Series 40E Troubleshooting – Section 22.1 Circuit Functions


Section 22.1
Circuit Functions

The ECM requires a 12 volt source of power to perform its functions. It receives this operating power directly from the vehicle batteries via the ECM relay contacts each time the ignition key switch is turned to the on position. Turning the ignition key switch ON causes the ECM to provide an internal ground to the coil side of the ECM relay. This causes the relay to close its contacts and provide the ECM with the power necessary to perform its various functions. For ECM Power Supply Diagram, see Figure
“ECM Power Supply Diagram”

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Figure 1. ECM Power Supply Diagram

Section 22.1.1
Fault Detection Management

The ECM internally monitors battery voltage. If the ECM continuously receives less than 6.5 volts or more than 18 volts, a fault code will be set. The fault code will not cause the warning light to turn ON. If the condition is intermittent, the code will be logged as an inactive code. The ECM will not operate at voltages continuously below 6.5 or above 18 volts. See Figure
“Main Power Relay Wiring”

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Figure 2. Main Power Relay Wiring

Perform the following checks with the ECM relay removed and the ignition key ON, engine OFF. Voltage checks at the ECM Power Relay Socket are listed in Table
“Key ON Engine OFF — Voltage Checks at ECM Power Relay Socket”

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+Test Points‪

Spec‪

Comments‪

85 to Grd‪

12v ± 1.5v‪

Voltage present at all times. If no voltage, check ground and power circuits from chassis connectors.‪

30 to Grd‪

12v ± 1.5v‪

Voltage present at all times. If no voltage, check ground and power circuits to battery circuits.‪

86 to Grd‪

0.6 to 2v‪

ECM grounds relay through internal transistor. Expect 1.2v with key ON relay removed.‪

87 to Grd‪

0v‪

No voltage present when relay is removed.‪

Table 1. Key ON Engine OFF — Voltage Checks at ECM Power Relay Socket

The following checks are to be made with the breakout box installed, the ECM power relay installed, and the ignition key ON. Voltage checks at the ECM are listed in Table
“Key ON Engine OFF — Voltage Checks at ECM”

. ‪

+Test Points‪

Spec‪

Comments‪

21 to Grd‪

12v ± 1.5v‪

Power from relay to ECM.‪

22 to Grd‪

12v ± 1.5v‪

Power from relay to ECM.‪

41 to Grd‪

12v ± 1.5v‪

Power from relay to ECM.‪

25 to Grd‪

0.6 to 2v‪

ECM grounds relay through internal transistor. Expect 1.2v with key ON.‪

Table 2. Key ON Engine OFF — Voltage Checks at ECM

Circuit resistance checks are made with the breakout box installed, the ECM power relay installed and the ignition key OFF. These checks are listed in Table
“Circuit Resistance Checks”

. ‪

+Test Points‪

Spec.‪

Comments‪

240 to 25‪

60-120 Ω‪

Measure resistance across the relay coil; remove fuse 240 to test.‪

30 to 564A‪

< 5 Ω‪

Power from the relay to the ECM (Remove relay to test, and test at location 30 in relay socket.)‪

Table 3. Circuit Resistance Checks

Fault code descriptions are listed in Table
“Fault Code Descriptions”

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Fault Code‪

Descriptions‪

112‪

Internal ECM voltage was detected above 18 volts.‪

113‪

Internal ECM voltage was detected below 6.5 volts.‪

626‪

ECM detected intermittent power loss through the ECM relay.‪

Table 4. Fault Code Descriptions

Section 22.1.2
Description

The ECM receives its power directly from the vehicle batteries when the ECM power relay is energized. This allows maximum power transfer from the batteries to the ECM with a minimum amount of power loss. The wire harness that supplies ECM power is fused at the battery to protect it from short circuits.‪

When the key switch is turned ON, ignition power from the fuse is supplied to the cavity of the ECM through the connector. This indicates to the ECM that the ignition switch is ON, and it is time to enable the ECM power relay.‪

Power to the ECM power relay control coil (terminal 85) is provided by circuit 564B from the battery feed stud through the 31–pin connector. The ECM will enable the ECM power relay by completing the ground circuit (internally) to the relay at ECM pin 25.‪

When the ECM power relay is enabled, power at terminal 30 from the vehicle batteries is switched directly to the ECM from terminal 87 of the relay to pins 21, 22 and 41 of the ECM. The vehicle battery power for this relay to switch is supplied directly from the battery to terminal 30 of the relay. ‪

Section 22.1.3
ECM Diagnostics

If the ECM detects more than 18 volts at pins 21, 22 and 41, it will set Flash Code 112. A voltage of less than 6.5 volts detected by the ECM will set Flash Code 113. The ECM is capable of detecting an intermittent interruption of power or ground circuits. Flash Code 626 will be set indicating an unexpected reset has occurred.‪

Section 22.1.4
Flash Codes

The following ECM Power Supply faults can occur:‪

Section 22.1.4.1
Flash Code 112

ATA Code PID 168 FMI 35‪

ECM: Internal voltage power out of range HIGH.‪

Flash Code 112 can be caused by: ‪

  • Defective alternator causing an alternator output voltage in excess of 18 volts.
  • Additional voltage provided while attempting to jump start engine or improper external battery connections that could cause the additional voltage increase.

If the condition causing Flash Code 112 is intermittent, the code will change from active to inactive status. Code 112 does not cause the Engine Warning Light to turn ON.‪

Section 22.1.4.2
Flash Code 113

ATA Code PID 168 FMI 36‪

ECM: Internal voltage power out of range LOW.‪

Code 113 can be caused by consistently less than 6.5 volts being applied to ECM pins 21, 22 and 41. This can be caused by a defective alternator or ECM power relay, discharged batteries, and/or increased resistance in the battery feed circuits. Code 113 does not turn the Engine Warning Light ON. If the condition causing Code 113 to set is an intermittent condition, when the condition is no longer present, the code status will change from active to inactive.‪

Section 22.1.4.3
Flash Code 626

ATA Code PID 254 FMI 56‪

ECM: Unexpected reset fault.‪

Any time power is interrupted to the ECM due to intermittent power feed circuits caused by loose or dirty connections at the batteries or at ground cables, the ECM may power down. When the power or ground circuit becomes intact again, the ECM will reboot itself. This may cause erratic engine operation. Flash Code 626 will be set anytime the flow of power is interrupted to the ECM. Turning the ignition key OFF and then ON again causes the code to change from an active to an inactive code status. Code 626 will not cause the Engine Warning Light to illuminate.‪

Section 22.1.5
Before Performing Tests

Inspect the ECM power relay circuit connectors for pushed back, damaged, corroded or dirty terminals as well as ensuring the terminals and wires are properly crimped. Ensure connectors are properly joined together. Also, check for damage to wiring, and check for clean, tight battery and ground connections.‪

Section 22.1.6
Troubleshooting

If Flash Code 626 is active, the voltage at pins 21, 22 and 41 of the ECM should be monitored while looking for an intermittent connection in the power feed wiring. The EST may be used to indicate any fault codes as well as displaying the voltage as measured by the ECM.‪


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