 | |
| Illustration 1 | g01282609 |
Schematic symbol for a typical pulse width modulated sensor (PWM) | |
Note: In addition to these tests, the Caterpillar Monitoring System diagnostics are helpful for troubleshooting sensors. Numeric readout mode shows a numeric value of the information from each sensor input. For a detailed explanation, refer to Systems Operation, "Numeric Readout Mode".
When you are testing a sensor, it is necessary to identify the connector contacts and the harness wires. The Electrical System Schematic shows the connector contact numbers and corresponding wire numbers. See the Electrical System Schematic in the Service Manual for the machine.
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| Illustration 2 | g01111831 |
Typical PWM square wave signal with various duty cycles. | |
| Tools Needed | ||
|---|---|---|
| 9U-7330 | Multimeter | 1 |
| 7X-1710 | Multimeter Probe Group | 1 |
Test Step 1. TROUBLESHOOT THE SENSORS.
Troubleshoot sensor circuits in the following order.
- Perform the Troubleshooting, "Sensor Signal Voltage" procedure. This procedure checks the sensor voltages at the sensor while the circuits remain connected. DISCONNECT NOTHING. Troubleshoot "as is" before disconnecting any circuits. Disconnecting circuits first may alter a poor connection. Proving the original cause of a problem may be difficult or impossible.
Expected Result:
The Troubleshooting, "Sensor Signal Voltage" procedure has determined the cause of the problem.
Results:
- OK - This test step has determined the cause of the problem.STOP
- NOT OK - This test step has NOT determined the cause of the problem. Proceed to test step 2.
Test Step 2. TROUBLESHOOT THE SENSORS
- Perform the Troubleshooting, "Sensor Dynamic Operation" procedure. This is an additional test. This will test the sensor during actual operating conditions.
Expected Result:
The Troubleshooting, "Sensor Dynamic Operation" procedure has determined the cause of the problem.
Results:
- OK - This test step has determined the cause of the problem.STOP
- NOT OK - This test step has NOT determined the cause of the problem.
Repair: If the sensor and the harness are correct, it is likely that the Machine ECM has failed. Replace the Machine ECM. See Testing and Adjusting, "Electronic Control Module (ECM) - Replace".
STOP