Checking Control Function

Select "READING MEASURING VALUE BLOCK" function 08 on (VAG 1551) Scan Tool and input display group 01. See CONNECTING SCAN TOOL (VAG 1551) .

NOTE: A display value OVER 1.04 indicates that the HO2S has detected a lean condition and, to compensate, has enriched the control system. A display value UNDER 0.96 indicates that the HO2S sensor has detected enrichment and to compensate, has created a lean condition.

Observe display value in channel 3. Display must be: 0.96-1.04 volts.
Display must not remain at 1.0 volts (average value): value must fluctuate. If specified value is NOT obtained, check for the following malfunctions:
- Fuel system pressure too high or too low. See FUEL PRESSURE under FUEL SYSTEM in BASIC DIAGNOSTIC PROCEDURES article.
- Leak in intake air system between engine and Mass Air Flow (MAF) sensor. Inspect for vacuum leaks.
- Leak in exhaust system between engine and HO2S probe. Inspect for exhaust leaks.

Fig 1: Identifying Location Of HO2S Signal Control Harness Connectors

Courtesy of AUDI OF AMERICA, INC.