pressure gauge. Remove O2 sensor or air injection check valve. Connect a 1-10 psi pressure gauge and operate engine at 2500 RPM. If exhaust system backpressure is greater than 2 psi, exhaust system or catalytic converter is plugged.

If a vacuum gauge is used, connect vacuum gauge hose to intake manifold vacuum port and start engine. Observe vacuum gauge. Open throttle part way and hold it steady. If vacuum gauge reading slowly drops after stabilizing, check exhaust system for restriction.

FUEL SYSTEM (2.2L)

Fuel Pressure Release (2.2L)

1. Remove fuel pump relay from fuse panel. Start engine. Let engine run until it stops. Turn ignition off. Disconnect negative battery terminal. Install fuel pump relay.
2. Use a rag to cover fuel system connection before disconnecting high pressure fuel system component for test or repair procedure. Some residual fuel pressure may still be in system.

System Pressure (2.2L)

1. Using adapter fittings, connect Pressure Gauge (VW 1318) between cold start valve fuel line and test port connection on lower chamber of fuel distributor. (Scheme 4) Test port is sealed by a threaded plug. Bridge fuel pump relay (located on fuse/relay panel) with Jumper Switch (US 4480/3). (Scheme 3)for fuel pump relay terminal location. NOTE: Fuel pump may also be activated by jumping 12 volts to by-pass terminal on fuse/relay panel. See appropriate WIRING DIAGRAMS article in this section.
2. Open valve on pressure gauge (points to cold start valve line when open) and activate fuel pump. System pressure must be 68-78 psi (4.7-5.4 kg/cm 2 ). If pressure reading is low and fuel pump delivery quantity is good, adjust or replace regulator assembly.
3. If pressure reading is high, disconnect fuel tank return line from fuel distributor. Repeat test. If reading is correct, check for plugged return line. If reading is incorrect with line open, replace regulator assembly.

Residual Pressure & Internal Leak Testing (2.2L)

1. Open valve on pressure gauge. Operate fuel pump for 30 seconds. Pressure can drop to a minimum of 38 psi (2.7 kg/cm 2 ) after 10 minutes. If pressure drops below specified value, inspect fuel pump check valve and all fuel fittings for leakage. NOTE: Pressure and leak testing DOES NOT include checking cold start valve.
2. If there are no leaks, check sensor plate clearance. If plate clearance is correct, replace regulator assembly and repeat step 1). If pressure drop is not as specified, replace fuel distributor "O" rings.

Main Pump Delivery Volume (2.2L)

1. Check transfer pump (if equipped) and fuel filter. Disconnect fuel return line and place open end in measuring container. Activate fuel pump with jumper switch. Check fuel pump delivery volume for 30-second period.
2. Minimum delivery volume is .71 qt. (.68L) in 30 seconds. With engine off and fuel pump activated with jumper switch, measure voltage at fuel pump. Voltage should be 11.4 volts.

