Here is a document on how to repair JCB equipment K4718 trouble code intake manifold pressure drop too high at cranking.More repair case for JCB,please refer to:JCB Trouble Repair
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The measured intake manifold pressure (the signal from the boost pressure sensor) is below the warning limit during engine cranking.
Possible causes are:
The engine air supply is clogged.
The boost pressure sensor wiring is defective.
The boost pressure sensor is defective.
Reaction in EEM
The FC is stored and the warning lamp is activated. The CAN message indicates active fault.
NOTE:The engine may not start, or it starts slowly and runs poorly.
Solution
Check the engine air supply system completely, consult the service instructions if necessary.
Check the air filter.
Check the piping from the air filter to the turbocharger (look for obstacles in the joints, the bends).
Check the turbocharger.
Check the piping from the turbocharger to the charge air cooler (look for obstacles in the joints, the bends).
Check the charge air cooler.
Check the piping from the charge air cooler to the inlet manifold (look for obstacles in the joints, the bends).
To check the electrical defects, check the boost pressure sensor, the sensor wiring and the controller input: First save the error log and then erase it. Restart the ECU after erasing the error log. If the fault occurs again during the next driving cycle, check the following paths:
Check the boost pressure sensor wiring, the connectors and the contact surfaces of the connector pins (possible oxidation).
Check the operation with another boost pressure sensor to see if the boost pressure sensor is defective.