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.
A/C system, On Board Diagnostic (OBD): Function
The A/C Control Head -E87 receives from the electrical and electronic components (information senders) information that is processed according to the specified values.
The output signals of the control module then control the electrical components (actuators).
In order to determine component or open wiring malfunction cause quickly, the AC Control Head -E87 is equipped with a DTC memory, the memory can be checked with scan tool VAG 1551, Vehicle Diagnostic System VAS 5051 or scan tool 1552. On vehicles starting at model year 2002 only in conjunction with VAS 6017 adapter.
When malfunctions occur in monitored sensors or components, Diagnostic Trouble Codes (DTCs) are stored in DTC memory with a description of the malfunction type.
To begin troubleshooting, initiate On Board Diagnostic (OBD) and read out stored data using the:
VAG 1551 Scan Tool (ST)
the VAG 1552 Vehicle system tester
Or the VAS 5051 Vehicle Diagnostic, Testing and Information System
The indicated diagnostic data leads to a DTC table with notes regarding potential malfunction causes and specific repair procedures.
Notes for malfunction treatment
- The data output is only possible with the ignition switched on or with the engine running and the RPM must be less than 3000 RPM. The data output is limited or will be aborted when the RPM is greater (the output Diagnostic Test Mode (DTM) is only possible to an RPM upon 3000 RPM, the DTM will be aborted when this RPM is exceeded.
- The DTM will be aborted as soon as the vehicle moves faster than 5 km/h, the display indicates "Function unknown or cannot be carried out at the moment".
- A malfunction will be stored as static malfunction, when a malfunction condition exists longer than a certain (predetermined) time. The malfunction will change to 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 "/SP" on the right-hand side of the display.
- A sporadic malfunction is erased automatically if it no longer occurs after a certain time.
The full potential of On Board Diagnostic (OBD) can only be achieved using the VAG 1551 Scan Tool (ST), operating mode 1 "Rapid Data Transfer", VAG 1552 and the VAS 5051.
The On Board Diagnostic (OBD) is not just limited to saving, checking and erasing or output diagnostic test mode, but also offers with basic setting, control module identification and coding additional options.
Operating mode -2- (blink code output) is not available with climate control/heating electronic. The operating modes -3- (self test) and -4- pertain only to scan tool VAG 1551 or vehicle system tester VAG 1552 and are described in the relevant operating manuals.
The OBD can be carried out in the same fashion using VAS 5051 or VAG 1552. After checking the DTC memory it is helpful to print out the stored malfunction, this helps to answer possible questions at a later point. If the DTC memory was checked with the VAG 1552, connect VAG 1551 or VAS 5051 in order to print stored malfunction before erasing DTC memory (VAG 1552 is not equipped with a printer).
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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.