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| Illustration 1 | g01253937 |
Schematic of the bypass pressure switch for the transmission oil filter | |
This diagnostic trouble code is associated with the bypass pressure switch for the transmission oil filter. The FMI 3 means that the ECU has detected the voltage as being above normal when the engine is not running. The code will change to an FMI16 when the engine is running. The bypass switch is a normally open switch. The switch will become closed when the switch is installed. The switch will then become open when the filter is plugged and the oil needs to bypass the filter in order for the transmission to receive oil.
Note: In this application, a transmission a "High Oil Temperature Lamp" may be enabled when this diagnostic code is active.
The possible causes of this diagnostic trouble code are listed:
- Short to the + battery terminal.
- The circuit is open.
- A failed switch
- The ECU may have failed. The ECU failing is unlikely.
Note: The following test procedure may create other diagnostic trouble codes. Ignore these created diagnostic trouble codes and clear these diagnostic trouble codes when the original diagnostic trouble code has been corrected. Ensure that the diagnostic trouble code of SPN 126 FMI 3 is active before performing this procedure.
Note: Use a digital multimeter for the measurements in this procedure.
Test Step 1. CHECK FOR AN OPEN CIRCUIT.
- Turn the disconnect switch and the key start switch to the ON position.
- Disconnect the harness from the switch.
- Connect a jumper wire to pin 1 and pin 2 of the harness.
- Observe the status of the diagnostic trouble code.
Expected Result:
The diagnostic trouble code of SPN 126 FMI 3 is still active.
Results:
- YES - The diagnostic trouble code is still active. Proceed to 2.
- NO - The diagnostic trouble code is no longer active. Proceed to 3.
Test Step 2. CHECK FOR A SHORT CIRCUIT TO POSITIVE VOLTAGE.
- The disconnect switch remains in the OFF position.
- Disconnect the harness from the ECU.
- At the J1 machine harness connector, measure the resistance from contact J1-63 and contact J1-21 to all other J1 and J2 contacts and to all possible sources of positive voltage.
Expected Result:
The resistance measurement is greater than 5000 ohms for each measurement.
Results:
- OK - The resistance measurement is greater than 5000 ohms for each measurement. The circuit is correct. Proceed to Test Step 4.
- NOT OK - The resistance measurement is not greater than 5000 ohms for one or more measurements. A short exists in the circuit.
Repair: The short is in the circuit with the low resistance measurement. Repair the harness or replace the harness. Verify that the problem has been corrected.
STOP
Test Step 3. CHECK THE SWITCH FOR PROPER OPERATION.
- Disconnect the switch and remove the switch from the vehicle.
- Replace the switch with a new switch.
- Observe the status of the diagnostic trouble code.
Expected Result:
The switch is operating correctly and the diagnostic trouble code is not active.
Results:
- YES - The diagnostic trouble code is not active. The new switch has corrected the problem. The original switch was faulty.STOP
- NO - The diagnostic trouble code is active. The new switch has not corrected the problem. Proceed to Test Step 4.
Test Step 4. CHECK IF THE DIAGNOSTIC TROUBLE CODE IS STILL ACTIVE.
- Inspect the harness connectors. Clean the contacts of the harness connectors and check the wires for damage to the insulation that is caused by excessive heat, battery acid, or chafing.
- Perform a 45 N (10 lb) pull test on each of the wires that are associated with the circuit.
- Reconnect all harness connectors. Make sure that the harness connectors are fully seated and that the clips for each connector are completely fastened.
- Turn the disconnect switch and the key start switch to the ON position.
- Operate the vehicle.
- Determine if the SPN 126 FMI 3 is active.
Expected Result:
The SPN 126 FMI 3 is active.
Results:
- YES - The SPN 126 FMI 3 is active. The diagnostic trouble code has not been corrected.
Repair: Check the circuit again. It is unlikely that the ECU has failed. Exit this procedure and perform this procedure again. If the cause of the diagnostic trouble code is not found, replace the ECU. Prior to replacing an ECU, always contact your dealership for possible consultation with Caterpillar. This consultation may greatly reduce repair time. See Testing and Adjusting, "Electronic Control Unit - Replace".
STOP
- NO - The SPN 126 FMI 3 is not active. The diagnostic trouble code does not exist at this time. The initial diagnostic trouble code was probably caused by a poor electrical connection at one of the harness connectors that was disconnected and reconnected. Resume normal vehicle operation.STOP