Scheme 1

Scheme 2

1. Remove fuel pump relay from relay panel. Install Jumper Switch (US 4480/3). Attach Fuel Quantity Analyzer (US 4480) to bumper and secure in place. (Scheme 1) Remove injectors from cylinder head with fuel lines attached. Check and replace fuel injector "O" rings if necessary.
2. Check tightness of injector inserts (2-piece inserts). If inserts are loose, remove and clean threads. Use sealing compound when installing upper insert. Place sealing washer against cylinder head, below lower portion of insert. Lubricate injector "O" rings with gasoline. Install injectors with fuel lines connected into fuel quantity analyzer tubes.
3. Ensure lines are not kinked or bent. Loosen fittings to align fuel lines and retighten. Remove rubber boot from airflow sensor housing above sensor plate. Turn and lift setting screw and adjusting slide of Sensor Plate Adjustable Holder (VW 1348/1) into upper position. (Scheme 2) This simulates full throttle operation.
4. Place sensor plate adjustable holder on airflow sensor housing, with holder centered over plate. Pointer on edge of holder base must point toward center of fuel distributor. (Scheme 2) Push adjusting slide of holder down onto stop.
5. Turn adjusting screw clockwise until magnetic end touches sensor plate retaining bolt. Activate fuel pump with jumper switch. Turn adjusting screw of holder counterclockwise until an injector starts to deliver fuel. Turn off jumper switch and empty fuel quantity analyzer into fuel tank.
6. Idle injection quantity is measured first. Simulate sensor plate's idle by lifting adjusting slide of holder to first stop. Activate fuel pump with jumper switch until fuel level reaches 20 milliliters (ml) on scale of any tube for quantity comparison.
7. Ensure all injectors have identical spray patterns (even and cone-shaped). If spray patterns are not identical, raise sensor plate up quickly to full lift position and release. Repeat idle quantity test. Maximum difference in delivery quantity between injectors is 3.0 ml of fuel.
8. If fuel delivery quantity between high and low levels differs by more than 3.0 ml, interchange injectors and repeat test. If difference in delivery quantity between injectors changes, replace injectors. If difference in delivery quantity does not change, either fuel lines are pinched or fuel distributor is defective.
9. Measure full throttle injection quantity. Empty analyzer into fuel tank and reinstall injectors in analyzer. Lift adjusting slide of holder to last stop to simulate full throttle position of sensor plate.
10. Activate fuel pump with jumper switch until fuel level reaches 80 ml on scale of any analyzer tube. Ensure all injectors have identical spray patterns (even and cone-shaped). Maximum difference in delivery quantity between injectors is 8.0 ml of fuel.
11. If fuel delivery quantity between high and low levels differs by more than 8.0 ml, interchange injectors and repeat test. If difference in delivery quantity between injectors changes, replace injectors. If difference of delivery quantity does not change, either fuel lines are pinched or fuel distributor is defective.
12. Check fuel injectors for leakage immediately after delivery quantity test is complete. Set sensor plate in rest position. Activate fuel pump with jumper switch for 2 minutes. Injectors should not drip. Replace any dripping injectors.

Fuel Pump Relay (2.2L)

1. Remove fuel pump relay from relay board. Turn ignition on. Test light should light when connected between pump relay terminal No. 46 and ground. (Scheme 3)
2. While starter motor is operating, test light should flicker when connected to relay terminals No. 50 and No. 51. Test light should light when connected between relay terminals No. 46 and No. 50, and relay terminals No. 46 and No. 52.
3. If test light does not light for all tests, check wiring for short or open. If test light lights for all tests but there is no voltage at fuel pump with relay installed, replace fuel pump relay.

Scheme 3

Fuel Pressure Release (2.3L)

1. Remove fuel pump relay from fuse panel. Start engine. Let engine run until it stops. Turn ignition off. Disconnect negative battery terminal. Install fuel pump relay.
2. Use a rag to cover fuel system connection before disconnecting high pressure fuel system component for test or repair procedure. Some residual fuel pressure may still be in system.

System Pressure (2.3L)

1. Remove fuel line from cold start valve. Remove test plug from distributor lower chamber. Connect Pressure Gauge (VW 1318) between fuel line from cold start valve to lower chamber. (Scheme 4)
2. Disconnect differential pressure regulator connector from side of regulator. Remove fuel pump relay. Jump connector in fuel pump relay socket. Open valve on pressure gauge.
3. Energize fuel pump. Note pressure reading on pressure gauge. Pressure should be 88-94 psi (6.2-6.6 kg/cm 2 ). System pressure is not adjustable.

Residual Pressure (2.3L)

1. Connect Pressure Gauge (VW 1318) as previously described in SYSTEM PRESSURE test. (Scheme 4) Open pressure gauge valve. Operate fuel pump for at least 30 seconds.
2. Shut off fuel pump. Note system pressure. Pressure should be 51 psi (3.6 kg/cm 2 ) after 10 minutes and 49 psi (3.4 kg/cm 2 ) after 20 minutes.

Note. Residual pressure test DOES NOT include checking cold start valve. To check cold start valve, reattach fuel line. Operate fuel pump and visually check for leaks.

