Purpose
To determine correct power supplied to operate the IDM
The IDM requires 7 V minimum for correct operation.
Voltage Measurement at 12–Pin Connection with Breakout Harness
Tools
• 12-Pin Breakout Harness
• Digital Multimeter (DMM)
Procedure
NOTE: Batteries must be fully charged before doing the following steps.
1. Turn the ignition switch to OFF and ensure all accessories turned off.
2. Disconnect 12-pin connector above the ECM and IDM.
CAUTION: When disconnecting the 12-pin connector, the lock can come loose. Put the lock back in the
correct place before reconnecting the connector.
3. Connect 12-pin Breakout Harness between both engine and chassis connectors.
4. Connect leads of the DMM to each of the following test points:
• POS 12 to NEG 1 (IDM PWR to IDM GND)
• POS 9 to NEG 1 (VIGN to IDM GND)
• POS 9 to NEG 8 (VIGN to MPR)
• POS 6 to NEG 1 (IDM Logic PWR to IDM GND)
5. Crank engine for 20 seconds and measure voltage.
6. Record the lowest voltage on Diagnostic Form.
• If the voltage is below 7 V, the IDM main power relay may be resetting, resulting from low voltage and current from the batteries or problems in the ignition circuit or power feed circuits. See “IDM PWR, Injector Drive Module Power” (page 479) in Section 7.
• 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 12-pin connector and the IDM. If a Hard Start / No Start problem remains after all Diagnostic Form tests are complete, check voltage at IDM connector.
Possible Causes
Low battery voltage
• Failed batteries
• High-resistance at battery cable connections
• Wiring to the IDM
Low or no battery voltage to the IDM main power relay
• High-resistance or an open power feed circuit to the IDM or IDM main power relay.
• The IDM power circuit fuse in battery box may be open.
• IDM main power relay may have failed.
• VIGN circuit problem
• Failed IDM
Voltage Measurement with Breakout Harness at Main Power Relay
NOTE: This is an alternate procedure for any of the following:
• A 12-pin Breakout Harness is not available
• Expected voltages were not to spec, when using the 12-pin Breakout Harness
Tools
• Relay Breakout Harness
• Digital Multimeter (DMM)
Procedure
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.
2. Connect Relay Breakout Harness between IDM 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 lead to 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 IDM main power relay may be resetting, resulting from low voltage and current from the batteries or problems in the ignition circuit or power feed circuits. See “IDM PWR, Injector Drive Module Power” in Section 7 (page 479).
• If the voltage is above 7 V, continue with Hard Start and No Start tests.
NOTE: Results can be above 7 V, but there may be a problem between the main power relay and IDM. If a Hard Start / No Start problem remains after all Diagnostic Form tests are complete, check voltage at 12-pin connector and IDM
connector.