G3306B Petroleum Generator Set Engines Caterpillar

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

Table 1

Diagnostic Codes Table
Description	Conditions which Generate this Code	System Response
3217-3 Aftertreatment Intake %O2 : Voltage Above Normal	The Electronic Control Module (ECM) may have detected a short circuit to the +Battery. The ECM may have detected an open circuit in the signal circuit for the oxygen sensor at the turbocharger exhaust outlet.	The code is logged. The amber warning lamp is illuminated. The ECM uses the last good value from the oxygen sensor for the control of exhaust emissions.
3227-3 Aftertreatment Outlet %O2 : Voltage Above Normal	The ECM may have detected a short circuit to the +Battery. The ECM may have detected an open circuit in the signal circuit for the oxygen sensor at the outlet of the catalytic converter.

Illustration 1	g02037921
Schematic of the circuit for the oxygen sensor

Illustration 2	g02036913
Oxygen sensor and buffer (1) Oxygen sensor (2) Sensor buffer

The oxygen sensor is used to monitor the emission level of the engine exhaust. The ECM utilizes the signal from the oxygen sensor to adjust the air/fuel ratio. This strategy ensures that the engine burns the fuel efficiently. Two oxygen sensors are used for this application. One of the oxygen sensors is mounted in the turbocharger exhaust outlet. The other oxygen sensor is mounted in the output flange of the catalytic converter. Each sensor circuit consists of an oxygen sensor and a sensor buffer. A voltage converter is used to power both sensor circuits.

The oxygen sensor is used to detect the level of oxygen in the engine exhaust. The sensor generates a voltage signal that is directly proportional to the concentration of oxygen. The usable range of this signal is 150 mV to 750 mV. A lean concentration level will produce a 150 mV signal and a rich concentration level will produce a 750 mV signal. This analog signal is sent to the sensor buffer. The oxygen sensor utilizes a heating element in order to heat the sensing element of the sensor. The use of the heating element improves the warm-up time and the accuracy of the sensor.

Note: The sensor has an operating range of 600 to 800° C (1100 to 1500° F). The tip of the sensor may be hot. Use caution when you handle the oxygen sensor.

The sensor buffer is used to filter the electronic signal that is sent from the oxygen sensor. The buffer acts as a filter in order to condition the analog signal before the signal is sent to the ECM.

The voltage converter converts 24 VDC from the ECM to 12 VDC that is used by the sensor circuit. The voltage converter provides 12 VDC to each of the buffers. Each buffer supplies 12 VDC to the oxygen sensor. Each sensor supply is used to power the heating element and the supply circuit for the analog sensor.

A -3 diagnostic code indicates that a problem has been detected in the circuit for the sensor signal. The problem may be caused by the wiring, the sensor, the sensor buffer, or the voltage converter.

Illustration 3	g03431224
Location of the components for the oxygen level (right side engine view) (3) Oxygen sensor at the turbocharger exhaust outlet (4) Voltage converter (5) Buffer for the oxygen sensor at the turbocharger exhaust outlet (6) Buffer for the oxygen sensor at the outlet of the catalytic converter

Illustration 4	g02471161
Location of the oxygen sensor at the outlet of the catalytic converter (7) Oxygen sensor

Illustration 5	g02039033
Locations of the connectors at the ECM (typical right side engine view) (8) Harness connector that is for the sensors at the catalytic converter (9) J2/P2 ECM connectors (10) J1/P1 ECM connectors

Illustration 6	g02039053
Terminal locations at the J1/P1 ECM connectors that are for the oxygen level (P1-28) Supply for the voltage converter (P1-33) Signal return for the oxygen sensor at the outlet of the catalytic converter (P1-40) Keyswitch (P1-56) Signal for the oxygen sensor at the outlet of the catalytic converter

Illustration 7	g02039078
Terminal locations at the J2/P2 ECM connectors that are for the oxygen level (P2-44) Signal return for the oxygen sensor at the outlet of the catalytic converter (P2-54) Signal for the oxygen sensor at the outlet of the catalytic converter

