Unable to start car U1308 & U1208 communication fault

[GrandpICASSO]

Hi everyone, first time posting here and hoping for some advice.

Car: Citroën C4 Grand Picasso (2017) 1.6 HDi Automatic
Mileage: 225,525 miles
Maintenance: Timing belt at ~210k miles, serviced every 10k miles.

The car has been running fine until recently. One day it struggled to start. After several attempts it eventually started. When shifting from P → D there was a loud clunk, but I was still able to drive it home normally with no loss of power and smooth gear changes, even up to motorway speeds (70mph).

The next morning the car would not start again. It powered on, but would not crank/start fully. AA came out and mentioned the battery was weak. After he sprayed some brake cleaner into the intake, the engine started. Using the diagnostic tool, the main recurring fault codes were:

• U1308
  
  U1208
  
  P0502

The AA technician suggested two possible issues:

Starting issue – He suspects a possible injector fault (perhaps one injector over-fuelling).

Communication issue – Fault in communication between ECU and other modules.

For context: A few months ago the car had speed sensor / ESP / hill start faults (codes: U200, U223, C003A). The mechanic made a temporary repair which resolved those warning lights and the car has driven normally since. He mentioned it was a wiring issue where one of the connections was faulty due to water ingress.

Any guidance on:

Whether the injectors are the likely cause of the hard start,

And whether the communication faults could be related to the previous speed sensor wiring repair

[mickthemaverick]

I think a read through this thread might give you some ideas of where to start looking.

[GrandpICASSO]

I think a read through this thread might give you some ideas of where to start looking.

The issue has now been identified and resolved. The problem was caused by the crankshaft position sensor receiving incorrect signals due to damage to the crankshaft timing reluctor ring (timing pick-up ring). The missing/damaged teeth on the reluctor ring were causing the ECU to read incorrect RPM / TDC reference, which is why the car struggled to start and produced multiple communication and speed-related fault codes.

The following parts were replaced:

• Crankshaft position sensor
  
  Timing reluctor ring (pick-up ring)
  
  Crankshaft pulley

After replacement, the engine signal returned to normal and the car starts and drives correctly again.

Cost Breakdown:

• Diagnosis / initial fault check: £75
  
  Labour for repair: ~£300
  
  Parts (pulley, reluctor ring, crank sensor): ~£200
  
  Total: ~£600

Car is now running fine again.

[wurlycorner]

Glad you got it sorted and thanks for feeding back - always helpful info for others in future.