Engine Controls - Self-Diagnostics - Introduction: Other Audi A4 B5 facelift

MALFUNCTION INDICATOR LIGHT (MIL)

MIL will illuminate if a failure occurs with Powertrain Control Module (PCM) or Transmission Control Module (TCM). If a failure occurs associated with TCM, see appropriate ELECTRONIC CONTROLS article in TRANSMISSIONS.

When ignition is turned on, MIL should come on. When engine is started, MIL should turn off after a couple of seconds. If MIL does not turn off after engine is started, or if MIL comes on while driving, retrieve Diagnostic Trouble Codes (DTCs). See RETRIEVING DIAGNOSTIC TROUBLE CODES .

If MIL lights continuously, a malfunction is present that will cause an increase in emissions. If MIL starts to blink, a malfunction is present which may lead to catalytic converter damage. Repair these failures as quickly as possible. For some failures, MIL is only turned on after failure occurs after 2 successive trips with cold engine starts preceding failure.

Some failures will set a DTC which will never cause MIL to light. An example of a failure that could occur and not cause MIL to light would be a FUEL LEVEL TOO LOW signal generated on a A4 1.8L model.

Note. If MIL is on continuously and no DTCs are stored, perform MIL check. See MIL CHECK. If MIL never illuminates, see MIL CHECK.

HARD FAILURES

Hard failures (also called static malfunctions) cause MIL to come on and a code to set in Powertrain Control Module (PCM) memory. A code that sets as a result of a hard failure will not be erased automatically when the problem is eliminated. These codes must be erased manually.

INTERMITTENT FAILURES

When an intermittent failure occurs, MIL comes on and a Diagnostic Trouble Code (DTC) sets. Powertrain Control Module (PCM) stores DTC as sporadic. Intermittent (sporadic) failures will be erased by PCM if failure does not occur again within 40 engine starts on Cabriolet, or after 50 engine starts with engine reaching operating temperature on 1.8L and 2.8L (except Cabriolet). Intermittent failures may be caused by problems with a sensor, connector or wiring. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES article.

PCM VOLTAGE CHECK

Note. When Powertrain Control Module (PCM) connectors are disconnected, all Diagnostic Trouble Codes (DTCs) will be erased. It is necessary to use VAG 1598 test box and Digital Volt/Ohmmeter (DVOM) to perform voltage check.

Note. It is necessary to generate a PCM readiness code if PCM memory is cleared, battery voltage is disconnected or PCM is disconnected. See CLEARING DIAGNOSTIC TROUBLE CODES under SELF-DIAGNOSTIC SYSTEM.

VOLTAGE CHECK (1.8L TURBO)

1. Turn ignition off. Check fuse for Powertrain Control Module (PCM). Replace as necessary. Disconnect PCM connectors. PCM is located in left rear corner of engine compartment inside electrical box. Connect VAG 1598/22 test box to PCM wiring harness. (Scheme 17)
2. Connect DVOM to test box sockets No. 3 (B+) and 2 (GND). Voltage should be 10-14.5 volts. If voltage is within specification, go to next step. If voltage is not within specification, repair wiring as necessary. See WIRING DIAGRAMS article.
3. Connect DVOM between test box sockets No. 1 (B+) and 2 (GND). Voltage should be 10-14.5 volts. If voltage is within specification, voltage supply is okay. If voltage is not within specification, repair wiring harness as necessary. See WIRING DIAGRAMS article.

VOLTAGE CHECK (A4 2.8L)

1. Turn ignition off. Check fuse for Powertrain Control Module (PCM). Replace as necessary. Disconnect PCM connectors. PCM is located in left rear corner of engine compartment inside electrical box. Connect VAG 1598/22 test box to PCM wiring harness. (Scheme 17)
2. Connect DVOM to test box sockets No. 3 (B+) and 2 (GND). Voltage should be 10-14.5 volts. If voltage is within specification, go to next step. If voltage is not within specification, repair wiring as necessary. See WIRING DIAGRAMS article.
3. Connect DVOM between test box sockets No. 1 (B+) and 2 (GND). Voltage should be 10-14.5 volts. If voltage is within specification, voltage supply is okay. If voltage is not within specification, repair wiring harness as necessary. See WIRING DIAGRAMS article.

