Engine Controls - System/component Tests Audi A4 B5

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 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.

Note. For systems and components not covered in this article, enter self-diagnostics. See INTRODUCTION in TESTS W/CODES article. Testing is incorporated in self-diagnostic information.

CLOSED THROTTLE POSITION (CTP) SWITCH

Note. Closed Throttle Position (CTP) switch is located within Throttle Position (TP) sensor. By adjusting CTP switch, TP sensor is automatically adjusted.

1. Remove noise dampener and disconnect harness connector from throttle body assembly. Using DVOM, measure resistance between TP sensor terminals No. 4 and 6. (Scheme 24) Resistance must be zero ohms. Open throttle slightly. Resistance must be infinite. If specified resistance is not obtained or is obtained only after opening throttle further, adjust CTP switch.
2. To adjust CTP switch, remove throttle body assembly. Loosen both TP sensor screws. Turn TP sensor counterclockwise until stop is reached. Ensure linkage is not moved. Tighten TP sensor screws in this position. Install throttle body and adjust accelerator pedal cable. See «ADJUSTMENTS»(/audi/a4/b5-1994-1999/remont/adjustments/#engine-controls-adjustments) article.
3. Check CTP switch again. If specified resistance value is still not obtained, replace TP sensor.

Scheme 24

FUEL SYSTEM

FUEL PRESSURE RELEASE

Remove fuel pump relay. Start engine. Allow engine to run until it stalls. 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. Reinstall fuel pump relay.

FUEL PRESSURE TEST

Note. Volkswagen Audi Group (VAG 1551) scan tool is necessary to activate fuel system for fuel pressure test.

Fuel System Pressure

1. Ensure fuel pump relay is okay. Ensure correct fuel filter is installed. Ensure battery voltage is at least 12 volts. Release fuel pressure. Ensure ignition is off.
2. Connect Pressure Gauge (VAG 1318) between fuel supply and fuel return lines in engine compartment. Disconnect and plug vacuum line from fuel pressure regulator. Following VAG 1551 scan tool manufacturer's instructions, energize fuel system.
3. Fuel pressure should be 55-61 psi (3.8-4.2 bar). If fuel pressure is within specification, perform FUEL SYSTEM RESIDUAL PRESSURE test. If fuel pressure is not within specification, replace fuel pressure regulator and perform test again.
4. If fuel pressure is not within specification after replacing fuel pressure regulator, check for damaged fuel pump or damaged fuel lines. Repair as necessary. If fuel pressure is more than specification after replacing fuel pressure regulator, check fuel return line for damage. Repair as necessary.

Fuel System Residual Pressure

1. Tee fuel pressure gauge into fuel supply line. Start engine and let it idle. With cold engine, minimum residual fuel pressure specification is 32 psi (2.2 bar). With hot engine, minimum residual fuel pressure specification is 44 psi (3.0 bar).
2. If residual fuel pressure is minimum or more, residual fuel pressure is okay. If residual fuel pressure is less than minimum, check fuel lines for leaks and repair as necessary. Check fuel injectors for leaks. See «FUEL INJECTOR TEST»(/audi/a4/b5-1994-1999/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) . Check fuel pump check valve for malfunction. See «FUEL PUMP CHECK VALVE TEST»(/audi/a4/b5-1994-1999/remont/testing-diagnostics/#engine-controls-systemcomponent-tests__fuel-pump-check-valve-test) .

Fuel Injector Leak Test

1. Ensure fuel system pressure is within specification before performing this test. Remove fuel rail complete with fuel injectors from engine. DO NOT disconnect fuel supply or return lines. Using VAG 1551 scan tool, energize fuel pump.
2. With fuel pump running, visually inspect fuel injector for leaks. Maximum allowable leakage is 1-2 drops of fuel per injector per minute. If fuel injector leaks more than 2 drops of fuel per minute, replace leaking fuel injector. ALWAYS replace fuel injector "O" rings.

Fuel Injector Resistance Test

Turn ignition off. Disconnect fuel injector electrical connector. Using a DVOM, measure resistance across fuel injector terminals. See INJECTOR RESISTANCE table. If resistance is not within specification, replace fuel injector.