Fuel Pump Relay (2.3L)

1. With ignition off, remove fuel pump relay from relay panel. Connect multimeter between relay terminals No. 48 and No. 50. (Scheme 5) Multimeter should read battery voltage.
2. Connect multimeter between terminals No. 46 and No. 50. Turn ignition on. Multimeter should read battery voltage.
3. If multimeter does not read as specified, repair break in wiring. Connect multimeter between terminals No. 46 and No. 47. Momentarily engage starter. Multimeter should indicate 7 volts.
4. If multimeter does not indicate 7 volts, partially remove Ignition Control Unit (ICU) and disconnect harness connector. Turn ignition off. Using an ohmmeter, check continuity between ICU and fuel pump relay.
5. Connect ohmmeter between ICU connector terminal No. 3 and relay terminal No. 49, and between ICU connector terminal No. 14 and relay terminal No. 47. (Scheme 5)and (Scheme 16). Ohmmeter should indicate.2 ohm each time.
6. If reading is not.2 ohm, repair break in wiring. If reading is.2 ohm, replace knock sensor.

Scheme 4

FUEL PRESSURE RELEASE (2.8L V6)

Remove fuel pump relay. See COMPONENT LOCATIONS . Start engine. Allow engine to run until it stops. Turn ignition off. Disconnect negative battery cable. Slight pressure may remain in system. Before disconnecting any fuel system line, cover connector with a clean shop towel. Install fuel pump relay.

FUEL PRESSURE CHECKS (2.8L)

Note. If fuel comes out of fuel pressure regulator vacuum port when hose is disconnected, replace fuel pressure regulator.

System Pressure (2.8L)

1. Ensure fuse No. 13 (fuse No. 17 on Audi 100) is okay, fuel filter is in good condition and battery voltage is 12 volts minimum. See «COMPONENT LOCATIONS»(/audi/90/b4-1992-1995/remont/testing-diagnostics/#engine-controls-basic-testing) . Connect Pressure Gauge (VAG 1318) between fuel supply line and fuel rail. Open pressure gauge lever. Disconnect vacuum hose from fuel pressure regulator. Plug open end of vacuum hose.
2. Initiate OUTPUT DTM. See the «TESTS W/CODES»(/audi/90/b4-1992-1995/remont/testing-diagnostics/#engine-controls-self-diagnostics) article. Activate fuel pump relay. If fuel pump does not operate, check fuel pump. See FUEL DELIVERY. If fuel pump operates, check fuel pressure. If fuel pressure is 55-61 psi (3.8-4.2 bar), go to step 4).
3. If fuel pressure is not as specified, replace fuel pressure regulator and recheck pressure. If fuel pressure is less than specified, check for damaged fuel pump or restricted fuel supply line. If fuel pressure exceeds specification, check for restricted fuel return line. WARNING: Excessive fuel pressure may rupture fuel pressure regulator diaphragm, causing fuel to enter engine through vacuum hose. This could result in an explosion. NOTE: When vacuum hose is disconnected from fuel pressure regulator, mixture is enriched. DO NOT operate engine for longer than necessary with hose disconnected, as oxygen sensor limits may be exceeded, causing a code to set.
4. Turn off all electrical accessories. Run engine at idle (this automatically interrupts output DTM). Ensure radiator cooling fan is not running.
5. Difference in fuel pressure with vacuum hose connected and disconnected at fuel pressure regulator should be about 7.3 psi (0.5 bar). If difference is as specified, system is okay. If difference is not as specified, check for faulty vacuum hose or blocked vacuum port at intake manifold. Repair or replace as necessary. If hose and vacuum port are okay, replace fuel pressure regulator.

Residual Pressure (2.8L)

1. Connect Pressure Gauge (VAG 1318) between fuel supply line and fuel rail. Open pressure gauge lever. Start engine. Turn off engine. Wait 10 minutes. If fuel pressure is at least 31.9 psi (2.2 bar) with engine cold, or 43.5 psi (3.0 bar) with engine hot, system is okay.
2. If fuel pressure is as specified, check for leaks at pressure gauge connections and fuel lines. If no leaks are found, check fuel pump check valve. If check valve is okay, replace fuel pressure regulator.

FUEL DELIVERY (2.8L)

Note. Fuel pump connector is accessible through trunk floor.

