Checking exhaust gas recirculation valve N18 - vehicles with engine code letters AJM — AUDI

🧭 Before you start

Unplug N18 and measure its resistance; renew the valve if out of tolerance. Check supply voltage with the ignition on and repair any open circuit. Connect a voltage tester across the contacts and actuate N18 through final control diagnosis. If it does not respond, connect the test box to the harness with the control unit disconnected and check the wiring for open circuit and shorts to positive or earth.

Fits: Audi A6 C5 (4B)

• Special tools named: V.A.G 1526

Don't miss

• Judge the resistance reading against engine temperature; cold reads low, hot reads high.
• A low-draw voltage tester may glow between pulses rather than going out fully.
• Leave the engine control unit disconnected when the test box is fitted.
• Select the right meter range before connecting leads to avoid damaging electronics.

Written for this job from the workshop steps below · TorqFix editorial.

🔧 Engine codes this applies to

📐 49 workshop diagrams for AJM

Real factory drawings for this job — timing marks, bolt locations and routing. Locked in the free view.

📋 Procedure

1. Disconnect connector (1) from exhaust gas recirculation valve N18(Item 2).
2. Connect hand-held multimeterV.A.G 1526 A or V.A.G 1526 B to valve to measure resistance. [Note: At room temperature the resistance is in the lower tolerance range; at operating temperature it is in the upper tolerance range.]
3. Renew exhaust gas recirculation valve N18.
4. Connect hand-held multimeterV.A.G 1526 A or V.A.G 1526 B to contact (2) and earth to measure voltage.
5. Switch on ignition.

6. Check for open circuit in wiring (see current flow diagram) and repair if necessary.
7. Connect voltage testerV.A.G 1527 B between contacts (1) and (2).
8. From the selection menu (1) select the diagnostic function "“03 - Final control diagnosis”".
9. Press the button → repeatedly until the exhaust gas recirculation valve N18 is actuated. [Note: Voltage testers with a low current draw do not go out completely between activation signals from engine control unit, but continue to glow slightly and become distinctly brighter on activation.]
10. Press the ← button to exit from function "“03 - Final control diagnosis”".
11. Press "“06 - End output”".
12. Switch off ignition.
13. Connect test boxV.A.G 1598/31 to connectors of wiring harness; do not connect engine control unit. Connect earth clamp of test box to earth (not shown in illustration) TDI injection and glow plug system (4-cyl.)23.
14. ⚠ To prevent damage to electronic components, select appropriate measuring range before connecting measuring leads and observe test requirements. — Check for open circuit and short to positive or earth in the following wiring:
15. Repair wiring connection if necessary.

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