INJECTOR RESISTANCE

Fuel Injector Quantity Test

1. Remove fuel rail, complete with fuel injectors, from engine. DO NOT disconnect fuel supply or return lines. Place fuel injector being tested into a graduated container. Connect one terminal of fuel injector to battery positive terminal.
2. Connect other terminal of fuel injector to ground for exactly 30 seconds. Fuel quantity should be 2.9-3.7 oz. (85-110 ml). If fuel quantity is more than or less than specification, replace faulty fuel injector.

FUEL PUMP CHECK VALVE TEST

1. Connect Pressure Gauge (VAG 1318) between fuel supply and fuel return lines in engine compartment. Ensure pressure gauge test valve is in OPEN position.
2. Operate remote control switch for approximately 30 seconds. Move pressure gauge test valve to CLOSED position. Briefly operate remote control switch until maximum of 80 psi (5.5 bar) is indicated. Observe pressure drop on fuel pressure gauge.
3. After 10 minutes, maximum allowable pressure drop is 7 psi (.5 bar). If pressure drop is more than allowable maximum, ensure no fuel leaks are present in fuel lines. If no fuel leaks are present in fuel lines, fuel pump check valve is defective. Replace fuel pump.

FUEL PUMP RELAY

1. Fuel pump relay is located in position No. 6 of central electrical panel located under left side of the instrument panel. (Scheme 25) Remove cover from end of left side of dashboard. Remove fuses No. 28, 29 and 34.
2. Connect VAG 1527B voltage tester between either terminal for fuse No. 28 and ground. Briefly operate starter motor. Fuel pump relay must audibly click and be felt energizing. Also voltage tester should light up. If fuel pump relay does not operate, go to step 9). If voltage tester does not light up, go to next step.
3. Connect voltage tester to other terminal for fuse No. 28. Repeat step 2). If voltage tester still does not light up, repair wiring harness between fuse No. 28 and terminal No. 30 of fuel pump relay connector. (Scheme 25) Go to next step.
4. Connect VAG 1527B voltage tester between one terminal for fuse No. 29 and ground. Using VAG 1551 scan tool, use OUTPUT DIAGNOSTIC TEST mode, function 03 to trigger fuel pump relay. Voltage tester should light up. If voltage tester lights up, go to step 6). If voltage tester does not light up, go to next step.
5. Connect voltage tester between other terminal for fuse No. 29 and ground. Using VAG 1551 scan tool, use OUTPUT DIAGNOSTIC TEST mode, function 03 to trigger fuel pump relay. Voltage tester should light up. If voltage tester lights up, go to next step. If voltage tester still does not light up, repair wiring harness between fuse No. 29 and terminal No. 30 of fuel pump relay connector. (Scheme 25) Go to next step.
6. Connect VAG 1527B voltage tester between one terminal for fuse No. 34 and ground. Using VAG 1551 scan tool, use OUTPUT DIAGNOSTIC TEST mode, function 03 to trigger fuel pump relay. Voltage tester should light up. If voltage tester lights up, go to step 8). If voltage tester does not light up, go to next step.
7. Connect voltage tester between other terminal for fuse No. 34 and ground. Using VAG 1551 scan tool, use OUTPUT DIAGNOSTIC TEST mode, function 03 to trigger fuel pump relay. Voltage tester should light up. If voltage tester lights up, go to next step. If voltage tester still does not light up, repair wiring harness between fuse No. 34 and terminal No. 31 of fuel pump relay connector. (Scheme 25) Go to next step.
8. Remove fuel pump relay from vehicle. Turn ignition on. Using a DVOM, check voltage between fuel pump relay connector terminals No. 28 and 34, then terminals No. 32 and 34. (Scheme 25) Voltage should be approximately battery voltage. If voltage is not to specification, repair wiring harness as necessary. See «WIRING DIAGRAMS»(/audi/a4/b5-1994-1999/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) section. Test is complete. NOTE: During next step, if voltage tester is left connected for more than one second to relay terminals without operating starter, voltage tester will dimly light (from low current draw).
9. With fuel pump relay removed from vehicle, connect VAG 1527B voltage tester between fuel pump relay connector terminals No. 28 and 29. (Scheme 25) Turn ignition on. Voltage tester should light for approximately one second, then go out. When starter motor is operated, voltage tester should light. If voltage tester operates as specified, replace faulty fuel pump relay. If voltage tester does not operate as specified, go to next step.
10. Turn ignition off. Disconnect Powertrain Control Module (PCM) connectors. Connect VAG 1598/19 test box to PCM wiring harness. Terminal assignments of test box are identical to PCM connectors "A", "B", "C", "D" and "E".
11. Using a DVOM, check resistance between fuel pump relay connector terminal No. 29 and test box socket A5. Maximum resistance is one ohm. If resistance is within specification, replace faulty Powertrain Control Module (PCM). If resistance is not within specification, repair open circuit as necessary. See «WIRING DIAGRAMS»(/audi/a4/b5-1994-1999/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) section.

