HOSE 3718946 - Caterpillar

MID 087 - Chassis ECMCID 0849 - System Air Pressure SensorFMI 04 - Voltage Below Normal
Illustration 1 g01883713
System air pressure sensor circuit
This diagnostic code indicates the "Chassis" ECM detects system air pressure sensor voltage is below normal.The pressure sensor has the following characteristics:
Pulse width modulation (PWM) type of sensor
Operating duty cycle from 0% to 100%
Operating pressure range from 0 kPa (0 psi) to 1135 kPa (164 psi)
Pressure and duty cycle relationship is linearThe following can cause this code:
Sensor signal circuit shorted to ground
Sensor failure
ECM failureNote: The following test procedure may create other diagnostic codes. Ignore these created codes and clear these created codes after the original diagnostic code has been corrected. Ensure diagnostic code CID 0849 FMI 04 is active before performing this procedure.Note: Use a calibrated digital multimeter for this procedure.Test Step 1. CHECK THE SENSOR
Turn on the disconnect switch and the key switch.
Disconnect the sensor from the harness while observing the diagnostic code status.Expected Result:CID 0849 FMI 04 does not change and remains active.Results:
OK - CID 0849 FMI 04 does not change and remains active. Proceed to Test Step 2.
NOT OK - CID 0849 FMI 04 changes and is not active. The sensor has failed.Repair: Replace the sensor.STOPTest Step 2. CHECK FOR A SHORT TO GROUND
Turn off the key switch and the disconnect switch.
Disconnect the harness from the sensor.
Disconnect the harness connectors from the ECM.
At the harness connector for the ECM, measure the resistance from the signal contact J2-32 (wire M914-WH(White)) of the harness to all possible sources of ground. Measure the resistance to all contacts of the harness connectors for the ECM.Expected Result:Each resistance is greater than 5000 ohms.Results:
OK - Each resistance is greater than 5000 ohms. Proceed to Test Step 3.
NOT OK - A resistance is less than 5000 ohms. There is a short between signal contact J2-32 (wire M914-WH(White)) and the circuit with low resistance.Repair: Repair or replace the harness.STOPTest Step 3. CHECK THE DIAGNOSTIC CODEThe key switch and the disconnect switch remain in the off position.
Inspect the harness.Clean the harness connector contacts.Inspect the harness connector contacts for corrosion or damage.Inspect the wire insulation for damage caused by heat, corrosion, or chafing.
Perform a 45 N (10 lb) pull test on each circuit wire.
Reconnect all harness connectors.Verify that the connectors are fully seated and the clips are fastened.
Check for intermittent problems. Using Cat® Electronic Technician (Cat® ET), perform a wiggle test on the harness.
Turn on the disconnect switch and the key switch.
Operate the machine.
Check CID 0849 FMI 04 status.Expected Result:CID 0849 FMI 04 is not active.Results:
OK - CID 0849 FMI 04 is not active.Repair: The initial diagnostic code was probably caused by a poor connection at one of the connectors that was checked.Resume normal operation.STOP
NOT OK - CID 0849 FMI 04 is active.Repair: Exit this procedure and perform this procedure again. Contact the technical communicator at your Caterpillar dealer. If the ECM requires replacement, see Testing and Adjusting, "Electronic Control Module (ECM) - Replace".STOP