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Engine Controls - System/component Tests Audi 90 B4

Testing & Diagnostics 8 illustrations ~4797 words

INTRODUCTION

Before testing separate components or systems, perform preliminary inspection. Since many computer-controlled and monitored components set a trouble code if they malfunction, also perform procedures in the TESTS W/CODES article.

Note. Testing individual components does not isolate shorts or opens. Perform all voltage tests using a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance unless otherwise instructed in test procedure. Use ohmmeter to isolate wiring harness shorts or opens.

ELECTRICAL COMPONENT LOCATIONS

ComponentLocation
Circuit Breakers(1) In Passenger Footwell, In Electronic Box
Closed Throttle Position (CTP) SwitchPart Of TP Sensor
Component Connectors(Scheme 25)
Crankshaft Position (CKP) SensorOn Left Side Of Cylinder Block
Data Link Connector (DLC)Behind Left Side Of Dash
Electronic BoxIn Passenger Footwell, Under Glove Box
Elect. Control Unit (ECU)Passenger Footwell, In Electronic Box
EGR Control Solenoid ValveIn Right Rear Corner Of Engine Bay
EGR Temperature SensorLeft Rear Corner Of Engine, On EGR Valve
Engine Coolant Temperature (ECT) SensorTo Rear Of Left Cylinder Head, On Coolant Pipe
Engine Speed SensorOn Left Side Of Transmission Bellhousing
EVAP Control Solenoid ValveIn Right Rear Corner Of Engine Bay
Fuel Pump RelayUnder Left Side Of Instrument Panel, In Fuse/Relay Block
FusesIn Fuse/Relay Block
Fuse/Relay BlockBehind Left Side Of Instrument Panel
Hall Sensor (Camshaft Position Sensor)On Rear End Of Left Cylinder Head
Idle Air Control (IAC) ValveRight Rear Corner Of Intake Manifold
Intake Manifold Change-Over (IMCO) Valve Control SolenoidIn Right Rear Corner Of Engine Bay
Kickdown SwitchOn Throttle Body
Knock Sensor No. 1On Right Cylinder Bank, Under Intake Manifold
Knock Sensor No. 2On Left Cylinder Bank, Under Intake Manifold
Mass Airflow SensorIn Air Intake Hose
Power Output StageOn Right Side Of Engine Bay Firewall
Throttle Position (TP) SensorOn Throttle Body
(1) Circuit breakers are identified by color: fuel injectors (Red), ignition coil (Yellow), mass airflow sensor (Black) and oxygen sensor (Brown).
(1)Circuit breakers are identified by color: fuel injectors (Red), ignition coil (Yellow), mass airflow sensor (Black) and oxygen sensor (Brown).

ELECTRICAL COMPONENT LOCATIONS

Scheme 25

Scheme 25
Scheme 25

Intake Manifold Change-Over (IMCO) Valve

  1. Increase engine speed to more than 4100 RPM. If IMCO valve vacuum motor is actuated, system is okay. If IMCO valve vacuum motor is not actuated, disconnect electrical connector from IMCO valve control solenoid. See «ELECTRICAL COMPONENT LOCATIONS»(/audi/90/b4-1992-1995/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) table.
  2. Measure resistance across terminals of IMCO valve control solenoid. If resistance is not 25-35 ohms, replace IMCO valve control solenoid. If resistance is 25-35 ohms, apply battery voltage across terminals of IMCO valve control solenoid. Replace IMCO valve control solenoid if it does not operate. If IMCO valve control solenoid operates, check ECU and wiring.

A/C COMPRESSOR ON SIGNAL (WITH ECU PART NO. 8A0 906 266A)

  1. Enter ENGINE BASIC SETTING mode. See the appropriate «TESTS W/CODES»(/audi/90/b4-1992-1995/remont/testing-diagnostics/#engine-controls-self-diagnostics) article. Observe channel 7. On vehicles with automatic A/C, press AUTO button, HI temperature button and HI blower button. On vehicles with manual A/C, press A/C button.
  2. On all vehicles, if value displayed on channel 7 increases by at least 64 when A/C is turned on, A/C compressor ON signal is okay. If displayed value does not change as specified, turn ignition off. Connect Test Box (VAG 1598) to ECU using Harness Adaptor (1598/11). See «ELECTRICAL COMPONENT LOCATIONS»(/audi/90/b4-1992-1995/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) table.
  3. Connect LED Tester (VAG 1527B) between test box terminals No. 11 and 45. Turn ignition on. Turn A/C on as in step 1). If LED comes on, replace ECU. If LED does not come on, check circuit between A/C-heater control panel and ECU. If circuit is okay, replace A/C-heater control panel.