Scheme 17

MIL CHECK

Note. When Powertrain Control Module (PCM) connectors are disconnected, all Diagnostic Trouble Codes (DTCs) will be erased. It is necessary to use VAG 1598 test box to perform procedures.

Note. It is necessary to generate a PCM readiness code if PCM memory is cleared, battery voltage is disconnected or PCM is disconnected. See CLEARING DIAGNOSTIC TROUBLE CODES under SELF-DIAGNOSTIC SYSTEM.

Note. MIL check should only be performed if MIL is on continuously and no DTCs are stored or MIL never illuminates.

1. Turn ignition on. MIL should light. If MIL lights, go to step 5). If MIL does not light, go to next step.
2. MIL is not lighting due to faulty wiring or an open circuit. Turn ignition off. Disconnect Powertrain Control Module (PCM) connectors. PCM is located in left rear corner of engine compartment inside electrical box. Connect VAG 1598/22 test box to PCM wiring harness. (Scheme 17)
3. Connect a jumper wire between test box sockets No. 2 and 17. Turn ignition on. MIL should light. If MIL does not light, go to next step.
4. Turn ignition off. Inspect MIL bulb. If bulb is okay, check for an open circuit between MIL and PCM. See WIRING DIAGRAMS article. If wiring is okay, replace faulty PCM. See «PCM REPLACEMENT»(ref-3050-S33466330562000041700000).
5. Start engine and let it idle. MIL should go out after a few seconds. If MIL goes out, MIL is functioning properly. If MIL does not go out, check for any stored DTCs. See «RETRIEVING DIAGNOSTIC TROUBLE CODES»(ref-3050-S23702472112000041700000) under SELF-DIAGNOSTIC SYSTEM. If DTCs are stored, repair as necessary. If no DTCs are stored, go to next step.
6. MIL is on continuously due to a short to ground. Turn ignition off. Disconnect Powertrain Control Module (PCM) connectors. Connect VAG 1598/22 test box to PCM wiring harness. (Scheme 17)
7. Connect a DVOM between test box socket No. 17 and ground. DVOM should indicate infinity (no resistance). If DVOM reading is not as specified, go to next step. If DVOM reading is as specified, go to step 9.
8. Check for a short circuit between MIL and Powertrain Control Module (PCM). See WIRING DIAGRAMS article.
9. If no continuity is present and there is no short to ground, replace faulty PCM. See «PCM REPLACEMENT»(ref-3050-S33466330562000041700000).

PCM CODING

Note. When using Volkswagen Audi Group (VAG) 1551 scan tool, follow manufacturer's instructions for operation. VAG 1551 scan tool is necessary to perform PCM coding.

If Powertrain Control Module (PCM) is replaced, it is necessary to code new PCM. If new PCM is not properly coded, the following problems may occur

1. Driveability problems (i.e., harsh shifting).
2. False malfunctions stored in PCM memory.
3. Increased fuel consumption.
4. Increased exhaust emissions.
5. Reduction in transmission life.
6. All PCM functions are not carried out (i.e., EVAP system operation).

Connect VAG 1551 scan tool to Data Link Connector (DLC). Following manufacturer's instructions, access PCM coding information using VAG 1551 scan tool. For PCM coding options, see appropriate PCM CODING OPTIONS table.

As an example, a properly coded PCM for an A4 model with Front Wheel Drive (FWD) without traction control and 5-speed manual transmission would look like 06001 on the VAG 1551 scan tool.

Note. After coding PCM and starting engine for first time, allow engine to idle for several minutes so PCM can go through a learn function. Idle speed may be erratic while PCM is learning.

PCM CODING OPTIONS (A4)

SUMMARY

If no hard codes (or pass codes only) are present, driveability symptoms exist or intermittent codes exist, proceed to TROUBLE SHOOTING - NO CODES article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.