4.0      PROBLEM: Pressure drops down to Zero when vehicle is parked
4.1	Dual brake valve Relay valve - if fitted.	Leak through exhaust.	Overhaul assy.*
4.2	Hose, pipes & fittings	Leakage from SPV delivery line circuits with internal in System Protection Valve assembly.	Identify and rectify the leaky joints. Replace hose assy. If damaged. Check SPV for internal leak and overhaul assy., * if defective . (If no internal leak, check delivery line circuits of 21 & 22 only.)
4.3	System protection valve (SPV)	External leak from the SPV assembly.	Overhaul assy.*
4.4	Service reservoirs	Leakage through weld joints and drain valve.	Rectify weld joint. Replace defective drain valve.