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G3520B Industrial Engines Caterpillar


Nitrogen Oxide Level - Test

Usage:

G3520B GLF
System Operation Description:

Use this procedure to troubleshoot the electrical system if a problem is suspected with the NOX sensor group. Also, use this procedure if one of the diagnostic codes or the event code in Table 1 is active or easily repeated.

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Table 1
Diagnostic Codes Table    
Description     Conditions which Generate this Code     System Response    
3002-2 Engine Exhaust NOx Level Sensor : Erratic, Intermittent, or Incorrect     The Electronic Control Module (ECM) has received a communication that indicates that the data from the NOX sensor is incorrect.     The power to the sensor is turned off.
NOX feedback is turned off.
The fuel correction factor is locked at the last value that is known to be good.
The code is logged.
The alarm output is activated.    
3002-9 Engine Exhaust NOx Level Sensor : Abnormal Update Rate     The ECM has not received several messages that were expected from the NOX sensor over the CAN data link.     NOX feedback is turned off.
The fuel correction factor is locked at the last value that is known to be good.
The code is logged.
The alarm output is activated.    
3002-12 Engine Exhaust NOx Level Sensor : Failure     The ECM has received communications from the NOX sensor that indicates that an internal fault has been detected.     NOX feedback is turned off.
The fuel correction factor is locked at the last value that is known to be good.
The code is logged.
The alarm output is activated.
The shutdown output is activated.
The engine is shut down.    
E717(1) Engine Exhaust NOx Level Sensor Operating Temperature Not Reached     The ECM has not received a communication that is expected from the NOX sensor. The communication reports that the operating temperature of the sensor has been reached.     NOX feedback is turned off.
The fuel correction factor is locked at the last value that is known to be good.
The code is logged.
The alarm output is activated.    

The NOX sensor group is used by the ECM to measure the level of NOX concentration in the engine exhaust. This value is reported back to the ECM via the CAN data Link. The ECM uses this information to control the air/fuel ratio for the engine. By controlling the air/fuel ratio, the ECM is able to control the engine operation for optimum performance at reduced exhaust emissions.

The NOX sensor group is made up of two separate components:

Sensor - The NOX sensor consists of a ceramic element that measures the concentration of NOX in the exhaust gas. The sensor contains a heating element that is used to heat the sensor to approximately 800 °C (1450 °F). Once the heating element reaches this temperature, the sensor begins sending NOX data to the sensor buffer.

Sensor buffer - The sensor buffer is used to process the signals that are received from the sensor. The buffer transmits this information to the ECM via the CAN data link. The buffer also reports diagnostic data to the ECM over the CAN data link. The sensor buffer is powered through a Pulse Width Modulated output (PWM output) by the ECM. The sensor buffer requires 18 to 36 V in order to operate.

The buffer is powered by the ECM after the following conditions are verified:

  • No diagnostic codes related to the NOX sensor are active

  • Engine speed above 500 rpm

The sensor and the sensor buffer are integrated parts. The sensor and the sensor buffer must be replaced as a single component, if necessary.

An active diagnostic code is probably caused by a problem with a connector or harness for the CAN data link or the power supply. The next likely cause is a problem with the NOX sensor group. The least likely cause is a problem with the ECM.

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Illustration 1g01592466

Schematic of the circuit for the NOX sensor

Test Step 1. Inspect the Electrical Connectors and the Wiring

  1. Set the engine control switch to the OFF/RESET position. Remove the electrical power from the engine.
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    Illustration 2g01418482

    Location of the components for the NOX sensor (typical rear engine view)

    (1) NOX sensor group

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    Illustration 3g01418490

    Locations of the connectors for the NOX sensor (typical left side engine view)

    (2) J2/P2 ECM connectors for the master ECM

    (3) J1/P1 ECM connectors for the master ECM

    (4) J8/P8 control harness connectors at the terminal box for the master ECM

  1. Thoroughly inspect the condition of connectors for NOX sensor (1). Also, thoroughly inspect the condition of ECM connectors (2) and (3), and control harness connectors (4). Refer to Troubleshooting, "Electrical Connectors - Inspect".
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    Illustration 4g01412137