A/C COMPRESSOR ON SIGNAL (WITH ECU PART NO. 8A0 906 266B)

  1. Enter READ MEASUREMENT BLOCK mode (display group 4). See the «TESTS W/CODES»(/audi/90/b4-1992-1995/remont/testing-diagnostics/#engine-controls-self-diagnostics) article. In display field 4, observe first digit of 4-digit display value (switch inputs).
  2. Value should be zero. Disregard remaining digits. On vehicles with automatic A/C, press AUTO button, LO temperature button and HI blower button. On vehicles with manual A/C, press A/C button.
  3. On all vehicles, if "1" is not displayed as first digit of 4-digit display, go to next step. If "1" is displayed, press right arrow button. Input 06 for END DATA TRANSMISSION and acknowledge with "Q" button. Turn ignition off. Connect Test Box (VAG 1598) to ECU using Harness Adaptor (1598/11). See «ELECTRICAL COMPONENT LOCATIONS»(/audi/90/b4-1992-1995/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) table.
  4. Connect LED Tester (VAG 1527B) between test box terminals No. 11 and 45. Turn ignition on. Turn A/C on as in step 2). If LED comes on, replace ECU. If LED does not come on, check circuit between A/C-heater control panel and ECU. If circuit is okay, replace A/C-heater control panel.

A/C COMPRESSOR CUT-OUT SIGNAL (W/ECU PART NO. 8A0 906 266A)

  1. Ensure A/C operates, no DTC codes are stored in ECU memory and vehicle temperature is 59°F (15°C) or greater. Start engine. On vehicles with automatic A/C, press AUTO button, LO temperature button and HI blower button. On vehicles with manual A/C, press A/C button.
  2. On all vehicles, compressor symbol must come on and A/C compressor must run. Enter ENGINE BASIC SETTING mode (display group 00). See the «TESTS W/CODES»(/audi/90/b4-1992-1995/remont/testing-diagnostics/#engine-controls-self-diagnostics) article. If A/C compressor stops, cut-out signal is okay.
  3. If A/C compressor does not stop, turn A/C off. Leave engine idling. Enter READ MEASUREMENT BLOCK mode. Turn A/C on as instep 1). If 116 is displayed in sector 7, go to step 5). If 116 is not displayed in sector 7, check for the following conditions and correct as necessary: Closed throttle position switch is not closed (linkage may be preventing throttle from returning to idle) Incorrect switch setting at A/C-heater control panel Transmission is in gear (A/T).
  4. If none of the above conditions exist, check circuit between ECU and A/C clutch control module (manual A/C) or between ECU and A/C-heater control panel (automatic A/C). Refer to the «ELECTRICAL COMPONENT LOCATIONS»(/audi/90/b4-1992-1995/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) table. Repair circuit if faulty. If circuit is okay, repair A/C electrical system.
  5. Quickly snap throttle open fully. Displayed value should briefly drop to 68 and rise to 84 after accelerator pedal is released, and 116 should be displayed again several seconds later. If displayed value is not as specified, replace ECU.
  6. If displayed value is as specified and A/C compressor shuts off when snapping throttle open, cut-out signal is okay. If displayed value is as specified but A/C compressor does not shut off when snapping throttle open, repair A/C electrical system.

