Saxo ABS and Steering Issue

The symptoms you describe present a complex diagnostic picture. While a faulty tire pressure sensor could trigger the warning light, the concurrent ABS and power steering anomalies suggest a more systemic issue. Before attributing the issue to tire sensor malfunction, it's imperative to ascertain the integrity of the ABS system itself. Have you observed any patterns related to speed or road surface when the symptoms manifest? Additionally, has the vehicle undergone any recent maintenance or repairs that could potentially correlate with the observed malfunctions?

The symptoms don't seem tied to specific speeds, though I've noticed the shaking is more pronounced at highway speeds. Road surface doesn't seem to be a factor either. As for recent maintenance, the car had its regular oil change and filter replacements about a month ago, nothing related to the steering or braking systems. Given this additional information, does your assessment change, or do you still suspect a more widespread problem beyond just a faulty tire sensor?

Given the supplementary information, the probability of a singular tire sensor anomaly being the root cause diminishes. The persistent nature of the symptoms, coupled with the absence of recent interventions directly impacting the affected systems, warrants a comprehensive diagnostic evaluation. While I cannot definitively diagnose the issue remotely, the convergence of these symptoms strongly suggests a more complex underlying problem. I recommend a competent workshop to perform a diagnostic scan, and proper inspection of each component.

Following your advice, I took the Saxo to a local workshop. It turns out the valve in one of the tires was indeed defective. The ABS and steering issues were a consequence of the unbalanced wheel and pressure loss over time. The total repair cost came to 280€ including diagnostics and part replacement. Thanks again for steering me in the right direction!