TUBE AS 2048740 - Caterpillar

Procedure For Troubleshooting PWM Sensor Problems
It is recommended the third Reference be used for troubleshooting temperature, pressure, and fuel level sensor problems for both VFD and LCD CMS machines because it contains later data and procedures.1. Verify the sensor is working AT THE SENSOR by checking between the sensor and the sensor's connector (see the References). This step should be performed with the CMS control connected just as it would be when arriving on the job location.2. Probe through the sensor wire insulation or use the 7X1710 Probe Cable Group to probe into the connector through the connector grommet beside the lead wires. If the signal wire from the sensor to the CMS control is open, the signal voltage measured at the sensor will be the same as the reference chart for Sensor Dynamic Test (CMS disconnected) in the third Reference on Page 64.3. Verify the condition of the wiring harness by checking between the sensor's connector and the sensor:A. If there is no sensor signal detected in Step 2, check for both power and ground with the sensor connected.B. Check the signal circuit. 1. If the sensor is working according to the test performed in Step 1, check for sensor signal voltage on the CMS or AEIS side of the sensor connector. If the signal voltage is the same on both sides of this connector, the problem is not in the connector. Proceed to the next step.2. To check the signal harness wire from the CMS or AEIS to the sensor, disconnect the sensor at the sensor connector. Measure the voltage from the machine harness connector signal contact to the ground contact. Voltage should equal + 5 .5 volts. A value less than this indicates an open in this wire. A value greater than this indicates a short to the positive side of the battery. It is VERY IMPORTANT to make sure the previous steps are completed before performing the next step.4. If both the sensor and wiring harness test correctly, the CMS control is most likely the cause.In Summary:
Intermittent problems are the most difficult to locate and verify. The service technician must remember that with PWM sensors: an open wiring harness, a short on the positive side of the battery, a short to ground, or very poor connections, can sometimes be very difficult to find. Any one or more of the previous conditions will cause the CMS or AEIS control to store a service code for incorrect temperature, low oil pressure, or a similar fault condition.
ALSO, WITH CMS, THE OPERATOR SEES A THAT AGREES WITH THAT GAUGE. This means the gauge will flash and show in the red (high or low). If required, the action light will flash and the action alarm will sound. At this stage, the operator does not know if the machine system is causing the warning or a CMS fault exists, but the warning must be treated as appropriate for the warning indicated. CMS is the most reliable