The service brake circuit function is to signal the ECM when the brakes are applied. This information is used to disengage the cruise control and PTO functions. The signal is also used for ECM control of the Vehicle Retarder and exhaust brake enabling. The brake signal will interrupt the Cold Ambient Protection feature and will reset the time interval for the Idle Shutdown feature. See Figure
“Service Brake Circuit Function”
.
Figure 1. Service Brake Circuit Function
Section 18.1.1
Service Brake Switches
The service brake switches send a 12 volt signal to the ECM when the brakes are applied. Both signals are normally open.
Section 18.1.2
Fault Detection Management
The ECM continuously monitors terminals 43 and 44 for voltage. Should there be a voltage at one of the terminals and not at the other, the ECM will set a fault code.
When Flash Code 222 is active, all features using brake signal inputs will be disabled.
This code will not cause the Warn Engine Light to illuminate. See Figure
“Circuit 523 and 543 Wiring Recommendation (Brake Switches)”
.
Figure 2. Circuit 523 and 543 Wiring Recommendation (Brake Switches)
Connector voltage checks are listed in Table
“Connector Voltage Checks”
.
| Test Points | Specification | Comments |
| 439G to Grd | 12v ± 1.5v | Open fuse F9 or open circuit 70 (Hydraulic and Air) |
| 439C to Grd | 12v ± 1.5v | Open fuse F33 or open circuit 90C (Hydraulic brake only) |
| 523 to Grd | 0 | Circuit 523 shorted to another circuit |
| 543 to Grd | 0 | Circuit 543 shorted to another circuit or …with hydraulic brakes shorted diode assembly or defective brake module…with air brakes defective brake relay. |
ECM connector checks with the breakout box installed, ignition switch ON and the brakes not depressed, are listed in Table
“ECM Connector Check”
.
| Test Points | Specification | Comments |
| 43+ to 42− | 0 | Circuit 423 shorted to another circuit or (with hydraulic brakes) defective brake module |
| 44+ to 42− | 0 | Circuit 543 shorted to another circuit or (with hydraulic brakes) defective brake module or shorted diode assembly. |
| Apply brakes (with air brakes, ensure sufficient air pressure is available) | ||
| 43+ to 42− | 12v ± 1.5v | If the brake switch connector test is within spec, then possible open ckt 523 or defective brake switch |
| 44+ to 42− | 12v ± 1.5v | If the brake switch connector test is within spec, then possible open ckt 543 or defective brake switch |
Fault code descriptions are listed in Table
“Fault Codes”
.
| Fault Code | Description |
| 222 | Brake switch circuit fault |
| Indicates ECM has detected that voltage at terminal 43 is not equal to voltage at terminal 44 |
Section 18.1.3
Extended Description
The service brake circuit function is to signal the ECM when the brake pedal is applied. This information is used to disengage the cruise control and PTO functions. This signal is also used for ECM control of the Vehicle Retarder and compression brake enabling. The brake signal will interrupt the Cold Ambient Protection feature and will reset the time interval for the Idle Shutdown feature.
Four systems are used for the service brake signal.
Section 18.1.4
Hydraulic Brakes
With hydraulic brakes a double pole single throw switch is used. The switch is a self adjusting switch mounted at the brake pedal. When the brake is not applied, the brake pedal holds the switch in the open state. Current is supplied by fuse to the primary side of the switch and by fuse to the secondary side of the switch. Applying the brakes closes the switch to supply current to circuits 543 and 523.
Circuit 523 supplies voltage to:
- Operate the turn signal switch relay for brake light operation.
- Circuit 523 to signal the ECM at terminal 43 to indicate the brakes have been applied.
Circuit 543 supplies voltage to the brake module and to the ECM at terminal 44 as a redundant signal to verify brake application.
Section 18.1.5
Service Brake Switch(s)
The following apply to the service brake switch:
- With tractor air brakes, a single normally open switch is used. Air pressure closes the switch with the brakes applied.
- With air brakes, two normally open air-operated switches are in parallel circuits.
- With hydraulic brakes, two mechanical switches are used, but only one of the switches is linked to the ECM. The switches are activated by the brake pedal arm.
Section 18.1.6
Flash Code
Flash Code 222
SID 247 FMI 2
ECM: Brake Switch Circuit Fault
The ECM continuously monitors terminals 43 and 44 for voltage. Should there be voltage present at one of the terminals and not at the other, the fault detection will set a fault code.
When flash code 222 is active, all features using brake signal inputs will be disabled. This code will not cause the Warn Engine Light to illuminate.
Section 18.1.6.1
Possible Causes
If an open circuit exists due to a defective fuse, switch or an open wire, voltage may not be present at either terminal 43 or 44. This would cause the fault code to be set.
Section 18.1.7
Before Troubleshooting
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.
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.
Inspect the suspect circuit ground for clean, tight connections free of damage.
Section 18.1.8
Troubleshooting
The EST service tool can be used to retrieve a fault code that has been set in the ECM. The EST may also be used to clear these fault codes once the problem has been resolved.
To determine the operation of the brake switch circuit it is possible to monitor the EST data list and the brake status will be displayed.
| Series 40E Troubleshooting Manual – 6SE241 |
| Generated on 10-13-2008 |