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TM 5-4210-233-14&P-1
Table 4-2. Unit Troubleshooting - Continued
MALFUNCTION
TEST OR INSPECTION
CORRECTIVE ACTION
ELECTRICAL SYSTEM - JACOBS ENGINE BRAKE
1
JACOBS ENGINE BRAKE DOES NOT ACTIVATE WITH CAB SWITCH
(Refer to Electrical Wiring Diagrams, Appendix H, Sheet 14 of 16.)
Step 1.
Check that pump shift switch is in ROAD position.
Shift pump to ROAD position.
Step 2.
Check switch for proper operation.
Replace switch (see para 4-9.4).
Step 3.
Condition of truck is not correct for Jacobs brake operation, torque converter must be
locked up, throttle off.
Lock up torque converter, place throttle off.
Step 4.
Check wire D508 is ground for and for continuity to DDEC.
Replace wire (see para 4-9.4).
Step 5.
Check torque converter lockup psi switch for proper operation. (Continuity between wires
1093 and 1162 when torque converter is locked).
Replace switch (see para 4-9.4).
Step 6.
With wire 1657 disconnected from pump in gear auto disengage relay, check for
+12V at wire 1099.
Replace auto disengage relay (see para 4-9.4).
Step 7.
With wire D508 removed and throttle control relay terminal 85 connected to ground,
check for +12Von wire 1093L.
Replace throttle control (disenable) relay (see para 4-9.4).
Step 8.
Check for +12V at wire 1161 at circuit breaker.
Replace breaker (see para 4-99).
Step 8.
Check wiring for continuity.
Replace wire (see para 4-9.4).
4-107
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