Hi all, just wanted to share my experience in case it helps someone else with a similar issue on their Astra K.

It's a 2016 Vauxhall Astra K 1.4 Turbo (Petrol)

These were my symptoms:

• ABS light, traction control light, and parking brake light came on while driving
• Messages on screen:
  • "Service power steering – drive with care"
  • "Steering assist reduced – drive with care"
• Instrument cluster lost all data – all needles dropped to zero (except fuel) even while driving
• Throttle response was glitchy – it would kick in and cut out sporadically
• Engine remained running despite above symptoms
• Sometimes the faults would clear up on their own, and car would operate normally
• Other times, if I turned off the car while these issues were present, it would not start (no crank)

The issue was unpredictable. Sometimes it occurred 20 minutes into a drive, other times it happened from the moment I entered the car. If present at startup, the car would not crank at all. Because it was so inconsistent, multiple garages couldn’t reproduce or diagnose it reliably.

Initial Diagnosis:

• Battery was replaced (as a precaution) – this did not fix the issue
• Fault codes stored:
  • U0073 – Control Module Communication Bus "A" Off
  • Plus multiple lost communication errors with BCM, ECM, Power Steering, etc.
• This pointed to CANBUS issues but garages couldn’t identify the source

Self-Diagnosis and Fix:
After 9 months of this issue rendering this car barely drivable due to the unreliability of not knowing whether it would start or have issues when driving, one day while the issue was happening on my driveway, I decided to investigate the CAN network myself.

1. Measured resistance across CAN pins on the OBD port:
   • Reading: 120 ohms
   • Expected: 60 ohms (two 60 ohm resistors should be in parallel in a healthy CAN network)
   • Interpretation: One of the terminating resistors was disconnected, suggesting a break or bad connection somewhere in the CANBUS
2. Inspected connections at various modules:
   • Checked the BCM, steering wheel module, etc. – all looked fine
   • Eventually checked the ABS module connector under the coolant expansion tank
     • Disconnected harness and found moisture and corrosion (blue/green discoloration)
     • Cleaned and dried the connector
3. After cleaning and reconnecting the ABS module harness:
   • Resistance at OBD port went back to 60 ohms
   • Car started immediately
   • All fault lights and issues disappeared and the problem never came back

Conclusion:
The root cause was corrosion in the ABS module connector, which disrupted the CANBUS network and caused loss of communication between critical modules like the BCM and ECM. This resulted in the no-start condition and multiple warning messages.

If you're facing similar intermittent issues with dashboard lights, loss of communication errors, and no-crank problems on your Astra K, it’s worth checking the ABS module connector for moisture and corrosion. Measuring the CAN resistance at the OBD port can help narrow down network faults.

Hope this helps someone in the same situation.