DTC C1A13-64: Pressure Does Not Decrease When Venting Gallery - Signal plausibility failure: Action

Visually check the gallery pipes for evidence of melting, crushing, kinking or collapsing. If pipes appear sound, disconnect the pipe at both ends and check for free air flow. Repair/renew pipes as required, clear the DTCs and retest
Check the air suspension air supply unit exhaust silencer/exhaust pipe for blockages/restrictions. Repair as required, clear the DTCs and retest
Starting with the vehicle around normal height, using the Jaguar Land Rover Approved Diagnostic Equipment, open the exhaust valve. If the rear suspension height lowers quickly as soon as the exhaust valve is opened then a rear air spring pipe and the front gallery pipe are fitted to the rear valve block incorrectly. Rectify as required, clear the DTCs and retest
To check the air pressure sensor, use the Jaguar Land Rover Approved Diagnostic Equipment to vent the common gallery via the exhaust valve. Then disconnect the 8mm delivery pipe from the delivery port on the back of the air dryer and connect a T-piece fitting. Connect one port of the T-piece to the blue delivery port via a short length of 8mm pipe. Connect the other port of the T-piece to a calibrated pressure gauge tool (Note that an 8mm connector will be required). Using the Jaguar Land Rover Approved Diagnostic Equipment, run the suspension air supply unit until the pressure is in the range 1500 - 1800 Kpa. Read the system pressure using the Jaguar Land Rover Approved Diagnostic Equipment. Divide the measurement in Kpa by 100 then subtract 1 at sea level (0.9 at 900m elevation, 0.8 at 1900m elevation, or 0.7 at 3000m elevation) to convert to bar and compare the result with that displayed by the pressure gauge. If the readings are not within 2.0 bar of each other, then the pressure sensor is likely to be faulty. In the case of a faulty pressure sensor, check and install a new valve block as required. Clear the DTCs and retest
To check for a stuck exhaust valve, use the Jaguar Land Rover Approved Diagnostic Equipment to run the suspension air supply unit until a gallery pressure of at least 500 Kpa is reached, then switch off the suspension air supply unit and ensure all valves are closed before opening the exhaust valve and noting any changes in gallery pressure. If the gallery pressure drops quickly to between 125 Kpa and 250 Kpa at sea level (115 Kpa and 240 Kpa at 900m elevation, 105 Kpa and 230 Kpa at 1900m elevation, or 95 Kpa and 220 Kpa at 3000m elevation) then the exhaust valve is operating correctly. If the gallery pressure cannot vent quickly below 220 Kpa to 250 Kpa (elevation dependent, see above), then there is a fault with the air suspension system or its exhaust valve. Disconnect the 8mm delivery pipe from the delivery port on the back of the air dryer. Connect a calibrated pressure gauge tool directly into the delivery port. (Note that an 8mm connector will be required). Run the suspension air supply unit to generate 3 to 4 bar and then actuate the exhaust valve. If the pressure cannot vent quickly to between 0.25 bar and 1.5 bar then the exhaust valve is the likely cause of failure. In this case, check and install a new suspension air supply unit as required. If the pressure can vent quickly to between 0.25 bar and 1.5 bar then check for a blockage in the pipe between the compressor and the rear valve block, and/or a blockage in the rear valve block, and/or a pressure sensor fault. In the case of a blocked pipe, repair or replace the faulty pipe as required. In the case of a blockage in the rear valve block or a pressure sensor fault, check and install a new rear valve block as required. Clear the DTCs and retest