    Terminal connections at the P1 ECM connector that are for the NOX sensor

    (P1-34) CAN data link −

    (P1-42) CAN shield

    (P1-50) CAN data link +

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    Illustration 5g01418571

    Terminal connections at the P2 ECM connector that are for the NOX sensor

    (P2-63) PWM output (24 V)

    (P2-64) Return

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    Illustration 6g01418503

    Terminal locations at the P8 connector that are for the NOX sensor

    (P8-h) CAN shield

    (P8-C) PWM output (24 V)

    (P8-P) Return

    (P8-O) CAN data link +

    (P8-Y) CAN data link −

    Show/hide table

    Illustration 7g01418510

    Terminal locations at the harness connectors that are for the NOX sensor

    (Terminal 1) PWM input (24 V)

    (Terminal 2) Return

    (Terminal 3) CAN Data Link −

    (Terminal 4) CAN Data Link +

  1. Perform a 45 N (10 lb) pull test on each of the wires in the circuit for the NOX sensor.

  1. Check the torque of the allen head screws for each of the ECM connectors and of the engine interface connector. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque values.

  1. Check the harness and the wiring for abrasion and for pinch points from the battery to the junction box. Check that the fuses for the circuit are not blown.

Expected Result:

All of the connectors, pins, and sockets are connected properly. The connectors and the wiring do not have corrosion, abrasion, or pinch points.

Results:

  • OK - The connectors and the wiring appear to be OK. Proceed to Test Step 2.

  • Not OK - The components are not in good repair and/or at least one connection is improper.

    Repair: Perform the necessary repairs and/or replace parts, if necessary. Ensure that all of the seals are properly installed. Ensure that the connectors are properly engaged. Verify that the repair has eliminated the original problem.

    STOP

Test Step 2. Check for Active Diagnostic Codes and Event Codes

  1. Connect the Caterpillar Electronic Technician (ET) to the service tool connector.

  1. Restore the electrical power to the engine. Set the engine control switch to the STOP position. Start the engine. Allow the engine to reach the normal operating temperature.

  1. Check for the following active codes:

    • 3002-2 Engine Exhaust NOx Level Sensor erratic, intermittent, or incorrect

    • 3002-9 Engine Exhaust NOx Level Sensor abnormal update rate

    • 3002-12 Engine Exhaust NOx Level Sensor failure

    • E717 Engine Exhaust NOx Level Sensor Operating Temperature Not Reached

    Note: Monitor the active diagnostic codes and the event codes on Cat ET. Wait at least 30 seconds in order for diagnostic codes to become active.

  1. Shut down the engine. Set the engine control switch to the OFF/RESET position. Remove the electrical power from the engine.

Expected Result:

There is not an active code for the NOX sensor at this time.

Results:

  • OK - There is not an active code for the sensor at this time.

    Repair: There does not appear to be a problem in the circuits of the NOX sensor at this time. If one of these codes is logged there may be an intermittent problem with one of the circuits. If there is a logged code, or an intermittent electrical problem is suspected, refer to Troubleshooting, "Electrical Connectors - Inspect" for information that is related to troubleshooting intermittent electrical problems.

    STOP

  • Active 3002-2 - A 3002-2 diagnostic code is active at this time.

    Repair: The NOX sensor reported that the data from the sensor is incorrect. Perform the following procedure:

    1. Check the stability of the engine:

      1. Start the engine. Allow the engine to warm to operating temperature.

      1. Use Cat ET to monitor the engine rpm for a two minute period.

        Check that the engine rpm remains stable within ten rpm from the engine speed setpoint that is given in Cat ET.

        An unstable engine rpm can cause the NOX concentrations in the exhaust to become unstable. A 3002-2 diagnostic code may become active. Troubleshoot the engine for the unstable engine rpm before you continue with this procedure.

      1. Use Cat ET to check the value of the intake manifold pressure.

        If the intake manifold pressure is less than 90 kPa (13 psi), the 3002-2 diagnostic code may become active. Troubleshoot the engine for a low intake manifold pressure before you continue with this procedure.

    1. Ensure that the engine control switch is in the OFF/RESET position. Allow the engine to cool.

    1. Use a paint stick to mark the orientation of the NOX sensor in the exhaust stack.

    1. Remove the sensor from the exhaust stack.

    1. Inspect the sensor for deposits that may be covering the holes that are in the body of the sensing element. Clean the body of the sensing element, if necessary.