A/C COMPRESSOR CUT-OUT SIGNAL (W/ECU PART NO. 8A0 906 266B)

  1. Ensure A/C operates, no DTC codes are stored in ECU memory and vehicle temperature is 59°F (15°C) or greater. Start engine. On vehicles with automatic A/C, press AUTO button, LO temperature button and HI blower button. On vehicles with manual A/C, press A/C button.
  2. On all vehicles, compressor symbol must come on and A/C compressor must run. Enter ENGINE BASIC SETTING mode (display group 00). See the «TESTS W/CODES»(/audi/90/b4-1992-1995/remont/testing-diagnostics/#engine-controls-self-diagnostics) article. If A/C compressor stops, go to step 6).
  3. If A/C compressor does not stop, turn A/C off. Leave engine idling. Enter READ MEASUREMENT BLOCK mode (display group 04). In display field 4, observe second digit of 4-digit display value (switch inputs). Disregard all other digits. With A/C off, zero should be displayed. With A/C turned on as in step 1), "1" should be displayed.
  4. If displayed values are as specified, go to step 6). If displayed values are not as specified, ensure A/C-heater control panel settings are as specified.
  5. If settings are as specified, check circuit between ECU and A/C clutch control module (manual A/C) or between ECU and A/C-heater control panel (automatic A/C). Refer to the «ELECTRICAL COMPONENT LOCATIONS»(/audi/90/b4-1992-1995/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) table. Repair circuit if faulty. If circuit is okay, repair A/C electrical system.
  6. Quickly snap throttle open fully. Displayed value should briefly drop to zero and rise to "1" after accelerator pedal is released. If displayed value is not as specified, replace ECU. If displayed value is as specified, but A/C compressor did not shut off, repair A/C electrical system.

Note. Closed throttle position switch (idle switch) is part of throttle position sensor.

CLOSED THROTTLE POSITION (CTP) SWITCH

  1. Ensure throttle cable is adjusted. See THROTTLE CABLE in ON-VEHICLE ADJUSTMENTS article. Remove noise damper. Disconnect TP sensor connector. Measure resistance between terminals No. 4 and 6 of TP sensor connector. (Scheme 28)
  2. Resistance should be zero ohms. Open throttle slightly. Resistance should be infinite (open). If resistance is not as specified, adjust closed throttle position (CTP) switch. See CLOSED THROTTLE POSITION (CTP) SWITCH in the ADJUSTMENTS article. Replace TP sensor if resistance cannot be obtained after adjustment.
  3. After adjustment, perform BASIC ENGINE SETTING. Refer to the «TESTS W/CODES»(/audi/90/b4-1992-1995/remont/testing-diagnostics/#engine-controls-self-diagnostics) article. Observe displayed value in channel 2.

CRANKSHAFT POSITION (CKP) SENSOR

Disconnect CKP sensor connector. Refer to the ELECTRICAL COMPONENT LOCATIONS table. Measure resistance between specified terminals of CKP sensor connector. See CKP SENSOR RESISTANCE table. (Scheme 26) If resistance is not as specified, replace CKP sensor. If resistance is as specified, check wiring between CKP sensor and ECU. If wiring is okay, replace ECU.

TerminalsOhms
1 & 21000
1 & 30
2 & 30

CKP SENSOR RESISTANCE

Scheme 26

Scheme 26
Scheme 26

ENGINE COOLANT TEMPERATURE (ECT) SENSOR

Disconnect ECT sensor connector. Refer to the ELECTRICAL COMPONENT LOCATIONS table. Measure resistance between ECT sensor terminals. If resistance is not as specified, replace ECT sensor. See the ECT SENSOR RESISTANCE table. If resistance is as specified, check wiring. If wiring is okay, replace ECU.

TemperatureOhms
68°F (20°C)Approximately 2500
176°F (80°C)Approximately 330

ECT SENSOR RESISTANCE

ENGINE SPEED SENSOR

  1. Raise left front wheel off of ground. Read individual measuring values in channels 15. See READ INDIVIDUAL MEASURING VALUES MODE in the «TESTS W/CODES»(/audi/90/b4-1992-1995/remont/testing-diagnostics/#engine-controls-self-diagnostics) article. With ignition on, turn left front wheel by hand and observe engine RPM displayed on Scan tester (VAG 1551).
  2. If RPMs are displayed, engine speed sensor is okay. If RPMs are not displayed, check for faulty wiring. If wiring is okay, replace ECU. See «ELECTRICAL COMPONENT LOCATIONS»(/audi/90/b4-1992-1995/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) table.

