Troubleshooting Method For Open Circuit In Wiring Harness Of Pressure Sensor System - Komatsu PC88MR-10 Shop Manual

40 Troubleshooting
Related information on troubleshooting
Troubleshooting method for open circuit in wiring harness of pressure
sensor system
a Since the pressure sensors consist of not only resistor but also electronic circuit components such as
amplifiers they have variation in measured value and their own polarities. So troubleshooting must be
performed carefully.
Failure codes applicable to this diagnosis
CA123: Charge air pressure sensor low error
Procedure
1. Measure and record resistance of pressure sensor unit.
1) Disconnect pressure sensor connector (1) and connect socket (2) to the sensor side connector.
2) Measure resistances R1 and R2 between pins.
a If the polarities of multimeter probes to apply are reversed, measured values may change.
Therefore, when measuring the resistances in steps 1 and 2, apply the multimeter probes to the
pressure sensor connector so that their polarities match those of the sensor.
a If the measured value is infinite, take measurements by applying the probes of the opposite
polarities and record the finite value obtained as a measured value.
a Since the measured values may be dispersed, take several measurements.
The cause of this dispersion appears to be an electric charge in a sensor. Take measurements
several times in steps 1 and 2. Consider this dispersion when judging whether or not the wiring
harness is open in step 3.
2. Measure and record the resistance of the wiring harness between the pressure sensor and engine
controller connected.
1) Since 5 V power supply to the pressure sensor is supplied to other sensors, disconnect other sensor
connectors first. (*)
2) With the pressure sensor to measure connected, disconnect connector (3) on the engine controller
side, and connect T-adapter (4) to the wiring harness side connector.
3) Connect T-box (5) to T-adapter (4) and measure resistances R1' and R2' between respective pins.
3. Judging open circuit
If there is an "apparent difference" between resistances R1 and R2 measured in step 1 and resistances
R1' and R2' measured in step 2, the "wiring harness is open".
a "Apparent difference" means a difference of 10 or more times.
40-44
(D65-E720-42A-P-00-A)
PC88MR-10