Air and oil pressure gauge failure

If pressure gauges do not show a reading, or the reading is suspected of being in error, a cluster gauge reading and master shop gauge reading should be taken by placing a Y or T connector in the circuit. If air pressure is evident at either of the two air lines, check the air filter inside the air pressure gauge to make sure it is not plugged. If the filter is not plugged, and the cluster air gauge pressure reading exceeds a 65 psi (450 kPa) master gauge reading, replace the cluster air gauge.

Recommended reading: howo A7