Fuel Pump Circuit Without Scan Tester (90 - 2.8L)

1. Ensure fuse No. 13 is okay. See «COMPONENT LOCATIONS»(/audi/90/b4-1992-1995/remont/testing-diagnostics/#engine-controls-basic-testing). Ensure fuel filter is okay and battery is fully charged. While operating starter for several seconds, measure voltage at fuse No. 13.
2. If battery voltage is not present, go to next step. If battery voltage is present, check for open circuit between fuse No. 13 and fuel pump, and between fuel pump and ground. If circuit is okay, replace fuel pump.
3. Check fuel pump relay. See FUEL PUMP RELAY - NOT USING SCAN TESTER (90). If fuel pump relay is okay, remove it. Turn ignition on. Check voltage at fuel pump relay terminals No. 46 and 48. (Scheme 6) If battery voltage is not present, repair relay power supply circuit.
4. If battery voltage is present, check for open circuit between fuel pump relay connector terminal No. 52 and fuse No. 13. If circuit is okay, check for open circuit between fuel pump relay connector terminal No. 47 and ECM. If circuit is okay, replace ECM.

Fuel Pump Relay Without Scan Tester (90 - 2.8L)

Remove fuel pump relay. See COMPONENT LOCATIONS. Without voltage applied to relay, there should be no continuity between terminals No. 48 and 52, and between terminals No. 48 and 59. (Scheme 6) With battery voltage applied across terminals No. 28 and 29, there should be continuity between terminals No. 48 and 52, and between terminals No. 48 and 59. If continuity is not as specified, replace relay.

Fuel Pump Relay Using Scan Tester (90 - 2.8L)

1. Remove fuse No. 13. See «COMPONENT LOCATIONS»(/audi/90/b4-1992-1995/remont/testing-diagnostics/#engine-controls-basic-testing). Using jumper wire from Adaptor Kit (VW 1594), connect LED Tester (VAG 1527B) between chassis ground and rear terminal of fuse No. 13 receptacle.
2. Initiate OUTPUT DTM. In output DTM, activate fuel pump relay. Fuel pump relay should click and LED should come on. If fuel pump relay does not click, go to step 6). If fuel pump relay clicks but LED does not come on, remove fuel pump relay. Check for faulty wiring between fuse No. 13 and terminal No. 52 of fuel pump relay connector. (Scheme 6)
3. If wiring is okay, install fuel pump relay and fuse No. 13. Remove fuse No. 28. Connect LED tester between chassis ground and either terminal of fuse No. 28 receptacle.
4. In output DTM, activate fuel pump relay. Fuel pump relay should click and LED should come on. If fuel pump relay does not click, go to step 6). If fuel pump relay clicks but LED does not come on, connect LED tester between chassis ground and other terminal of fuse No. 28 receptacle.
5. In output DTM, activate fuel pump relay. If LED still does not come on, remove fuel pump relay. Check wiring between fuse No. 28 and terminal No. 59 of fuel pump relay connector. If wiring is faulty, repair or replace wiring as necessary. If wiring is okay, replace fuel pump relay.
6. Turn ignition off. Remove fuel pump relay. Turn ignition on. Check voltage between relay connector terminals No. 46 and 50, and terminals No. 48 and 50. (Scheme 6)
7. If battery voltage is not present across both sets of terminals, repair wiring. If battery voltage is present across both sets of terminals, connect LED tester between terminals No. 46 and 47. When ignition is turned on, LED should come on brightly for about 1 second, then become dim and stay dim. When starter is engaged, LED should become distinctly brighter.
8. If LED comes on, replace fuel pump relay. If LED does not come on, use Adaptor Cable (1598/12) to connect Test Box (VAG 1598) to Engine Control Unit (ECU) wiring harness connector. Leave ECU disconnected.
9. Measure resistance between relay connector terminal No. 47 and test box terminal No. 15. If resistance is more than one ohm, repair wiring as necessary. If resistance is less than one ohm, replace ECU.

Scheme 5

Fuel Pump Circuit (100 - 2.8L)

1. Ensure fuse No. 17 is okay. See «COMPONENT LOCATIONS»(/audi/90/b4-1992-1995/remont/testing-diagnostics/#engine-controls-basic-testing). Ensure fuel filter is okay and battery is fully charged. While operating starter for several seconds, measure voltage at fuse No. 17.
2. If battery voltage is not present, go to next step. If battery voltage is present, check for open circuit between fuse No. 17 and fuel pump, and between fuel pump and ground. If circuit is okay, replace fuel pump. NOTE: Fuel pump connector is accessible through cover on trunk floor.
3. Check fuel pump relay. See FUEL PUMP RELAY (100). If relay is okay, remove fuel pump relay. Turn ignition on. Check voltage at fuel pump relay terminals No. 28 and 30. (Scheme 7) If battery voltage is not present, repair relay power supply circuit.
4. If battery voltage is present, check for open circuit between fuel pump relay connector terminal No. 30 and fuse No. 17. If circuit is okay, check for open circuit between fuel pump relay connector terminal No. 29 and ECM. If circuit is okay, replace ECM.