HALL SENSOR (CAMSHAFT POSITION SENSOR)

  1. Disconnect hall sensor connector. Refer to the «ELECTRICAL COMPONENT LOCATIONS»(/audi/90/b4-1992-1995/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) table. Connect Test Box (VAG 1598) to ECU with Adaptor Cable (VAG 1598/11). Connect LED Tester (1115) between test box terminals No. 8 and 46. Operate starter for several seconds.
  2. If LED flashes at each second engine revolution, go to next step. If LED does not flash at each second engine revolution, check for faulty wiring. If wiring is okay, go to next step.
  3. Turn ignition on. Check voltage between test box terminals No. 7 and 45. If 9 volts minimum is not present, replace ECU. If 9 volts minimum is present, check voltage between test box terminals No. 8 and 45. If 4 volts minimum is not present, replace ECU. If 4 volts minimum is present, replace hall sender.

KICKDOWN SWITCH

Remove noise damper. Disconnect kickdown switch connector. See ELECTRICAL COMPONENT LOCATIONS table. Measure resistance between kickdown switch connector terminals. If there is no continuity, kickdown switch is adjusted. If there is continuity, adjust kickdown switch. Refer to KICKDOWN SWITCH in the appropriate ADJUSTMENTS article. If continuity is still not as specified after adjustment, replace kickdown switch.

MASS AIRFLOW SENSOR (EXCEPT WITH ECU PART NO. 8A0 906 266B)

  1. Ensure circuit breaker is okay. Disconnect mass airflow sensor connector. See «ELECTRICAL COMPONENT LOCATIONS»(/audi/90/b4-1992-1995/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) table. Turn ignition on. Measure voltage between mass airflow sensor connector terminals No. 2 and 3. (Scheme 27) If battery voltage is not present, check for faulty wiring.
  2. If battery voltage is present, check wiring between mass airflow sensor and ECU. If wiring is okay, push back protective boot on mass airflow sensor connector. Turn ignition on. Measure voltage between mass airflow sensor connector terminals No. 2 and 4.
  3. If 1.0-7.5 volts is not present, replace mass airflow sensor. If 1.0-7.5 volts is present, measure voltage between terminals No. 1 and 2. If 0.3-1.1 volts is not present, replace mass airflow sensor. If 0.3-1.1 volts is present, start engine.
  4. Turn off all electrical accessories. Ensure radiator cooling fan is not running. Vary engine speed between idle and 4000 RPM while measuring voltage between terminals No. 1 and 2. If 1.5-3.4 volts is present, system is okay. If 1.5-3.4 volts is not present, replace mass airflow sensor.

MASS AIRFLOW SENSOR (WITH ECU PART NO. 8A0 906 266B)

  1. Ensure circuit breaker is okay. Disconnect mass airflow sensor connector. See «ELECTRICAL COMPONENT LOCATIONS»(/audi/90/b4-1992-1995/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) table. Turn ignition on. Measure voltage between mass airflow sensor connector terminals No. 2 and 3. (Scheme 27) If battery voltage is not present, check for faulty wiring.
  2. If battery voltage is present, check wiring between mass airflow sensor and ECU. If wiring is okay, push back protective boot on mass airflow sensor connector. Turn ignition on.
  3. Measure voltage between mass airflow sensor connector terminals No. 1 and 2. If 0.3-1.1 volts is not present, replace mass airflow sensor. If 0.3-1.1 volts is present, start engine.
  4. Turn off all electrical accessories. Ensure radiator cooling fan is not running. Vary engine speed between idle and 4000 RPM while measuring voltage between terminals No. 1 and 2. If 1.5-3.4 volts is present, system is okay. If 1.5-3.4 volts is not present, replace mass airflow sensor.

Scheme 27

Scheme 27
Scheme 27

Note. Throttle position sensor is automatically adjusted when throttle position switch is adjusted.

