Testing

A/C Auxiliary Signal Checking: Testing — 1994 Audi S4 Service Manual & Component Testing >> Miscellaneous Controls >> A/C Auxiliary Signal Checking >> Testing A/C Auxiliary Signal Checking: Testing Start engine and let idle. Select "READ MEASURING VALUE BLOCK" function 08 using (VAG 1551) Scan Tool and input display group number 05. See READING/MEASURING VALUE BLOCK (FUNCTION 08) under OUTPUT DIAGNOSTIC TEST MODES (DTM) in SELF-DIAGNOSTICS article. Observe display values in channel 4. Display position 1 indicates if A/C compressor is ON: Must read 0. Display position 2 indicates if A/C system is ON: Must read 0. Display position 3: Must remain blank. Switch ON A/C, selecting lowest temperature and highest blower speed. Observe display values. Position 1 must change from 0 to 1. Position 2 must change from 0 to 1. If positions do not change as described, connect (VAG 1598) test box, using (VAG 1598/5) adapter cable to Engine Control Module (ECM). See CONNECTING VAG 1598 TEST BOX. Connect (US 1115) LED tester between terminal No. 19 (ground) and terminal No. 41. Allow engine to idle. Switch ON A/C, selecting lowest temperature and highest blower speed. LED tester must light up. Idle speed must increase. If LED tester does NOT light up: Switch ignition OFF (stop engine). Wait at least 30 seconds before disconnecting adapter cable from ECM. Check wiring for breaks/opens between ECM terminal No. 41 (terminal 41 of test box), and A/C control head -E87-. See Figure. Also, see WIRING DIAGRAMS. If wiring is Okay, check function of A/C. If A/C function is Okay, replace ECM. After replacement of ECM, see ECM IDENTIFICATION and ECM CODING under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS article.