Komatsu PC200-8M0, Shop Manual

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SEN06132-01
PC200, 200LC, 220, 220LC-8M0 40-200
63
200 General Information on troubleshooting
Troubleshooting method for open circuit in wiring harness of pressure sensor system
Troubleshooting method for open circuit in wiring harness of pressure
sensor system
a
Since pressure sensors consisting not only of resistor but also electronic circuit components such as am-
plifiers have variation in measured value and its own polarities. So troubleshooting must be performed
carefully.
Failure codes applicable to this diagnosis
q
CA123: Charge air pressure sensor low error
q
CA451: Common rail pressure sensor high 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 polarities of multimeter probes to apply are reversed, measured values may change. Therefore,
when measuring resistances in steps 1 and 2, apply the multimeter probes to the pressure sensor
connector so that their polarities match these of the sensor.
a
If measured value is infinite, take measurements by applying the probes of opposite polarities and
record the finite value obtained as a measured value.
a
Since measured values may be dispersed, take several measurements.
Cause of this dispersion appears to be a charge in a sensor. Repeat steps 1 and 2 several times.
Consider this dispersion when judging whether the wiring harness is open in step 3.
2. Measure and record resistance with 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 engine controller side,
and connect T-adapter (4) to the 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, "wiring harness is open".
a
"Apparent difference" means a difference of 10 or more times.