THROTTLE POSITION (TP) SENSOR

  1. Disconnect TP sensor connector. Turn ignition on. Measure voltage between TP sensor connector terminals No. 1 and 2, and terminals No. 1 and 3. (Scheme 28) If 4.5-5.5 volts is not present, check for faulty wiring or ECU.
  2. If 4.5-5.5 volts is present, measure resistance between TP sensor connector terminals No. 1 and 2 (component side). Resistance should be 1500-2600 ohms. With throttle closed, measure resistance between TP sensor connector terminals No. 2 and 3 (component side). Resistance should be 750-1300 ohms.
  3. Slowly open throttle to fully open position. Resistance should increase to 3600 ohms maximum. If resistance is as specified, TP sensor is okay. If resistance is not as specified, replace TP sensor.

Scheme 28

Scheme 28
Scheme 28

Fuel Pump Relay

EGR Control Solenoid Valve

EVAP Control Solenoid Valve

Fuel Injector Solenoid(s)

See FUEL CONTROL .

IAC Valve

FUEL SYSTEM

WARNINGRelieve fuel pressure before disconnecting fuel delivery system components. DO NOT allow fuel to contact engine or electrical components.

FUEL PRESSURE RELEASE

Remove fuel pump relay. See ELECTRICAL COMPONENT LOCATIONS table. 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

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

System Pressure

  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 «ELECTRICAL COMPONENT LOCATIONS»(/audi/90/b4-1992-1995/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) table. 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

  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

Note. Fuel pump connector is accessible through trunk floor.

Fuel Pump Circuit Without Scan Tester (90)

  1. Ensure fuse No. 13 is okay. Refer to the «ELECTRICAL COMPONENT LOCATIONS»(/audi/90/b4-1992-1995/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) table. 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 29) 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)

Remove fuel pump relay. See ELECTRICAL COMPONENT LOCATIONS table. Without voltage applied to relay, there should be no continuity between terminals No. 48 and 52, and between terminals No. 48 and 59. (Scheme 29) 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)

  1. Remove fuse No. 13. See «ELECTRICAL COMPONENT LOCATIONS»(/audi/90/b4-1992-1995/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) table. 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. See article. 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 29)
  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 29)
  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 29

Scheme 29
Scheme 29

Fuel Pump Circuit (100)

  1. Ensure fuse No. 17 is okay. Refer to the «ELECTRICAL COMPONENT LOCATIONS»(/audi/90/b4-1992-1995/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) table. 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 30) 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)

Remove fuel pump relay. See ELECTRICAL COMPONENT LOCATIONS table. Without voltage applied to relay, there should be no continuity between terminals No. 30 and 32, and between terminals No. 31 and 32. (Scheme 30) 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 30

Scheme 30: Fuel Pump Relay (100)
Scheme 30: Fuel Pump Relay (100)

Fuel Injectors

  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 31)
  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»(/audi/90/b4-1992-1995/remont/testing-diagnostics/#engine-controls-systemcomponent-tests__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 «ELECTRICAL COMPONENT LOCATIONS»(/audi/90/b4-1992-1995/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) table.

Fuel Injector Leakage & Volume

  1. Ensure fuel system pressure is okay. See BASIC DIAGNOSTIC PROCEDURES 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

  1. Disconnect O2 sensor heating element connector. See the «ELECTRICAL COMPONENT LOCATIONS»(/audi/90/b4-1992-1995/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) table. 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 31

Scheme 31
Scheme 31

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

  1. Disconnect oxygen sensor connector. Refer to the «ELECTRICAL COMPONENT LOCATIONS»(/audi/90/b4-1992-1995/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) table. 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.

IDLE AIR CONTROL (IAC) VALVE (IDLE STABILIZATION SYSTEM)

  1. Disconnect electrical connector from Idle Air Control (IAC) valve (stabilizer valve). See «ELECTRICAL COMPONENT LOCATIONS»(/audi/90/b4-1992-1995/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) table. Measure resistance between IAC valve connector terminals. If resistance is not 7-11 ohms, replace IAC valve. If resistance is 7-11 ohms, remove IAC valve.
  2. Looking through hole in IAC, check for scored rotary slide valve. Replace IAC valve if rotary slide valve is scored. If rotary slide valve is okay, reconnect IAC valve connector. Turn ignition on. Initiate Output DTM. See OUTPUT DTM in the «TESTS W/CODES»(/audi/90/b4-1992-1995/remont/testing-diagnostics/#engine-controls-self-diagnostics) article. Observe rotary slide valve when IAC valve is activated during Output DTM.
  3. If rotary slide valve travels freely from stop to stop, system is okay. If rotary slide valve shows signs of movement but does not travel freely from stop to stop, replace IAC valve. If rotary slide valve is not activated during Output DTM, check wiring. If wiring is okay, replace ECU.

