The Engine Crank Inhibit (ECI) feature of the ECM is used to control the operation of the cranking motor. The ECM prevents the cranking motor from being engaged when the engine is running. The transmission neutral safety switch or clutch switch will prevent the cranking motor from being engaged when the transmission is in gear or when the clutch pedal is not depressed.
For Engine Crank Inhibit Relay with a driveline status switch Type I, see Figure
“Wiring a Crank Inhibit Relay with a Driveline Status Switch Type I”
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Figure 1. Wiring a Crank Inhibit Relay with a Driveline Status Switch Type I
For Engine Crank Inhibit Relay with a driveline status switch Type II, see Figure
“Wiring a Crank Inhibit Relay with a Driveline Status Switch Type II”
.
Figure 2. Wiring a Crank Inhibit Relay with a Driveline Status Switch Type II
For Engine Crank Inhibit Relay without a driveline status switch, see Figure
“Wiring a Crank Inhibit Relay without a Driveline Status Switch”
.
Figure 3. Wiring a Crank Inhibit Relay without a Driveline Status Switch
Section 24.1.1
ECM
The ECM prevents the engine from being cranked if the engine is already running. It does this by not allowing the ECI relay to be enabled.
Section 24.1.2
Engine Crank Inhibit Relay
The ECI relay controls the start relay. The ECI relay receives signals from the ignition switch and ECM to close the relay. Current to the relay is supplied from the neutral safety switch with automatic transmission or clutch with manual transmission.
Section 24.1.3
Start Relay
The start relay switches battery power to the crank motor solenoid when the crank inhibit relay is energized. With thermal overcrank protection, the relay is also controlled by the overcrank thermocouple.
Section 24.1.4
Clutch Switch
On vehicles equipped with manual transmissions, the clutch switch supplies switched power to the ECI relay and provides a signal to the ECM that indicates the driveline is disengaged. On vehicles programmed for manual transmissions, a 0 volt signal on the DDS circuit indicates that the clutch is disengaged (clutch pedal down); a 12 volt signal indicates that the clutch is engaged (clutch pedal up). When the clutch pedal is up, no power is available to the ECI relay.
Section 24.1.5
Neutral Switch
On vehicles equipped with mechanical automatic transmissions (Allison AT/MT), the neutral position switch supplies switched power to the ECI relay and provides a signal to the ECM that indicates the driveline is disengaged. On vehicles programmed for Allison AT/MT transmissions, a 12 volt signal on the DDS circuit indicates that the transmission is out of gear; a 0 volt signal indicates that the transmission is in gear. When the transmission is in gear, no power is available to the ECI relay.
Section 24.1.6
WTEC VIM Relay
On vehicles equipped with the electronic Allison MD WTEC transmission, the transmission controller provides a signal to a relay in the VIM module that supplies switched power to the ECI relay and provides a signal to the ECM to indicate that the driveline is disengaged.
On vehicles programmed for Allison MD transmissions, a 12 volt signal on the DDS circuit indicates that the transmission is out of gear; a 0 volt signal indicates that the transmission is in gear. When the transmission is in gear, no power is available to the ECI relay.
Section 24.1.7
Fault Detection Management
The ECM does not monitor the cranking system circuits. There are no fault codes for this system.
Before testing the ECI or cranking circuits, verify that batteries are fully charged. Check battery connections at battery, frame and starter.
Start relay voltage and resistance checks with the start relay removed are listed in Table
“Start Relay Voltage and Resistance Checks — Start Relay Removed”
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| Test Points | Specs. | Comments |
| 86 to Grd | 12v ± 1.5v | Check with relay unplugged and starter switch (key or button) engaged. If no voltage present, troubleshoot the clutch or transmission switch, the ECI circuit or ignition crank circuit. |
| 85 to Grd | < 5 Ω | An open to ground will cause the relay not to energize. (Check the thermal overcrank switch.) |
| Crank Circuit Test – With the transmission out of gear and the clutch depressed with wheels blocked, momentarily insert a jumper wire between socket pins #30 and #87 of the Start Relay.
