ELECTRICAL SYSTEM TESTS, INSPECTIONS, AND ADJUSTMENTS - CONTINUED
ELECTRICAL POWER SUPPLY CIRCUIT TEST
N OT E
Use this test to troubleshoot anysuspected problems with power to ECM.
This procedure covers folowing diagnostic codes:
a. 168-00 "System Voltage High"
b. 168-01 "System Voltage Low"
c. 168-02 "System Voltage Intermittent/Erratic"
Use this test if there are intermittent engine shudowns or if a difficulty in starting is not accompa-
nied by loss of electrical accessories. Engine shutdowns accompanied by a loss of other electrical
accessories indicates problem in engine start switch.
This does not indicate a problem in wiring atengine's ECM. Verify there are no problems with
starting system or charging system before you use this test.
Unswitched battery voltage is supplied to ECM atP1-48, P1-52, and P1-53. Negative battery is
supplied to ECM at P1-61, P1-63, and P1-65.
ECM receives input from engine start switch at P1-70 when engine star switch is in ON or
When ECM detects battery voltageat this input, ECM will power up. When battery voltage is
removed from this input, ECM will power down.
ECM continuously receives battery voltage throug unswitched cab buss circuit breaker and fuse
for engine ECM.
Engine ECM requires engine start switch to be inON position to maintain communications with