POWER OUTPUT STAGE

  1. Disconnect power output stage 4-pin connector. See «ELECTRICAL COMPONENT LOCATIONS»(/audi/90/b4-1992-1995/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) table. 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

Disconnect ignition coil 3-pin connector. Refer to the ELECTRICAL COMPONENT LOCATIONS table. 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 32) If resistance is not 0.5-1.0 ohm, replace appropriate coil.

Scheme 32

Scheme 32: IGNITION COIL PRIMARY RESISTANCE
Scheme 32: IGNITION COIL PRIMARY RESISTANCE

IGNITION COIL PRIMARY VOLTAGE SUPPLY

Turn ignition on. Disconnect ignition coil 3-pin connector. See ELECTRICAL COMPONENT LOCATIONS table. 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

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.

TIMING CONTROL SYSTEMS

Note. Information is not available from manufacturer.

  1. Disconnect harness connector from EGR control solenoid valve. See «ELECTRICAL COMPONENT LOCATIONS»(/audi/90/b4-1992-1995/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) table. Measure resistance across EGR control solenoid valve terminals. If resistance is not 25-35 ohms, replace EGR control solenoid valve.
  2. If resistance is 25-35 ohms, connect LED Tester (US 1115) between engine ground and EGR control solenoid valve connector terminal No. 1 with jumper from Adaptor Kit (VW 1594). (Scheme 31) Operate starter for several seconds. If LED does not come on, check circuit breaker, wiring and fuel pump relay.
  3. If LED comes on, connect LED tester between EGR control solenoid valve connector terminals with jumper from adaptor kit. In self-diagnostics mode, initiate Output Diagnostic Test Mode (Output DTM). LED tester should flash when Output DTM is initiated for EGR control solenoid valve.
  4. If LED flashes as specified, system is okay. If LED does not flash as specified, check wiring harness. If wiring harness is okay, replace ECU.

EGR Temperature Sensor

  1. Disconnect EGR temperature sensor connector. See the «ELECTRICAL COMPONENT LOCATIONS»(/audi/90/b4-1992-1995/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) table. Turn ignition on. Measure voltage between EGR temperature sensor connector terminals. If 4.5-5.0 volts is not present, repair faulty wiring or replace ECU as necessary.
  2. If 4.5-5.0 volts is present, turn ignition off. Remove EGR temperature sensor. Set ohmmeter to 200,000-ohm scale. Place EGR temperature sensor in boiling water. Measure resistance across EGR temperature sensor terminals. If resistance changes, EGR temperature sensor is okay. If resistance does not change, replace EGR temperature sensor.
  1. Disconnect EVAP control solenoid valve connector. See the «ELECTRICAL COMPONENT LOCATIONS»(/audi/90/b4-1992-1995/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) table. Measure resistance across EVAP control solenoid valve terminals. If resistance is not 20-28 ohms, replace EVAP control solenoid valve.
  2. If resistance is 20-28 ohms, connect LED Tester (US 1115) between engine ground and EVAP control solenoid valve connector terminal No. 1 with jumper from Adaptor Kit (VW 1594). (Scheme 31) Operate starter for several seconds. If LED does not come on, check circuit breaker, wiring and fuel pump relay.
  3. If LED comes on, connect LED tester between EVAP control solenoid valve connector terminals with jumper from adaptor kit. Initiate Output DTM. LED tester should flash when Output DTM is initiated for EVAP control solenoid valve.
  4. If LED flashes as specified, system is okay. If LED does not flash as specified, check wiring harness. If wiring harness is okay, replace ECU.

THROTTLE CONTROLS

Note. Information is not available from manufacturer.

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