The Electronic Control Module (ECM) supplies a regulated voltage of 8.0 ± 0.4 VDC to the following sensors:
- Engine coolant level
- Auxiliary temperature
These sensors are optional equipment.
+8 VDC is routed from the ECM to terminal A of each digital sensor connector.
Use this procedure to troubleshoot the following diagnostic codes:
- 263-03 Digital Sensor Supply short to +batt
- 263-04 Digital Sensor Supply short to ground
A +8 V diagnostic code is probably caused by a short circuit to ground or a short circuit to another voltage source in the harness. The next likely cause is a problem with a sensor. The least likely cause is a problem with the ECM.
Note: The harness for the auxiliary temperature sensor includes a resistor assembly that is installed between the customer connector and the sensor connector. A short circuit across the resistor may cause active diagnostic codes for the sensor supply. Refer to Troubleshooting, "Auxiliary Temperature Sensor - Test" for a suspected problem with the resistor.
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| Illustration 1 | g01136632 |
Schematic for digital sensor supply | |
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The connection of any electrical equipment and the disconnection of any electrical equipment may cause an explosion hazard which may result in injury or death. Do not connect any electrical equipment or disconnect any electrical equipment in an explosive atmosphere. |
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Test Step 1. Inspect the Electrical Connectors and the Wiring
- Turn the keyswitch to the OFF position.
- Thoroughly inspect connectors (1), (2), and (3). Also inspect the connectors for the auxiliary temperature sensor and the coolant level sensor. Refer to Troubleshooting, "Electrical Connectors - Inspect".
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| Illustration 2 | g01136484 |
Top view (1) P1 ECM connector (2) P2 ECM connector (3) P3 Customer connetor | |
- Perform a 45 N (10 lb) pull test on each of the wires that is associated with the auxiliary temperature sensor circuit and with the coolant level sensor.
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| Illustration 3 | g01136655 |
P1 ECM connector (P1-24) Coolant level (P1-29) Digital return (P1-30) Analog return (P1-35) +8 V supply | |
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| Illustration 4 | g01136469 |
P2 ECM connector (P2-25) Auxiliary temperature sensor | |
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| Illustration 5 | g01136657 |
J3 and P3 connectors (8) +8 V supply (9) Digital return (11) Auxiliary temperature sensor (30) Analog return (30) Coolant level | |
- Check the torque of the allen head screws for the ECM connectors and the customer connector. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque values.
Expected Result:
All connectors, pins, and sockets are completely coupled and/or inserted, and the harness and wiring are free of corrosion, of abrasion, and of pinch points.
Results:
- OK - The connectors and wiring are in good repair. Proceed to Test Step 2.
- Not OK - There is a problem with the connectors and/or wiring.
Repair: Repair the wiring and connectors or replace the wiring and the connectors. Ensure that the seals are correctly installed on each of the connectors. Verify that the repair eliminates the problem.
STOP
Test Step 2. Check for Active Diagnostic Codes
- Connect the Caterpillar Electronic Technician (ET) to the service tool connector. Refer to Troubleshooting, "Electronic Service Tools".
- Turn the keyswitch to the ON position.
- Observe the active diagnostic code screen on Cat ET. Wait at least 15 seconds so that any codes may become active. Look for these codes:
- 263-03
- 263-04
- 263-03
Expected Result:
One of the above diagnostic codes is active:
Results:
- Active 263-03 code - A 263-03 diagnostic code is active. Proceed to Test Step 3.
- Active 263-04 code - A 263-04 diagnostic code is active. Proceed to Test Step 4.
- No active codes - None of the above codes are active.
Repair: If any of the above codes are logged and the engine is not running properly, refer to Troubleshooting, "Troubleshooting Without a Diagnostic Code".If the engine is running properly at this time, there may be an intermittent problem in a harness that is causing the codes to be logged. Refer to Troubleshooting, "Electrical Connectors - Inspect".
STOP
Test Step 3. Check the Sensor Supply Voltage at the Sensor Connectors
- Turn the keyswitch to the OFF position.
- Disconnect all of the following digital sensors at the sensor connector:
- Coolant level sensor J34/P34
- Auxiliary temperature sensor J114/P114
- Coolant level sensor J34/P34
- Turn the keyswitch to the ON position.
- Measure the voltage between terminal A and terminal B at the sensor connectors.
Expected Result:
The voltage is 8.0 ± 0.4 VDC at each of the sensor connectors.