    1. Install the sensor into the exhaust stack. During the installation, use the markings that are from the paint stick to orient the sensor. Provide the sensor with an orientation that is approximately 90 degrees from the previous orientation.

    1. Start the engine. Allow the engine to warm to operating temperature.

    1. Use Cat ET to monitor active diagnostic codes for the NOX sensor.
    If the original diagnostic code is no longer active, the problem has been resolved. Return the engine to service.If the 3002-2 diagnostic code remains active, replace the sensor group. Verify that the repair eliminates the original problem.

    STOP

  • Active 3002-9 - A 3002-9 diagnostic code is active at this time. The ECM has detected a problem with the communication between the ECM and the sensor. Proceed to Test Step 3.

  • Active 3002-12 - A 3002-12 diagnostic code is active at this time.

    Repair: The NOX sensor reported an internal fault to the ECM. Replace the sensor group. Verify that the repair eliminates the original problem.

    STOP

  • Active E717 - A E717 diagnostic code is active at this time.

    Repair: Check if the following diagnostic codes are active:

    • 3002-2

    • 3002-12

    If these diagnostic codes are active, troubleshoot the other codes before continuing.If other codes that are related to the NOX sensor are not active, there is a problem with the sensor. Replace the sensor group. Verify that the repair eliminates the original problem.

    STOP

Test Step 3. Check for Electrical Power at the Harness Connector for the Sensor Group

  1. Disconnect the harness connector at the buffer for the NOX sensor.

  1. Start the engine.

    Note: The engine speed must be greater than 500 rpm for the sensor buffer to be powered.

  1. Measure the voltage between terminals 1 (PWM input) and 2 (return) at the harness connector for the sensor group.

  1. Set the engine control switch to the OFF/RESET position. Remove the electrical power from the engine.

  1. Restore the wiring to the original configuration.

Expected Result:

The voltage at the harness connector is 24 ± 4 V.

Results:

  • OK - The voltage at the harness connector is 24 ± 4 V.

    Repair: The NOX sensor is receiving the proper operating voltage from the ECM. There is a problem with the sensor. Replace the sensor group. Verify that the repair eliminates the original problem.

    STOP

  • Not OK - The voltage at the harness connector is not within specifications. The sensor is not receiving the proper operating voltage. Proceed to Test Step 4.

Test Step 4. Check for Electrical Power at the ECM

  1. Ensure that the engine control switch is in the OFF/RESET position.

  1. Disconnect the J2/P2 ECM connector.

  1. Fabricate two jumper wires that are long enough to create a test circuit at the J2 ECM connector. Crimp connector sockets to one end of each of the jumper wires.

  1. Remove the wires from terminal locations P2-63 (PWM output) and P2-64 (return) at the ECM connector. Install a jumper wire into each of these terminal locations.

    Note: Ensure that the loose ends of the jumper wires do not contact any ground source. Also, ensure that the loose ends of the jumper wires do not become connected.

  1. Connect the J2/P2 ECM connectors.

  1. Start the engine.

    Note: The engine speed must be greater than 500 rpm for the sensor buffer to be powered.

  1. Measure the voltage between the loose ends of the jumper wires.

  1. Set the engine control switch to the OFF/RESET position. Remove electrical power from the engine.

  1. Restore the wiring to the original configuration.

Expected Result:

The voltage at the ECM connector is 24 ± 4 V.

Results:

  • OK - The voltage at the ECM connector is 24 ± 4 V.

    Repair: The voltage is correct at the ECM. There is a problem in the control harness or in a connector. Perform the necessary repairs to the harness and/or connectors. Verify that the repair eliminates the original problem.

    STOP

  • Not OK - The voltage at the ECM connector is not 24 ± 4 V.

    Repair: The voltage at the ECM is not within specifications. There is a problem with the ECM. Perform the following procedure:

    1. Temporarily connect a new ECM.

      Refer to Troubleshooting, "ECM - Replace " for details.

    1. Recheck the circuit in order to ensure that the original problem has been resolved.

      If the problem is resolved with the new ECM, install the suspect ECM. If the problem returns with the suspect ECM, replace the ECM. Verify that the problem is resolved.

      If the problem is not resolved with the new ECM, install the original ECM. There is a problem in the wiring.

    STOP

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