How Opus IVS Diagnosed and Solved a No-Start Fault
When a modern vehicle suddenly refuses to start, the problem can often be traced back to the smallest detail. The following is an example of how Opus IVS Master Technician Ben Palmer quickly restored a 2025 Volkswagen Crafter to complete working order for a garage customer.
The Challenge
A 2025 Volkswagen Crafter arrived at William Galloway garage after failing to start following the fitting of a towbar. When the ignition was switched on, the dashboard displayed “Key Not Detected”, and the vehicle remained completely unresponsive.
Background
Before the towbar installation, the van had already undergone a tracker installation by a third-party company. The job reportedly took several hours, with the installers struggling to complete the setup.
Afterwards, when the garage fitted the towbar and reconnected the battery, the Crafter would not start. The issue appeared immediately, a clear indication that a communication fault had been introduced somewhere in the electrical system.
Initial Findings
When Ben Palmer began his investigation, he noted the following:
The no-start condition occurred immediately after the battery was disconnected and reconnected.
Diagnostics could communicate only with the Gateway, TPM, and Park Aid modules.
• Faults were logged for “No communication with Park Aid” and another ECU.
• The J519 Body Control Unit (BCU) wiring appeared physically sound.
• A previously damaged connector C pin 58 (brake-light signal) had been repaired.
Ben suspected interference from the tracker or a CAN bus wiring fault, which connects all major control modules.
Diagnosis and Discovery – VW Crafter No-Start Fault
Working with the customer, Ben traced the wiring at the J519 Body Control Module.
Inside plug A, he found the crucial error — pins 20 and 21, which carry CAN High and CAN Low signals, had been reversed.
This reversal disrupted the vehicle’s CAN communication network, preventing modules like the immobiliser and key-detection system from communicating. Essentially, the van could no longer “see” its own key.
VW Crafter No-Start Fault – The Fix
After carefully swapping pins 20 and 21 back to their correct positions, the transformation was immediate:
The vehicle started normally.
The “Key Not Detected” warning cleared.
All communication faults were resolved.
The customer expressed sincere thanks to Ben and the Opus IVS team for their expertise and support.
Root Cause
Fault: Reversed CAN High/Low wiring in plug A of the J519 Body Control Unit
Effect: Total CAN communication failure, disabling the immobiliser and key-recognition system
Outcome
• Vehicle started and operated normally
• All faults cleared
• Customer fully satisfied with the resolution
Key Takeaways
This case highlights the importance of thorough wiring checks and diagnostic precision when dealing with communication faults:
• Always verify CAN bus integrity after third-party installations such as trackers, alarms, or towbar electrics.
• Reversed CAN wires can lead to total communication loss and immobiliser-related “Key Not Detected” messages.
• Before replacing expensive components, inspect recent wiring work, it’s often where the problem begins.
Conclusion
In this Volkswagen Crafter 2025, a simple wiring reversal caused a complete immobilisation. Thanks to expert diagnostics and a structured approach, Opus IVS quickly identified the issue, corrected the wiring, and got the customer back on the road.
At Opus IVS, we empower workshops with the tools, training, and live technical support needed to diagnose complex electrical and communication faults efficiently, with no guesswork and no unnecessary part replacements.
Need Help Diagnosing a No-Start or CAN Bus Fault?
If you’re facing “Key Not Detected,” “No Start,” or communication issues after an installation, Opus IVS can help.
Our expert technicians provide advanced diagnostic support and live technical assistance to workshops across the UK and beyond.
Get in touch with the Opus IVS team today to learn how our diagnostic solutions and remote support can help you resolve complex faults faster.