This article documents the troubleshooting process of A/C issues in a 2015 Volkswagen Golf using VCDS (Vag-Com Diagnostic System). The primary focus is on potential problems with the A/C pressure sensor (G805) and the related diagnostic procedures. The goal is to determine if a faulty G805 sensor is causing the A/C compressor to shut down intermittently.
Initial Diagnosis and Testing with 2015 Golf VCDS
Initial readings from Measuring Value Blocks (MVB) in VCDS with the key on, engine off (KOEO) showed inconsistent pressure readings compared to manual gauge measurements. With the A/C off, the MVB displayed 8.6 bar, while with the A/C on, it showed 14.2 bar. However, direct pressure readings indicated significantly different values. Suspecting a faulty G805 sensor, further tests were conducted.
Further KOEO tests revealed a consistent MVB reading of 2.2 bar regardless of actual high and low side pressure readings. This discrepancy further pointed towards a potential issue with the G805 sensor. Three different G805 sensors were tested, all yielding similar inaccurate results.
Testing Procedures and Results
To isolate the problem, the following tests were performed:
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Disconnected G805 Test: With the original and a replacement G805 disconnected from the liquid line but still connected electrically, the MVB readings were 0.8 bar and 1.0 bar respectively. The 0.8 bar reading from the original sensor aligned with the expected pressure at the vehicle’s elevation (2800 ft).
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Bypass Harness Test: The wiring between the G805 and the HVAC module (J301) was bypassed by cutting and splicing the violet/blue wire (pin 16 on connector T20D). This test yielded no change in the MVB reading (2.2 bar), suggesting the wiring harness was not the culprit.
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Disconnected Signal Wire Test: Disconnecting only the signal wire from the G805 while leaving the rest of the harness intact resulted in a 51 bar reading in the MVB. This confirmed that the ECM was responding to changes in the G805 circuit.
HVAC Module Reset Procedures
Before condemning the G805 sensors, potential solutions involving the HVAC module were explored:
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Mitchell Wiring Suggestion: Documentation suggested performing a “Replace Control Module” function, a Basic Setting, and an A/C compressor first start adaptation using VCDS after replacing the J301 module. This was considered a potential “reboot” solution.
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VCDS Reset Functions: Two VCDS reset functions were identified: “IDE01475 – Resetting all adaptations” and “IDE02325 – Reset to factory settings.” The latter resulted in an “ERROR: Request out of range” message. The former has not been tested.
Conclusion and Next Steps
The evidence strongly suggests that the three tested G805 sensors are faulty. The next step is to acquire a genuine VW G805 sensor and retest the system. It is suspected that the aftermarket G805 sensors installed after a previous front-end collision are not meeting VW specifications, causing the intermittent A/C compressor shutdowns. Further investigation into VCDS reset procedures may be warranted if the new OEM sensor does not resolve the issue. The ultimate goal is to restore proper A/C function and understand the system thoroughly to address similar problems in other Volkswagen Golf vehicles.
