The function diagram for the ECI system consists of the following.
• Electronic Control Module (ECM)
• Starter
• Starter relay
• World Transmission Electronically Controlled (WTEC)
• Neutral Start Backup Switch (NSBU)
• Driveline Disengagement Switch (DDS)
Function
The Engine Crank Inhibit (ECI) is a function of the ECM to control the operation of the starter. The ECM
prevents engagement of the starter when the engine is running. This prevents damage to the starter pinion
and ring gear. The transmission neutral safety switch or clutch switch prevents engagement of the starter when the transmission is in gear or when the clutch pedal is not depressed.
The engine starter relay controls battery voltage to the starter solenoid. The starter relay can also be controlled by an optional over crank thermocouple.
Operation
The ECM controls the starting system. The clutch switch or transmission neutral switch provide input to the ECM. Both switches prevent the starter from being engaged unless the transmission is in neutral or the clutch is depressed.
Start Relay
The engine starter relay controls voltage to the starter motor. Turning the ignition switch to start position supplies current to energize the relay at Pin 86. If the engine is not running and the driveline is not engaged, the ECM Pin X3–23 will enable the relay by suppling a ground circuit to Pin 85 of the relay. When the relay is closed, current passes through the relay to the pins on the starter solenoid.
Before troubleshooting, inspect circuit connectors for loose or damaged pins or wires. Wires and connections must be free of damage or corrosion.
When connectors corrode, a white residue will be present and must be removed. Make sure the batteries are fully charged. To ensure accurate readings, check battery cables and grounds for clean and tight connections.
Clutch Switch
Manual transmissions use the clutch switch to supply a signal to the ECM indicating that the driveline
is disengaged. A 12 V signal on the Driveline Disengagement Switch (DDS) circuit indicates that the clutch is disengaged. A 0 V signal indicates that the clutch is engaged.
Neutral Switch
Allison LCT transmissions use the neutral position switch to supply power to the starter relay and a signal
to the ECM that the driveline is disengaged. Vehicles programmed for Allison AT/MT transmissions receive
a 12 V signal on the DDS circuit indicating that the transmission is out of gear. A 0 V signal indicates that
the transmission is in gear. When the transmission is in gear no power is available to the ECI relay.
WTEC MD with Auto Neutral
Allison MD World Transmission Electronically Controlled (WTEC) transmissions (with optional Auto Neutral) have a crank inhibit system with an additional relay. The relay inhibits cranking when the transmission is in auto neutral. Pin 6 of the transmission ECU controls 12 V to Pin 86 of the starter relay. Pin X3–8 of the ECM receives 12 V from
the WTEC Auto Neutral relay when the transmission is shifted to neutral or auto neutral. Without the additional relay, the DDS input (Pin X3–8) allows cranking in auto neutral.
Electronic Control Module (ECM)
When the ECM recognizes that the engine is not running and the driveline is not engaged, the ECM will ground Pin X3–23. This provides a current path for the ECI relay to close when the Start switch is engaged or the starter button is depressed.
When the ECM recognizes that the engine is running or the driveline is engaged, the ECM will open Pin
X3–23. This prevents the ECI relay from closing and the starter motor from engaging.
Fault Detection / Management
When the on demand Engine ON standard test is run, an open or short to ground can be detected on the coil side of the ECI relay.
Tools
• EST with MasterDiagnostics® software
• EZ-Tech® interface cable
• Digital Multimeter (DMM)
• Breakout Box
• 3-Banana Plug Harness
• 500 Ohm Resistor Harness
• Relay breakout harness
