Series 40E Troubleshooting – Section 10.12 ECM Voltage

Section 10.12
ECM Voltage

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Figure 1. Diagnostic Form

Sufficient voltage and current is needed to operate the ECM. For a reproduction of the applicable portion of the diagnostic form,see Figure
“Diagnostic Form”

, above.‪

Section 10.12.1

The ECM requires 7 volts minimum to operate and drive the injectors. This is an alternate method to be used if the EST is unavailable or fails to function properly. Insufficient electrical power from the batteries or an electronic failure may inhibit the EST from receiving diagnostic data.‪

Section 10.12.2
Test Procedure

All tests must be performed with fully charged batteries.‪

Voltage Measurement at Battery

Use the following procedure to measure voltage at the battery:‪

  1. Turn all accessories off and connect a DVOM (Digital Volt Ohm Meter) across the battery terminals.
  2. Crank the engine.

Record the lowest voltage obtained during engine cranking. If the voltage is below 7 volts, the ECM power relay may be resetting due to the lack of voltage and current from the batteries, or a problem exists in the starting system.‪

If voltage is within specification, perform the voltage measurement at the ECM with a breakout box. Refer to “ Voltage Measurement at ECM With Breakout Box”


Voltage Measurement at ECM With Breakout Box

Follow these steps to measure voltage at the ECM with a breakout box:‪

  1. Remove the 60–way chassis (lower) connector harness from the ECM.
  2. Install the breakout box adaptor connectors to the chassis female connections on the ECM. Again connect the chassis harness connector to the breakout box adaptor connector. Torque the connector to ECM to 35 lb·in. See Figure
    “Breakout Box Connection”


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    Figure 2. Breakout Box Connection

  3. Connect the leads of the voltmeter to each of the three separate test points {(21+ & 1–), (22+ & 2–), (24+ & 23–)} on the breakout box.
  4. Record the lowest voltage observed at each of the test points while cranking the engine. See Figure
    “Measuring ECM Voltage with Breakout Box”


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    1. Breakout Box‪

    Figure 3. Measuring ECM Voltage with Breakout Box

  5. If voltage is lower than 7 volts, repair the ECM power feed circuit. Refer to “22.1 Circuit Functions”


Section 10.12.3
Possible Causes

Possible causes for the hard start/no start diagnosis are:‪

  • Low battery voltage
  • Bad batteries, high resistance at the battery cable connections or a defective starter
  • Low or no battery voltage to the ECM that may be due to high resistance or an open circuit in the power feed circuit to the ECM, or its power relay. The ECM power circuit fuse located in the battery box may be open or the ECM power relay may be defective.

Section 10.12.4
Tools Required

DVOM and breakout Box, J 43102‪

Section 10.12.5
Supplemental Diagnostics

Refer to “22.1 Circuit Functions”

, for power circuit diagnostics.‪

Series 40E Troubleshooting Manual – 6SE241
Generated on 10-13-2008