Fuel Pump Relay (100 - 2.8L)

Remove fuel pump relay. See COMPONENT LOCATIONS. Without voltage applied to relay, there should be no continuity between terminals No. 30 and 32, and between terminals No. 31 and No. 32. (Scheme 7) With battery voltage applied across terminals No. 28 and 29, there should be continuity between terminals No. 30 and 32, and between terminals No. 31 and 32. If continuity is not as specified, replace relay.

Scheme 6

Fuel Injectors (2.8L)

1. Disconnect fuel injector connector. Measure resistance across fuel injector connector terminals. If resistance is not 15-17 ohms, replace fuel injector. If resistance is 15-17 ohms, connect LED Tester (US 1115) between engine ground and fuel injector connector terminal No. 2. (Scheme 8)
2. Operate starter for several seconds. If LED comes on, go to next step. If LED does not come on, check fuel pump relay, circuit breaker and wiring. See FUEL DELIVERY. If fuel pump relay, circuit breaker and wiring are okay, connect LED tester between battery positive source and fuel injector connector terminal No. 1.
3. Operate starter for several seconds (engine may start). If LED flashes, fuel injector system is okay. If LED does not flash, check for faulty wiring. If wiring is okay, replace ECU. See «COMPONENT LOCATIONS»(/audi/90/b4-1992-1995/remont/testing-diagnostics/#engine-controls-basic-testing).

Fuel Injector Leakage & Volume (2.8L)

1. Ensure fuel system pressure is okay. Refer to the appropriate TESTS W/O CODES article. Remove intake air hose between airflow sensor and noise damper. Disconnect and move spark plug wires out of way to allow fuel rail to be removed.
2. Disconnect fuel injector connectors. Disconnect vacuum hose from fuel pressure regulator. Remove fuel rail from manifold with injectors attached to fuel rail. Suspend fuel rail with wire. In Output DTM, activate fuel pump relay. See OUTPUT DTM in the appropriate «TESTS W/CODES»(/audi/90/b4-1992-1995/remont/testing-diagnostics/#engine-controls-self-diagnostics) article. If more than 2 drops of fuel per minute falls from fuel injector, replace fuel injector and "O" ring.
3. If less than 2 drops of fuel per minute falls from fuel injector, set a clear measuring container under fuel injector to be tested. Connect jumper wire between engine ground and one terminal of fuel injector. For 30 seconds, connect jumper wire between battery positive source and other terminal of fuel injector connector.
4. If output is 85-100 milliliters, volume is okay. If output is not 85-100 milliliters, replace fuel injector.

Oxygen (O2) Sensor Heating Element (2.8L)

1. Disconnect O2 sensor heating element connector. See «COMPONENT LOCATIONS»(/audi/90/b4-1992-1995/remont/testing-diagnostics/#engine-controls-basic-testing) . Connect voltmeter between harness connector terminals. Start engine and let idle. If battery voltage is not present, check for faulty circuit breaker, wiring or fuel pump relay.
2. If battery voltage is present, connect Test Cable (VAG 1315 A/1) to oxygen sensor heating element connector. Run engine at idle. Set ammeter on 10-amp scale. Check amperage at test cable terminals. If 0.5-3.0 amps is present, heating element is okay. If 0.5-3.0 amps is not present, replace oxygen sensor.

Scheme 7

Note. To check oxygen sensor control function, read individual measuring values in channels 2 and 3. See READING INDIVIDUAL MEASURING VALUES in the TESTS W/CODES article.

