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HOMESERVICE MANUALSAUDI1996A4 BASE, STANDARDREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCESYSTEMENGINE CONTROLS - TESTS W/CODES - 2.8LCIRCUIT TESTSDTC P1509/17917 - IAC CIRCUIT ELECTRICAL MALFUNCTION
1996 Audi A4 Base, Standard

DTC P1509/17917 - IAC Circuit Electrical Malfunction

1996 Audi A4 Base, StandardSECTION DTC P1509/17917 - IAC Circuit Electrical Malfunction
NOTE: When DTC is set, both power output stages (positive and negative output) are switched off. IAC valve has no power and opens limp-home cross section.
  1. Inspect Idle Air Control (IAC) valve connector for looseness and/or corrosion. IAC valve is located on top right rear corner of engine. Repair connector as necessary. If connector was not repaired, go to next step. If connector was repaired, erase DTC memory and test drive vehicle.
  2. Disconnect Idle Air Control (IAC) valve electrical connector. IAC valve is located on top right rear corner of engine. Using DVOM, check IAC valve resistance. Measure resistance across IAC valve terminals. Resistance should be 7-11 ohms. At room temperature, resistance will be lower. If resistance is measured at underhood operating temperatures, resistance will be higher. Go to next step.
  3. If resistance is within specification, go to next step. If resistance is not with specification, replace IAC valve. Erase DTC memory and test drive vehicle.
  4. Remove IAC valve from engine. Visually inspect surface of rotary slide for signs of wear and/or damage. DO NOT  pry on rotary slide to check for ease of movement. Rotary slide could become damaged (scratched). If rotary slide is not visibly damaged, go to next step. If rotary slide is visibly damaged, replace IAC valve. Erase DTC memory and test drive vehicle.
  5. With IAC valve still off of the engine, reconnect IAC valve electrical connector. Turn ignition on. Using VAG 1551 scan tool, use OUTPUT DIAGNOSTIC TEST mode, function 03 to trigger IAC valve. Check if rotary slide moves freely from stop to stop. If IAC valve does not react to triggering, go to next step. If rotary slide does not move freely (sticks, moves slowly or does not move fully in either direction), replace IAC valve. Erase DTC memory and test drive vehicle. If rotary slide moves freely from stop to stop, IAC valve is functioning properly. Replace faulty PCM. Erase DTC memory and test drive vehicle.
  6. With IAC valve connector connected, push back rubber boot on connector. Connect VAG 1527B voltage tester between IAC valve connector terminal No. 1 and ground. Using VAG 1551 scan tool, use OUTPUT DIAGNOSTIC TEST mode, function 03 to trigger IAC valve. Voltage tester should flash. If voltage tester does not flash as specified, go to step 8). If voltage tester flashes as specified, go to next step.
  7. With IAC valve connector connected, push back rubber boot on connector. Connect VAG 1527B voltage tester between IAC valve connector terminal No. 2 and battery voltage. Using VAG 1551 scan tool, use OUTPUT DIAGNOSTIC TEST mode, function 03 to trigger IAC valve. Voltage tester should light. If voltage tester does not light, go to step 8). If voltage tester lights, circuits are functioning properly. Replace faulty PCM. Erase DTC memory and test drive vehicle.
  8. 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".
  9. Using DVOM, check continuity between IAC valve harness connector terminal No. 1 and test box socket D11, then between terminal No. 2 and test box socket D9. Continuity should be present. If continuity is not present on either or both circuits, repair wiring harness as necessary. See WIRING DIAGRAMS  section. Erase DTC memory and test drive vehicle.
  10. If continuity is present but triggering still does not occur, replace faulty PCM. Code new PCM and test drive vehicle. See PCM CODING  and TEST DRIVE in this article. Recheck DTC memory and verify DTC does not set again. If DTC sets again, perform testing procedure again. If triggering signal and wiring are okay, but IAC valve still does not react, replace IAC valve. Erase DTC memory and test drive vehicle.
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Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.