Illustration 8	g02039098
Terminal locations at the harness connector for the sensors that are at the catalytic converter (Terminal J) 12 V return for the oxygen sensor at the outlet of the catalytic converter (Terminal K) Signal for the oxygen sensor at the outlet of the catalytic converter (Terminal L) 12 V supply for the oxygen sensor at the outlet of the catalytic converter (Terminal M) Signal return for the oxygen sensor at the outlet of the catalytic converter

Illustration 9	g02039196
Terminal locations at the connector for the buffer at the oxygen sensor (Terminal 1) 12 V supply (Terminal 2) 12 V return (Terminal 3) Signal (Terminal 4) Signal return

Illustration 10	g02039357
Terminal locations at the harness connector for the sensor buffer (Terminal 1) 12 V supply (Terminal 2) 12 V return (Terminal 3) Signal (Terminal 4) Signal return

Illustration 11	g02040215
Terminal locations at the voltage converter (Terminal 1) Keyswitch (Terminal 2) 24 V supply (Terminal 3) 24 V return (Terminal 5) 12 V supply (Terminal 6) 12 V return

Table 2

Troubleshooting Test Steps	Values	Results
1. Inspect the Electrical Connectors and the Wiring A. Turn the main disconnect switch to the OFF position. B. Thoroughly inspect the ECM connectors. Inspect all of the connectors that are associated with the circuit. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details. C. Perform a 45 N (10 lb) pull test on each of the wires in the ECM connectors that are associated with the circuit. D. Check the allen head screw for each of the ECM connectors for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details. E. Check the harness and wiring for abrasion and for pinch points from the actuator back to the ECM.	Connectors	Results: The harness and connectors appear to be OK. Proceed to Test Step 2. Results: The harness and connectors are Not OK. Repair: Repair the connectors or wiring and/or replace the connectors or wiring. Ensure that all of the seals are properly in place and ensure that the connectors are coupled. Verify that the repair eliminates the problem.
2. Check the Operation of the Heating Element for the Suspect Sensor A. Ensure that the electrical power has been removed from the engine. B. Turn the engine control to the STOP position. C. Remove the suspect sensor from the exhaust system. D. Allow several minutes for the heating element to heat. Use an infrared thermometer to check the temperature at the tip of the oxygen sensor. The heating element tip will heat the tip of the sensor to 600 to 800° C (1100 to 1500° F). E. Remove electrical power from the engine.	600 to 800° C (1100 to 1500° F)	Results: The heating element is heating the tip of the sensor to 600 to 800° C (1100 to 1500° F). Proceed to Test Step 7. Results: The tip of the sensor is not heating to the correct temperature. There is a problem with the heating element. The sensor may not be receiving the correct supply voltage. Proceed to Test Step 3.
3. Measure the Voltage from the Buffer at the Sensor Connector A. Disconnect the sensor connector that is between the tip of the sensor and the sensor buffer. B. Set the engine control to the STOP position. C. Use a multimeter to measure the voltage between terminal 1 (12 VDC) and terminal 2 (return) on the connector for the buffer. The connector is between the sensor and the sensor buffer. D. Remove electrical power from the engine.	12 VDC	Results: 12 V is available at the sensor connector. Supply voltage is available at the oxygen sensor. Repair: The heating element is not heating the sensor, but the sensor is receiving the correct voltage. There is a problem with the sensor. Replace the sensor. Verify that the repair eliminates the problem/ Results: 12 V is not available at the terminals of the sensor connector between the sensor and the sensor buffer. The supply voltage is not available at the sensor. There may be a problem with the sensor buffer or there may be a problem with the voltage converter. Proceed to Test Step 4.
4. Measure the Voltage from the Voltage Converter at the Harness Connector for the Sensor Buffer A. Disconnect the harness connector between the sensor buffer and the voltage converter. B. Set the engine control to the STOP position. C. Use a multimeter to measure the voltage between terminal 1 (12 VDC) and terminal 2 (return) at the sensor buffer. This measurement is taken on the harness side of the connector. D. Remove electrical power from the engine.	12 VDC	Results: There is 12 V available to the sensor buffer. Repair: Supply voltage is available at the input of the sensor buffer, but supply voltage is not available at the output of the sensor buffer. There is a problem with the sensor buffer. Replace the buffer. Verify that the repair eliminates the problem. Results: There is not 12 V available at the terminals of the engine harness connector at the sensor buffer. The supply voltage from the voltage converter is not available at the sensor buffer. There may be a problem in the wiring for the converter, or there may be a problem with the voltage converter. Proceed to Test Step 5.