Oxygen (O2) Sensor Control (2.8L)

1. Disconnect oxygen sensor connector. See «COMPONENT LOCATIONS»(/audi/90/b4-1992-1995/remont/testing-diagnostics/#engine-controls-basic-testing) . Measure resistance between engine ground and oxygen sensor connector terminal (component side of connector). If resistance is not infinite, replace oxygen sensor.
2. If resistance is infinite, set voltmeter on 2 volt DC scale. Turn ignition on. Measure voltage between engine ground and oxygen sensor connector terminal (component side of connector). If 350-450 millivolts are present, oxygen sensor is okay. If 350-450 millivolts are not present, check wiring. If wiring is okay, replace ECU.

Electronic Control Unit (ECU) Voltage Supply

1. Unplug ECU harness connector. Connect voltmeter positive test lead to pin No. 35. (Scheme 9) Turn ignition switch on, and touch negative test lead to either terminal No. 18 or No. 9. Voltmeter should indicate battery voltage. If battery voltage is not present, repair ignition circuit 15 or battery to ignition switch.
2. Turn ignition switch off. Connect positive voltmeter lead to terminal No. 32 and negative lead to No. 9. With ignition switch on, ensure battery voltage is present when brake pedal is depressed. If battery voltage is not present, check wiring for open or check brakelight switch. Turn ignition switch off. Reconnect ECU harness connector.

Engine Speed Sensors

1. Remove Gray (engine RPM) and Black (ignition timing reference) connectors from bracket near ignition coil. For each connector, check continuity between terminals No. 1 and No. 2. (Scheme 10) Ohmmeter reading should be 1000 ohms.
2. If reading is not 1000 ohms, replace sensor(s). If reading is 1000 ohms, check continuity between terminals No. 1 and No. 3, and terminals No. 2 and No. 3 of each connector. If ohmmeter indicates infinity, go to next step. If ohmmeter does not indicate infinity, replace sensor(s).
3. Unplug connector from ECU. Check wiring, on harness side of connectors, between each sensor and ECU. See ENGINE SPEED SENSOR CIRCUITS table. (Scheme 6)and (Scheme 7). Ensure resistance of each wire between ECU and sensor connectors is zero ohm.
4. Ensure clearance between ignition timing reference sensor and flywheel pin is.43" (1.10 mm). If engine speed sensors and wiring circuits are okay, replace ECU.

ENGINE SPEED SENSOR CIRCUITS

Scheme 8

Scheme 9

Note. Terminal identifications for Hall Effect sending unit are located on connector.

Hall Effect Sending Unit

1. Remove protective cover from Hall Effect sending unit (on distributor) and unplug 3-wire connector from unit. Connect voltmeter to connector terminals No. 1 and No. 3. Turn ignition on. Voltmeter reading should be 9 volts minimum.
2. If reading is not as specified, check for open circuit in wiring between sending unit and ECU terminals No. 23 and No. 25. (Scheme 9)for ECU terminal identifications. If reading is as specified, turn ignition off. Move back connector cover to gain access to rear of 3-wire connector. Reinstall 3-wire connector to distributor Hall sending unit.
3. Connect voltmeter between terminals No. 1 and No. 2 at rear of 3-wire connector. Remove distributor cap, rotor and dust cover. Turn crankshaft by hand until rotor window clears sending unit. Turn ignition on. Voltmeter should read minimum of 4 volts.
4. Turn crankshaft until rotor window aligns with sending unit. Voltmeter should read 0-.5 volt. Turn ignition off. If readings are not as specified, replace Hall Effect sending unit. If readings are as specified, check wiring between Hall Effect sending unit and ECU for open or short circuit and repair as necessary. If circuits are okay, replace ECU.

Knock Sensor

Knock sensor will produce a small voltage of about 50-70 millivolts if engine knocking is present. Check fuel quality, compression pressure, knock sensor and wiring circuits if knocking exists. No other tests are available from the manufacturer.

Spark Plug Wires & Rotor

1. Check coil wire resistance. Coil wire resistance reading should be 1200-2800 ohms if radio suppression wires are used, otherwise resistance should be zero ohm.
2. Check resistance of spark plug wires. Resistance should be 4600-7400 ohms if radio suppression wires are used, otherwise resistance should be 600-1400 ohms.
3. Check resistance of spark plug connectors. Resistance should be 4000-6000 ohms if radio suppression connectors are used, and 600-1400 ohms if radio suppression connectors are not used.
4. Check rotor and spark plug wire distributor cap connectors. Resistance of each connector should be 600-1400 ohms. Ensure rotor is marked R1.