Results:
- OK - The supply voltage is reaching the sensor.
Repair: Connect all of the sensor connectors. Clear all diagnostic codes. Check for active diagnostic codes. If the problem is intermittent, refer to Troubleshooting, "Electrical Connectors - Inspect".
STOP
- Not OK - At least one voltage measurement is not 8.0 ± 0.4 VDC. There is a problem with the wiring or with the ECM. Proceed to Test Step 5.
Test Step 4. Disconnect the +8 V Digital Sensors and Check for Active Diagnostic Codes
- Disconnect the following sensors one at a time:
- Engine coolant level
- Auxiliary temperature
- Engine coolant level
- Wait for 15 seconds after you disconnect each sensor. Check if the 263-04 diagnostic code has deactivated.
Expected Result:
The 263-04 diagnostic code deactivates when a particular sensor is disconnected.
Results:
- OK - The 263-04 diagnostic code deactivates when a particular sensor is disconnected.
Repair: Connect the suspect sensor. If the diagnostic code returns, replace the sensor.Connect all of the connectors. Verify that the problem is resolved.
STOP
- Not OK - The 263-04 diagnostic code remains after all of the sensors are disconnected. Leave the sensors disconnected. Proceed to Test Step 5.
Test Step 5. Check the +8 V Supply Wire for a Short Circuit
- Turn the keyswitch to the OFF position.
- Disconnect the J1/P1 and J2/P2 ECM connectors.
- Verify that all of the digital sensors are disconnected.
- Measure the resistance between P1-35 (+8 VDC supply) and the remaining terminals on the P1 and P2 connectors.
- Measure the resistance between P1-35 (+8 VDC supply) and the engine ground.
Note: Wiggle the harness during the following measurements in order to reveal any intermittent short condition.
Expected Result:
Each check of the resistance indicates an open circuit.
Results:
- OK - Each check of the resistance indicates an open circuit. The wires are not shorted. Proceed to Test Step 6.
- Not OK - At least one check of the resistance does not indicate an open circuit. One of the +8 V supply wires has a short circuit. There may be a problem with a connector.
Repair: Repair the wire and/or the connector, when possible. Replace parts, if necessary. Verify that the problem is resolved.
STOP
Test Step 6. Check the +8 V Supply and the Sensor Common for an Open Circuit
- Install a wire jumper between P1-35 +8 VDC supply and P1-29 digital sensor return.
- Measure the resistance between terminal A and terminal B at the connector for the coolant level sensor.
Note: Wiggle the harness during the following measurements in order to reveal any intermittent short condition.
- Install the wire jumper between terminal P1-35 (+8 V supply) and terminal P1-30 (analog sensor return).
- Measure the resistance between terminal A and terminal B at the connector for the auxiliary temperature sensor.
- Remove the wire jumpers.
Expected Result:
Each resistance measurement is less than ten Ohms.
Results:
- OK - Each resistance measurement is less than ten Ohms. The wires do not have an open circuit. Proceed to Test Step 7.
- Not OK - At least one resistance measurement is more than ten Ohms. A +8 V supply wire or a return wire has an open circuit. There may be a problem with a connector.
Repair: Repair the wires and/or the connector, when possible. Replace parts, if necessary. Verify that the problem is resolved.
STOP
Test Step 7. Check the +8 V Supply at the ECM
- Remove terminal 35 from the P1 ECM connector. Install a wire jumper with socket terminals on both ends into P1-35.
- Remove terminal 29 from the P1 ECM connector. Install a wire jumper with socket terminals on both ends into P1-30.
- Connect the P1 connector.
- Turn the keyswitch to the ON position.
- Measure the voltage between the wire jumpers in P1-35 and P1-29.
- Turn the keyswitch to the OFF position.
- Replace all wires to the original configuration.
Expected Result:
The voltage measurement is 8.0 ± 0.4 VDC.
Results:
- OK - The voltage measurement is 8.0 ± 0.4 VDC. The ECM is providing the correct voltage.
Repair: Clear all diagnostic codes. Check for active diagnostic codes. If the problem is intermittent, refer to Troubleshooting, "Electrical Connectors - Inspect".
STOP
- Not OK - The voltage measurement is not 8.0 ± 0.4 VDC. There is a problem with the ECM.
Repair: Replace the ECM. Refer to Troubleshooting, "Replacing the ECM".
STOP