11. Main Power Relay To Ecm; Voltage Measurement With Breakout Harness At Main Power Relay - Navistar International DT 466 Diagnostic/Troubleshooting Manual

174

11. Main Power Relay to ECM

Figure 203
Purpose
To determine correct power supplied to operate the
ECM
The ECM requires 7 V minimum for correct operation.
Voltage Measurement with Breakout Harness at
Main Power Relay
Tools
• Relay Breakout Harness
• DMM
Procedure
WARNING: To avoid serious personal injury,
possible death, or damage to the engine or
vehicle, read all safety instructions in the "Safety
Information" section of this manual.
NOTE: Batteries must be fully charged before doing
the following steps.
1. Turn the ignition switch to OFF and ensure all
accessories are turned off.
Read all safety instructions in the "Safety Information" section of this manual before doing any procedures.
5 HARD START AND NO START DIAGNOSTICS
Follow all warnings, cautions, and notes.
© August 2008 Navistar, Inc.
Figure 204 Relay Breakout Harness to power
distribution center
2. Connect Relay Breakout Harness between ECM
main power relay and power distribution center or
chassis harness depending on application.
NOTE: Depending on application, the relay could
be one of two kinds. Check power distribution
center or cab cowl.
3. Connect DMM POS to lead 87 and NEG to ground
terminal on cowl.
4. Crank engine for 20 seconds and measure
voltage.
5. Record the lowest voltage on Diagnostic Form.
• If the voltage is below 7 V, the ECM main
power relay may be resetting, due to low
voltage and current from the batteries, or
problems in the ignition circuit and power
feed circuits. See Electronic Control Module
Power (ECM PWR) in Section 7 (page 381).
• If the voltage is above 7 V, continue with Hard
Start and No Start Diagnostic tests.
NOTE: Results can be above 7 V, but there
may be a problem between the main power
relay and the ECM. If a Hard Start / No Start
problem remains after all Diagnostic Form tests
are complete, do Voltage Measurement at ECM
with Breakout Box.
EGES-270-1