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.
Automatic Climate Control System, On Board Diagnostic (OBD): Function
The AC control head -E87- is a equipped with a DTC memory.
After evaluation, the A/C control head -E87- differentiates between different malfunctions (see DIAGNOSTIC TROUBLE CODE (DTC) TABLE ) and saves those malfunctions until DTC memory is erased.
When malfunctions occur in monitored sensors or components, Diagnostic Trouble Codes (DTCs) are stored in DTC memory with a description of the malfunction type.
Initiate On Board Diagnostic (OBD) at the beginning of the troubleshooting procedure and check DTC memory. To check saved information the following equipment is available:
- VAS 5051 Vehicle Diagnostic, Testing and Information System
- VAG 1551 Scan Tool (ST)
- VAG 1552 Scan Tool
The stored DTCs can be compared to a DTC table with notes regarding potential malfunction causes and specific repair procedures.
- A malfunction will be stored as static malfunction, when a malfunction condition exists longer than a certain (predetermined) time. The malfunction will stored as a sporadic DTC, if the malfunction condition no longer exists in a predetermined time. The procedure repeats itself constantly. Sporadically occurring malfunctions are identified via indication of "ISP" on the display.
- A sporadic malfunction is erased automatically if it no longer occurs after a certain predetermined time.
The full OBD capability can only be accessed via the VAS 5051 Vehicle Diagnostic, Testing and Information System, VAG 1551 Scan Tool or VAG 1552 system tester, using operating mode "Rapid Data Transfer".
The On Board Diagnostic (OBD) is not just limited to saving, checking and erasing DTCs or to output diagnostic test mode, but also can set basic settings, perform control module identification and input coding as additional options.
Operating mode -2- (blink code output) is not available for A/C heating electronics. Operating modes -3- (self test) and -4- can be used by the VAG 1551 Scan Tool or VAG 1552 system tester and are described in the relevant operating manuals.
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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.