Ignition Coil Resistance Check

1. Using ohmmeter, check ignition coil primary and secondary resistance. Disconnect coil primary and secondary ignition leads. Connect ohmmeter leads across primary terminals No. 1 and No. 15 at coil. (Scheme 11) Resistance value should be.5-1.5 ohms.
2. Connect ohmmeter leads between positive terminal No. 1 and coil high voltage tower. (Scheme 12) Secondary resistance value should be 5000-9000 ohms. If resistance values are not as specified, replace ignition coil.

Scheme 10

Scheme 11

1. Check Blue wire from terminal No. 1 of ignition coil to power transistor for damage. Repair if necessary. Remove secondary ignition wire from coil tower. Using a jumper wire, connect coil tower wire to ground.
2. Disconnect power transistor connector (next to ignition coil). Connect voltmeter between Green/White wire terminal and ground. (Scheme 11) Connect a jumper wire between Brown/White wire terminal and ground. NOTE: Ensure test lead connections are correct. If leads are reversed, ECU will be damaged.
3. Crank engine. Ensure voltmeter reading is.20 volt minimum. If reading is not as specified, check wiring between switching module and control unit connector as follows. NOTE: Power transistor terminal identifications are located on connector.
4. Unplug ECU connector. Using an ohmmeter, check continuity between terminal No. 2 of ECU connector and terminal No. 2 of power transistor connector. (Scheme 9)for ECU terminal identifications.
5. Also check continuity between ECU connector terminal No. 22 and power transistor connector terminal No. 1. Ohmmeter reading should be close to zero ohm for both tests. If readings are not as specified, check for open circuit between ignition control unit and switching module. If wiring is okay, replace ECU.

Tachometer Signal Output

1. Peel back ECU connector boot. Attach voltmeter positive lead to ECU terminal No. 7. Connect negative lead to a good ground. Start engine and check for steady voltage increase as RPM is increased.
2. If engine does not run, check engine speed sensors. If engine runs but voltage does not increase, replace ECU. If voltage increases but vehicle tachometer does not respond, check wiring between ECU terminal No. 7 and tachometer. If wiring is okay, repair or replace tachometer.

2.3L

Note. On vehicles with 2.3L engine, 2 versions of ignition coils are used. Both versions use a power stage. DO NOT test power stage function separately. (Scheme 11)-15 to identify version.

Ignition Coil & Power Stage

1. On version 1, disconnect ignition coil power stage connector. (Scheme 13) On version 2, disconnect ignition coil power stage connector; remove coil wire from ignition coil and remove screw from top of assembly. (Scheme 15)
2. On both versions, connect Multimeter (US 1119) between ignition coil power stage connector pin No. 1 and ground. Connect multimeter between pins No. 1 and No. 3. (Scheme 14) Turn ignition on. If battery voltage is not present, repair break in wiring.
3. If battery voltage is present, connect multimeter between pins No. 2 and No. 3. Crank engine with starter. If battery voltage exists, check ignition coil. If battery voltage does not exist, check wiring between pin No. 2 of connector and terminal No. 16 of ICU connector. If wiring is okay, replace ICU.

Scheme 12

Scheme 13

Scheme 14

Primary Resistance

1. On version 1, disconnect ignition coil power stage connector and ignition coil wire. (Scheme 13) On version 2, disconnect ignition coil power stage connector and remove screw from top of assembly. (Scheme 15)
2. On both versions, connect Multimeter (US 1119) between ignition coil positive (+) and negative () terminals. (Scheme 13)and (Scheme 14). Reading should be.5-1.5 ohms. If reading is not as specified, replace ignition coil.
3. If primary resistance is within specification but there is no ignition, replace ignition coil and power stage as an assembly.

Secondary Resistance

1. Check power stage ground wire, and wiring between power stage and ignition coil for corrosion or damage. On version 1, disconnect ignition coil power stage connector and ignition coil wire. (Scheme 13)
2. On version 2, disconnect ignition coil power stage connector and remove screw from top of assembly. (Scheme 15) On both versions, connect Multimeter (US 1119) between ignition coil positive (+) terminal and coil wire socket. (Scheme 16)and (Scheme 17).
3. Resistance should be 5000-9000 ohms. If resistance is not as specified, replace ignition coil.

