Conditions Which Generate This Code:
Connections of the parking brake switch
The CID 0070 diagnostic code is associated with the parking brake switch. The FMI 04 diagnostic code is activated when both of the inputs are showing a ground signal at the same time.
The parking brake switch is a two pole double throw switch. One pole is used to provide two switch to ground inputs to the Power Train ECM in order to indicate the status of the switch. The other switch pole is used to energize the parking brake dump solenoid. During normal operation, one of the inputs is not connected to ground and the other input is connected to ground through the switch contacts. An internal pull-up voltage is present at the ECM switch inputs. When the input is grounded through the switch, the ECM detects the ground signal. When the brake is applied, system voltage is directed to the parking brake solenoid through Fuse 20. This results in the parking brake being engaged. The ECM will determine that the switch is in the brake ON position when the input at J1-35 is grounded.
The possible causes of this diagnostic code are listed:
- The switch has failed.
- There is a short to a ground in one or both of the input circuits.
- The ECM has failed. An ECM failure is unlikely.
|Parking brake switch contact states|
|Switch Position||J1-35 wire( 419-YL)||J1-40 wire (F780-PK)|
|Brake ON||Closed (1)||Open (2)|
|Brake OFF||Open (2)||Closed (1)|
|( 1 )||Closed to ground wire (L740-BR)|
|( 2 )||Open to ground wire (L740-BR)|
Note: Before performing this procedure, inspect the harness connectors that are involved in the circuit. Poor connections can often be the cause of a problem in an electrical circuit. Verify that all connections in the circuit are clean, that all connections are secure and that all connections are in good condition. If a problem with a connection is found, correct the problem and verify that this diagnostic code is active before performing this procedure.
Note: The following test procedure may create other diagnostic codes. Ignore these created diagnostic codes and clear these diagnostic codes when the original diagnostic code has been corrected. Ensure that the diagnostic code of CID 0070 – FMI 04 is active before performing this procedure.
Note: Use a digital multimeter for the measurements in this procedure.
Test Step 1. CHECK THE OPERATION OF THE SWITCH
- Turn the key start switch and the disconnect switch to the OFF position.
- Disconnect the machine harness connector from the switch.
- Turn the disconnect switch and the key start switch to the ON position. Do not start the engine.
- Observe the status of the FMI 04 diagnostic code.
An FMI 03 diagnostic code has not been activated by the ECM. The FMI 04 diagnostic code remains active when the switch is disconnected.
- YES – The FMI 04 diagnostic code remains active when the harness connector is disconnected. The switch is not causing the problem. Proceed to Test Step 2.
- NO – The FMI 04 diagnostic code is no longer active. An FMI 03 diagnostic code has been activated by the ECM.
Repair: The switch has failed. Replace the switch. Verify that the new switch has corrected the problem before operating the machine.
Test Step 2. CHECK THE INPUT CIRCUITS FOR A SHORT
The machine harness remains disconnected from the switch.
- Turn the disconnect switch and the key start switch to the OFF position.
- Disconnect the J1 and J2 machine harness connectors from the ECM.
- At the J1 machine harness connector for the ECM, measure the resistance between contact J1-35 wire (419-YL) and a clean source of frame ground. Measure the resistance between contact J1-35 wire (419-YL) and all of the other contacts that are used in the machine harness connectors for the ECM.
- At the J1 machine harness connector for the ECM, measure the resistance between contact J1-40 wire (F780-PK) and a clean source of frame ground. Measure the resistance between contact J1-40 wire (F780-PK) and all of the other contacts that are used in the machine harness connectors for the ECM.
Each resistance measurement is greater than 5000 ohms.
- YES – Each resistance measurement is greater than 5000 ohms. The machine harness is correct. Proceed to Test Step 3.
- NO – One or more of the resistance measurements is less than 5000 ohms. There is a short circuit in the machine harness.
Repair: There is a short circuit in the machine harness. The problem is between the wires with the low resistance measurements. Refer to Electrical System Schematic, KENR8916. Examine all of the connectors that are in the circuit. Ensure that the connections are clean and secure. Repair the machine harness or replace the machine harness.
Test Step 3. CHECK THE STATUS OF THE DIAGNOSTIC CODE
- Inspect the contacts of the harness connectors and clean the harness connectors.
- Reconnect all harness connectors.
- Turn the disconnect switch and the key start switch to the ON position.
- Operate the machine.
- Check the status of the CID 0070 FMI 04 diagnostic code.
The CID 0070 FMI 04 diagnostic code is not active.
- YES – The CID 0070 FMI 04 diagnostic code is not active. The diagnostic code does not exist at this time. The initial diagnostic code may have been caused by a poor electrical connection that was corrected when a harness connector was disconnected and reconnected.
Repair: Resume normal operation.
- NO – The CID 0070 FMI 04 diagnostic code is active. The problem has not been corrected.
Repair: With Caterpillar Electronic Technician (Cat ET), if available, perform a “Wiggle Test” on the parking brake switch circuit in the machine wiring harness. The wiggle test may detect momentary or intermittent shorts or opens in the machine wiring harness.If all possible causes of the problem have been investigated and no problem can be found, you may need to replace the Power Train ECM.Prior to replacing an ECM, always contact the Technical Communicator at your dealership for possible consultation with Caterpillar. This consultation may greatly reduce repair time and expense. If the ECM must be replaced, refer to Testing and Adjusting, “Electronic Control Module (ECM) – Replace”.