5. Check the Output Voltage of the Voltage Converter A. Fabricate two jumper wires that are long enough to create a test circuit at the connector for the voltage converter. Crimp connector sockets to one end of each of the jumper wires. B. Disconnect the harness connector from the voltage converter. C. Remove the wires from terminal location 5 (12 VDC) and terminal location 6 (return) at the harness connector. Install a jumper wire into each of these terminal locations. D. Install the harness connector to the voltage converter. E. Set the engine control to the STOP position. F. Use a multimeter to measure the voltage between the two jumper wires. G. Remove electrical power from the engine. H. Restore the wiring to the original configuration.	12 VDC	Results: The supply voltage is available at the output of the voltage converter. Repair: Supply voltage is not available at the input of the sensor buffer, but supply voltage is available at the output of the voltage converter. There is a problem in the harness between the voltage converter and the buffer. Repair the harness or replace the harness. Verify that the repair eliminates the problem. Results: The supply voltage is not available at the output of the voltage converter. Repair: The supply voltage is not available at the output of the voltage converter. Proceed to Test Step 6.
6. Measure the Supply Voltage to the Voltage Converter A. Remove the harness connector from the voltage converter. B. Use a multimeter to measure the voltage between terminal 2 (24 VDC) and terminal 3 (−Battery).	24 VDC	Results: 24 VDC is not available between these two terminals, the problem may be in the supply wire between the ECM and the voltage converter. Repair: The problem may be in the return wire that is between the alternator ground and the voltage converter. Perform the necessary repairs. Verify that the repair eliminates the problem. Results: 24 VDC is available at the harness connector for the voltage converter, there is a problem with the voltage converter. Repair: Temporarily connect a new voltage converter to the harness connector. Test the new voltage converter for the proper output. If the output is correct, install the new component onto the engine.
7. Measure the Output Voltage of the Oxygen Sensor on the Terminals for the Sensor Signal A. Disconnect the sensor connector that is between the sensor and the sensor buffer. B. Remove the wires from terminal location 3 (signal) and terminal location 4 (signal return) on the sensor side of the connector. C. Set the engine control to STOP. D. Use a multimeter to measure the voltage between the loose ends of the wires for the sensor signal and sensor return at the oxygen sensor. E. Remove electrical power from the engine. F. Restore the wiring to the original configuration.	0.1 V to 0.9 V	Results: The signal voltage is between 0.1 and 0.9 V. The oxygen sensor is producing the correct voltage. The sensor is OK. Proceed to Test Step 8. Results: The signal voltage is not between 0.1 and 0.9 V. Repair: The oxygen sensor is not producing the correct voltage. There is a problem with the sensor. Replace the sensor. Verify that the repair eliminates the problem.
8. Measure the Output Voltage of the Sensor Buffer at the Terminals for the Sensor Signal A. Disconnect the harness connector that is between the sensor buffer and the ECM. B. Remove the wires from terminal location 3 (signal) and terminal location 4 (signal return) on the buffer side of the harness connector. C. Set the engine control to STOP. D. Use a multimeter to measure the voltage between the loose ends of the wires for the sensor signal and sensor return at the sensor buffer. E. Remove electrical power from the engine. F. Restore the wiring to the original configuration.	Signal Voltage	Results: The signal voltage from the sensor buffer is comparable to the signal voltage from the sensor. Repair: The signal voltage at the output of the sensor buffer is OK. There is a problem in the harness between the sensor buffer and the ECM. Check for continuity in the wire for the sensor signal and the wire for the signal return. Repair the harness or replace the harness. Verify that the repair eliminates the problem. Results: The signal voltage out of the buffer is not comparable to the signal voltage from the sensor. Repair: The sensor buffer is not processing the sensor signal correctly. There is a problem with the sensor buffer. Replace the sensor buffer. Verify that the repair eliminates the problem.