Scheme 15

Scheme 16

Hall Sender

1. Disconnect coil wire from distributor cap. Use a jumper wire to ground coil wire. Disconnect Hall sender-to-ICU harness connector.
2. Connect multimeter between terminals No. 1 and No. 3 of connector "D". (Scheme 18) Turn ignition on. Reading should be at least 9 volts. If reading is not as specified, check for open circuit and repair if necessary. If circuit is okay, turn ignition off and go to next step.
3. Push back rubber boot on Hall sender connector. Connect multimeter between terminals No. 1 and No. 2. Connect Hall sender-to-ICU harness connector. Turn ignition on. Remove ignition distributor cap, rotor and dust cap. CAUTION: DO NOT allow spring clips to fall inward toward trigger wheel.
4. Using Wrench (2079), turn crankshaft. Multimeter should read a minimum of 4 volts when trigger wheel is clear of Hall sender, and 0-.5 volt when trigger window aligns with Hall sender. Turn ignition off.
5. If readings are not as specified, replace Hall sender. If readings are as specified, check wiring between Hall sender connector and ICU. Remove ICU cover from left side kick panel. Disconnect harness connector from ICU.
6. Disconnect connector "D" from distributor. Check continuity between distributor connector terminals and appropriate 25-pin ICU connector terminals. See appropriate WIRING DIAGRAMS article in this section. If Hall sender and wiring between connector "D" and ICU connector tested okay, replace ICU.

Scheme 17

Scheme 18

Power Output Stage (2.8L V6)

1. Disconnect power output stage 4-pin connector. See «COMPONENT LOCATIONS»(/audi/90/b4-1992-1995/remont/testing-diagnostics/#engine-controls-basic-testing) . Connect LED Tester (1527B) between vehicle battery positive source and Brown/Red wire (ground) terminal of power output stage 4-pin connector. If LED does not come on, repair Brown/Red wire.
2. If LED comes on, disconnect all fuel injector electrical connectors. Turn ignition on. Connect LED tester between engine ground and remaining 3 terminals of power output stage 4-pin connector, in sequence. Operate starter for several seconds while probing each terminal.
3. If LED comes on, replace ignition coil power output stage. If LED does not come on, check wiring between ECU and power output stage. If wiring is okay, replace ECU.

Ignition Coil Primary Resistance (2.8L V6)

Disconnect ignition coil 3-pin connector. See COMPONENT LOCATIONS. Disconnect power output stage 3-pin connector. Measure resistance between matching terminals of each connector (terminals No. 1 and 1, 2 and 2, and 3 and 3). (Scheme 20) If resistance is not 0.5-1.0 ohm, replace appropriate coil.

Scheme 19

Ignition Coil Primary Voltage Supply (2.8L V6)

Turn ignition on. Disconnect ignition coil 3-pin connector. See COMPONENT LOCATIONS . Connect LED Tester (VAG 1527B) between engine ground and each terminal of ignition coil 3-pin connector, in sequence. If LED comes on when terminals are probed, voltage supply is okay. If LED does not come on, check fuse No. 32 and wiring. Repair or replace as necessary.

Ignition Coil Secondary Resistance (2.8L V6)

Disconnect spark plug wires from ignition coil being tested. Measure resistance between coil towers of ignition coil being tested. If resistance is 9000-14,000 ohms, coil secondary circuit is okay. If resistance is not 9000-14,000 ohms, replace coil.

IDLE SPEED, CO LEVEL & IGNITION TIMING

Ensure idle speed and ignition timing are within specification. See the IDLE SPEED & CO LEVEL SPECIFICATIONS and IGNITION TIMING tables. For adjustment procedures, see the appropriate ADJUSTMENTS article in this section.

IDLE SPEED & CO LEVEL SPECIFICATIONS

IGNITION TIMING

Scheme 20

Scheme 21

Scheme 22

Scheme 23

SUMMARY

If no faults were found while performing basic test procedures in the BASIC TESTING , proceed to the appropriate G - TESTS W/ CODES article in this section. If no hard codes are found in G - TESTS W/ CODES, go to the TESTS W/O CODES article in this section for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.

See also:
• TESTS W/CODES
• COMPONENT LOCATIONS