TM 9-2330-294-14
Table 3-3. Troubleshooting Air SystemContinued
MALFUNCTION
TEST OR INSPECTION
CORRECTIVE ACTION
8. NO BRAKES WILL RELEASE (SEMITRAILER COUPLED TO TOWING VEHICLE)
Step 1. Check semitrailer pressure at auxiliary air supply valve using tire gage, 90-120 psi required.
If below 90 psi, replenish air supply (para 2-4).
Step 2. Check to see if intervehicular emergency air hose is improperly connected.
Shut off towing vehicle shutoff air cock. Disconnect and reconnect air hose. Open shutoff
air cock.
Step 3. Check to see if emergency air hose shutoff valve is closed (M746 only).
Open shutoff valve.
Step 4. Check to see if parking brake on towing vehicle is in applied position.
Release parking brake.
9. SERVICE BRAKE RELEASE SYSTEM INOPERATIVE
Check air pressure at auxiliary air supply valve using pressure gage. 65 psi pressure
required to hold off fail-safe power spring; 45 psi required to automatically release service
brakes.
Activate fail-safe brake release system (para 2-3).
10. FAIL-SAFE BRAKE MANUAL RELEASE SYSTEM INOPERATIVE.
Test pressure at air tank fill using tire pressure gage. 65 psi pressure required to hold
off fail-safe power spring.
Pressurize fail-safe release tank through fill fitting and manually compress fail-safe
units or pressurize entire air system (para 2-4).
SUSPENSION AIR SYSTEM
11. AIR SPRINGS AND AIR AXLE LIFTS FAIL TO INFLATE
Step 1. Check semitrailer pressure at tank valve on auxiliary air supply valve for required 90-120
psi.
Wait for brake air system to fully charge.
Step 2. Check to see if all suspension shutoff valves are closed.
Open valves (para 2-7).
TO INFLATE WHILE AIR AXLE LIFTS INFLATE
12. AIR
SPRINGS FAIL
PROPERLY.
Check to see if all the suspension shutoff valves to air springs are closed.
Open valves (para 2-7).
13. ONE SET OF AIR SPRINGS FAIL TO INFLATE
Check to see if the shutoff valve for malfunctioning air spring is closed.
Open valve (para 2-7).
14. BOTH AIR AXLE LIFTS FAIL TO INFLATE
Check to see if the shutoff valve to air springs is closed.
Open valve (para 2-7).
15. AIR SPRINGS INFLATE NORMALLY IN ONE POSITION OF AIR CONTROL
HANDLE BUT NOT IN OTHER TWO POSITIONS.
Step 1. Check vent ports in air control valve for mud, ice, or other obstructions.
Clean ports.
Step 2. Check to see if suspension shutoff valve is closed while air springs are inflated.
Open shutoff valve (para 2-7).
Section IV. MAINTENANCE PROCEDURES
NOTE
If lamp replacement does not remedy
Operator's maintenance of the electrical system
malfunction, notify organizational main-
consists of replacing defective lamps. Refer to
tenance personnel.
paragraphs 4-19c, 4-21d, 4-22a, and 4-27a f o r
replacement procedures.
