ELBOW 7K2840 - Caterpillar

Illustration 1 g06142506
Connections of the service brake accumulator pressure sensor
This diagnostic code is associated with the service brake accumulator pressure sensor. This diagnostic code is recorded when the ECM reads the signal from the sensor as being shorted to the +battery. The sensor produces a Pulse Width Modulated (PWM) signal.Possible causes of the diagnostic code are listed below:
The supply circuit to the sensor is open.
The return circuit is open.
The signal circuit is shorted to the +battery.
The signal circuit is open or the sensor is disconnected.
The sensor has failed.
The ECM has failed. ECM failure is unlikely.Note: The following test procedure may create other diagnostic codes. Ignore these created diagnostic codes and clear the diagnostic codes when the original diagnostic code has been corrected. Ensure that the diagnostic code of CID 1961 FMI 03 is active before performing this procedure.Note: Use a digital multimeter for the measurements in this procedure.Test Step 1. CHECK THE VOLTAGE AT THE SENSOR.
Turn the disconnect switch and the key start switch to the ON position.
Disconnect the sensor from the machine harness.
At the machine harness connector for the sensor, measure the voltage between contact (A) (wire J850-WH(White)) and contact (B) (wire J879-GN(Green)).Expected Result:The voltage should measure less than 8V.Results:
OK - The voltage is less than 8V. Proceed to test step 4.
NOT OK - The voltage is greater than 8V.Repair: There is a problem with the machine harness or the ECM has failed. ECM failure is unlikely.Proceed to test step 2.Test Step 2. CHECK FOR AN OPEN IN THE SUPPLY CIRCUIT.
The key start switch and the disconnect switch remain in the ON position.
The sensor remains disconnected from the machine harness.
At the machine harness connector for the sensor, measure the voltage from contact A (wire J850-WH(White)) to ground.Expected Result:The voltage should measure approximately 8V.Results:
OK - The voltage measurement is approximately 8V. Proceed to test step 3.
NOT OK - The voltage does not measure approximately 8V.Repair: The supply circuit is not correct. Repair the circuit or replace the circuit.STOPTest Step 3. CHECK FOR AN OPEN IN THE RETURN CIRCUIT.
Turn the key start switch and the disconnect switch to the OFF position.
The sensor remains disconnected from the machine harness.
Disconnect the machine harness connector J1 from the ECM.
At the machine harness connector for the sensor, install a jumper wire from contact B (wire J879-GN(Green)) to ground.
At the machine harness connector for the ECM, measure the resistance from contact J1-12 (wire J879-GN(Green)) to ground.Expected Result:The resistance measurement should measure less than 5000 ohms.Results:
OK - The resistance measurement is less than 5000 ohms. The harness is correct.Repair: Check the circuit again. Perform a Wiggle Test on the machine wiring harness with the Cat® Electronic Technician (Cat ET). The Wiggle Test can detect the following in the machine wiring harness:
Momentary shorts
Intermittent shorts
OpensECM failure is unlikely. Exit this procedure and perform this procedure again. If the cause of the diagnostic code is not found, replace the ECM. Prior to replacing an ECM, always contact your dealership for possible consultation with Caterpillar. This consultation may greatly reduce