Scheme 25

IGNITION SYSTEM

Note. Perform spark test before performing other ignition checks.

SPARK TEST

Note. When ignition coil is triggered, spark is supplied to 2 spark plugs at one time. One spark plug fires during compression stroke and the other plug fires during exhaust stroke (waste spark).

Check for a strong Blue spark at coil wire and at each spark plug wire by holding wire terminal no more than 1/4" from chassis ground while cranking engine. Disconnect and inspect all related ignition system connectors and harness. Clean or repair as necessary.

Checking Voltage Supply

1. Turn ignition off. Disconnect Camshaft Position (CMP) sensor 3-pin connector. CMP sensor is located at rear of left cylinder head. Turn ignition on. Connect a DVOM between CMP sensor connector terminals No. 1 and 3. (Scheme 26)and (Scheme 28).
2. Voltage should be 9 volts. If voltage is not to specification, repair open or short in wiring harness between CMP sensor connector and Powertrain Control Module (PCM). See «WIRING DIAGRAMS»(/audi/a4/b5-1994-1999/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) section.

Scheme 26

Checking Resistance

1. Disconnect Crankshaft Position (CKP) sensor connector (located on left side of cylinder block). Using a DVOM, measure resistance between CKP sensor connector (sensor side) terminals No. 1 and 2. (Scheme 27)
2. Resistance should be approximately 1000 ohms. If resistance is not to specification, replace CKP sensor. If resistance is to specification, go to next step.
3. Connect DVOM between CKP sensor connector (sensor side) terminals No. 1 and 3, then terminals No. 2 and 3. Resistance should be infinite (open). If resistance readings are not infinite, replace CKP sensor.

Scheme 27

Ignition Coil Primary Resistance

Disconnect ignition coil 3-pin connector (located in front of intake manifold). Disconnect ignition coil power output stage 3-pin connector (located on right side of engine compartment). (Scheme 28) Measure resistance between any terminal of ignition coil 3-pin connector and power output stage 3-pin connector terminal No. 3. (Scheme 26)and (Scheme 27). Maximum allowable resistance is 5 ohms. If resistance is not within specification for any coil, replace ignition coil assembly.

Scheme 28

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.

Ignition Coil Voltage Supply

Ensure fuse for ignition coils is okay. Turn ignition off. Disconnect White ignition coil voltage supply connector. (Scheme 29), 10 or 11. Turn ignition on. Using a DVOM, measure voltage between ground and all 3 terminals of White ignition coil voltage supply connector. Voltage should be approximately battery voltage. If voltage is not to specification, repair wiring harness as necessary.

Scheme 29

Note. Before performing this test, ensure fuses for ignition coils are okay and ignition coil resistance is okay.

Ignition Coil Output Stage Voltage Check

Disconnect power output stage 3-pin connector (located on right side of engine compartment). (Scheme 28) Turn ignition on. Using a DVOM, measure voltage between each connector terminal and ground. Voltage should be approximately battery voltage. If voltage is not to specification, repair wiring harness as necessary.

Ignition Coil Output Stage Ground Check

Disconnect power output stage 4-pin connector (located on right side of engine compartment). (Scheme 28) Turn ignition on. Using a DVOM, measure voltage between power output stage 4-pin connector terminal No. 2 and battery voltage. (Scheme 30) Voltage should be approximately battery voltage. If voltage is not to specification, repair wiring harness as necessary.

Scheme 30

Wiring Diagram (A4 2.8L - 1 Of 2). Scheme 31

Wiring Diagram (A4 2.8L - 2 Of 2). Scheme 32

See also:
• TESTS W/CODES
• ADJUSTMENTS
• FUEL INJECTOR TEST
• FUEL PUMP CHECK VALVE TEST