One of the biggest challenges when diagnosing any system, is knowing the system layout, and where the components are physically located. A recent call to the Autobiz Technical Helpline brings this to our attention.

A 2019 Audi A5 mHEV presented with a fault code C053D, brake pressure sensor 1. In the initial scan of the serial data, it showed pressure sensor 1 was invalid.

The next step was to locate a diagram for the ABS/ESP system. Unfortunately, this was proving very difficult, to identify the pressure sensors on the OE wiring diagram. From previous cases, we knew they are often located internally, within the ABS modulator assembly (Fig. 1).

The reason the diagram was not readily available, is that the two internal pressure sensors are internally connected between the module and the hydraulic unit. This proved our previous system knowledge, but to prove it on the car the technician was working on, we needed evidence to show the connectivity.

We sent the garage a diagram that showed the location of the pressure sensor contact on the ABS Control Unit (Fig. 2) In this diagram, you can see the connection plate and the pressure sensors located in the modulator assembly.

In previous models, the two sensors could be replaced. Often, a kit was available from the ECU repair companies. But on this model, the sensor pack is integrated into the unit. It is not demountable. The only solution was a new replacement ABS modulator assembly.

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