NOTE: If the cranking circuit is functional, the engine will crank. If the engine cranks and voltage is present at #86 and ground at #85, the relay is bad. |
||
ECI relay voltage and resistance checks with the ECI relay removed are listed in Table
“ECI Relay Voltage and Resistance Checks — ECI Relay Removed”
.
| Test Points | Specs. | Comments |
| 85 to Grd | 12v ± 1.5v | Check with relay unplugged and starter switch (key or button) engaged. If no voltage present, troubleshoot ignition crank circuit. |
| 30 to Grd | 12v ± 1.5v | If no voltage present when clutch is depressed or automatic transmission in neutral, troubleshoot clutch switch or neutral switch circuit. |
| 86 to Grd | 4 to 5v | ECM will pull circuit up to 4 to 5 volts with key ON; will go to 0 volts with clutch depressed or transmission in neutral. |
| ECI Circuit Test – With the transmission out of gear, and the clutch depressed, wheels blocked, insert a jumper wire between socket pins #85 and #87 of the ECI relay. If the engine cranks when the start switch is engaged, either the ECI relay is bad or there is a problem with the ECM or ECM wiring. | ||
Section 24.1.8
Engine Crank Inhibit Description
The engine starting system is controlled by the ECM. This is to prevent cranking motor operation while the engine is running, causing damage to the starter pinion and ring gear. In series with the ECI relay is a clutch switch or transmission neutral switch. These switches prevent the cranking motor from being engaged unless the transmission is in neutral or the clutch is depressed.
Components of the system are:
- Ignition switch
- Push button start switch (optional)
- Engine Crank Inhibit (ECI) Relay
- Start relay
- Crank motor and solenoid
- Batteries and cables
- Neutral safety switch (with AT/MT automatic transmission)
- Clutch switch (with manual transmission)
- VIM relay module (with MD automatic transmission.
Section 24.1.9
System Operation
When the ignition switch is turned to the start position, with the ignition switch on and the pushbutton start switch depressed, current flows to the ECI relay. The relay is then enabled if the ECM supplies the ground circuit for the relay control windings.
Closing this relay allows current to pass from the ignition switch through the fuse, through the neutral safety switch (jumped if manual transmission), and through the clutch switch normally closed (jumped if automatic transmission). With the relay closed, current then passes through the relay and will energize the start relay. The ground circuit for the start relay is through the overcrank protection fuse in the crank motor, or directly to ground if not equipped with overcrank protection. When the relay is closed, the current can then pass from the crank motor battery terminal through the relay and to the crank motor solenoid, start terminal. This closes the crank solenoid to engage the starter.
Section 24.1.10
ECM
When the ECM recognizes that the engine is not running, the ECM will ground terminal 46. This provides the 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, the ECM will open terminal 46. This will prevent the ECI relay from closing, thus preventing the starter motor from engaging.
Section 24.1.11
Engine Crank Inhibit Relay
The ECI relay controls the current to the start relay. Turning the ignition key to the start position supplies current to energize the relay at terminal 85. If the engine is not running, the ECM terminal 46 will enable the relay by supplying a ground circuit to terminal 86 of the relay. Current for the start relay is supplied through the neutral safety switch if the transmission is in neutral with an automatic transmission to terminal 30. Or, if the vehicle is equipped with a manual transmission, current will be supplied to the relay through the clutch switch if the clutch pedal is depressed. With the relay closed, current can then pass through the relay to terminal 86 to power the start relay.
Section 24.1.12
Start Relay
The start relay switches battery power to the crank motor solenoid when the crank inhibit relay is energized. Then the ECI relay is closed, current is supplied to the start relay terminal to energize the relay. The start relay control is grounded through the starter thermal overcrank protection thermocouple, if equipped. Or, if not, the relay is grounded directly to the ground stud on the starter. With the start relay energized, battery voltage is supplied to the start relay, and then switched to the crank motor solenoid to crank the engine.
Before troubleshooting, ensure the batteries are fully charged. Check the battery cables and grounds for clean and tight connections, free of damage. Voltage readings will not be accurate if the batteries are not fully charged.
Before troubleshooting, inspect circuit connectors for pushed back, loose or damaged (spread or bent) terminals, or wires with cut strands, etc. Wires and connections must be free of damage or corrosion. When some connectors corrode, a light white residue will be present and must be removed.
Before troubleshooting, inspect the suspect circuit ground for clean, tight connections, free of any damage.
| Series 40E Troubleshooting Manual – 6SE241 |
| Generated on 10-13-2008 |