Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSAUDI1998A4 AVANT QUATTRO, AUTOMATICREPAIR AND DIAGNOSISHEATING, VENTILATION & A/C (HVAC)HVAC CONTROL SYSTEMSA/C-HEATER SYSTEMTESTINGA/C-HEATER CONTROL PANEL
1998 Audi A4 Avant Quattro, Automatic
A/C-Heater Control Panel
1998 Audi A4 Avant Quattro, AutomaticSECTION A/C-Heater Control Panel
- Put DVOM in 20-volt range. Using Adapter Cable (VAG 1598/12), use DVOM to check voltage between Test Box (VAG 1598) terminals No. 9 and 14. Turn ignition on. If battery voltage does not exist, check Black/Blue or Brown/Blue wire between fuse block and A/C-heater control panel. Check Brown wires between A/C-heater control panel and ground. Repair as necessary.
- Check voltage between test box terminals No. 9 and 15. Turn ignition on. If battery voltage does not exist, check Brown wires between A/C-heater control panel and ground. Repair as necessary.
- Using Adapter Cable (VAG 1589/11), connect test leads between test box terminal No. 33 and ground. Turn ignition on. Using LED Tester (US 1115), ensure LED in tester comes on. If LED does not come on, repair open or short circuit. See WIRING DIAGRAMS . If LED comes on, go to next step.
- Ensure test leads are still connected to test box terminal No. 33 and ground. Start engine. If LED does not flicker briefly, then light steady, check voltage signal from instrument cluster. See WIRING DIAGRAMS .
- Check voltage between test box terminal No. 7 and ground. Turn ignition on. Turn parking lights on. If about battery voltage does not exist, check wiring between headlight switch and A/C-heater control panel. Repair as necessary.
- Check voltage between test box terminal No. 7 and ground. Turn ignition on. Turn parking lights off. If greater than 2 volts is present, repair short to voltage in wiring between headlight switch and A/C-heater control panel.
- Check voltage between test box terminal No. 45 and ground. Turn ignition on. Turn parking lights on. When illumination rheostat is turned, voltage should fluctuate between zero and 12 volts depending on setting. If voltage is not as specified, check wiring between headlight switch and A/C-heater control panel. Repair as necessary.
- Check voltage between test box terminal No. 45 and ground. Turn ignition on. Turn parking lights off. If greater than 2 volts is present, repair short to power in wiring between headlight switch and A/C-heater control panel.
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When to See a Mechanic
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.