Navistar N9 Diagnostic Manual page 49

1 DIAGNOSTIC TROUBLESHOOTING PROCEDURES
Step
Determine if vehicle has an anti-theft system installed.
6
Look for anti-theft password switch panel on vehicle center panel.
Does vehicle have an anti-theft system installed?
Step
Determine if ECM MPR ground circuit is operating properly.
7
A. Key-On Engine-Off (KOEO)
B. Remove ECM PWR Relay
C. Measure voltage between battery positive and ECM PWR relay pin-85
Is voltage between pin 85 and battery positive within 0.5V of battery voltage?
Step
Determine if ECM MPR ground circuit is open
8
A. Key-On Engine-Off (KOEO)
B. Measure voltage between battery positive and pin C-70
Is voltage between pin C-70 and battery positive within 0.5V of battery voltage?
Step
Determine if Engine Control Module (ECM) is operating properly.
9
A. Install a known good test ECM
B. Attempt to recreate original problem
Does original problem occur with test ECM?
Decision
Yes: See Electrical System
troubleshooting Guide for Anti-Theft
System checks. After repairs
are complete, retest for original
problem.
No: Repair SWBAT ignition switch
circuit. After repairs are complete,
retest for original problem.
Decision
Yes: Go to Step 10
No: Go to Step 8
Decision
Yes: Go to Step 10
No: Go to Step 9
Decision
Yes: Install original ECM. Verify
each step was completed correctly
and the proper decision was made.
No: Replace ECM. After repairs
are complete, retest for original
problem.
45