Posted on by

Electronic Control System Gas Plus Engines – FAULT CODE 752 – B and C Gas Plus

Heated Oxygen Sensor Error

View Related Topic

Overview

CODE REASON EFFECT
Fault Code: 752
PID: S065
SPN: 723
FMI: 2
LAMP: Amber
SRT: 

Heated Oxygen Sensor Error. The sensed air fuel ratio does not match the desired air fuel ratio.

Possible reduced performance. No closed-loop operation.

Heated Oxygen Sensor Circuit
SMALL | MEDIUM | LARGE

Circuit Description

The electronic control module (ECM) uses this sensor to determine the composition of the exhaust gas and then, to adjust fueling.

Component Location

The heated oxygen sensor is located in the exhaust outlet connection, after the turbocharger.

Shop Talk

This fault is not typically caused by a failed heated oxygen sensor, but is a result of the engine running very lean or very rich. To determine if the engine is rich or lean, monitor the heated oxygen sensor compensation in INSITE™ electronic service tool.

Cautions and Warnings

 WARNING 

Do not touch the heated oxygen sensor until it has cooled. The heated oxygen sensor operates at high temperature and can cause personal injury.
 CAUTION 

Do not use any lubricant in the heated oxygen sensor connector. The sensor will not perform correctly with any grease in the connector.
 CAUTION 

To reduce the possibility of damaging a new ECM, all other active fault codes must be investigated prior to replacing the ECM.

Troubleshooting Steps

STEPS SPECIFICATIONS
STEP 1. Check the fault codes.  
  STEP 1A. Check for multiple fault codes. Fault Codes 453, 454, 455, 511, and/or 751 active?
  STEP 1B. Check for an inactive fault code. Fault Code 752 inactive?
STEP 2. Check the fuel system.  
  STEP 2A. Verify secondary fuel pressure. Is pressure correct for the engine family?
  STEP 2B. Check for a stuck open or sticking fuel control valve. Secondary fuel pressure drop within 50 seconds of key on?
  STEP 2C. Gas Mass Flow Compensation correct. Is the gas flow compensation a positive 25 or higher?
STEP 3. Check Base engine components.  
  STEP 3A. Check for an exhaust leak. Any exhaust leaks?
STEP 4. Check the engine harness and heated oxygen sensor.  
  STEP 4A. Check the engine harness and heated oxygen sensor connector pins. Dirty or damaged pins?
  STEP 4B. Check for an open circuit in the heated oxygen sensor. 2.9 to 3.7 ohms at room temperature?
  STEP 4C. Check the heated oxygen sensor heater supply voltage. Voltage greater than 12 VDC?
  STEP 4C-1. Check for an open circuit in the engine harness.
  STEP 4D. Check for an open circuit in the engine harness. Less than 10 ohms?
  STEP 4E. Check for pin short to ground in the engine harness. Less than 10 ohms?
  STEP 4F. Check for a pin to pin short circuit in the engine harness. Greater than 100k ohms?
  STEP 4G. Verify oxygen sensor operation. Did the sensor pass the test?
STEP 5. Clear the fault codes.  
  STEP 5A. Disable the fault code. Fault Code 752 inactive?
  STEP 5B. Clear the inactive fault codes. All fault codes cleared?

Guided Step 1 – Check the fault codes.

Guided Step 1A – Check for multiple fault codes.

Conditions

  • Turn keyswitch ON
  • Connect INSITE™ electronic service tool..

Action

Check for multiple fault codes.

  • Use INSITE™ electronic service tool to read the fault codes.

Fault Codes 453, 454, 455, 511, and/or 751 active?
YES NO

Troubleshoot any remaining fault codes before proceeding.

 No Repair
Fault Codes 453, 454, 455, 511, or 751 first.

Guided Step 1B – Check for an inactive fault code.

Conditions

  • Turn keyswitch ON
  • Connect INSITE™ electronic service tool.

Action

Check for an inactive fault code.

  • Use INSITE™ electronic service tool to read the fault codes.

Fault Code 752 inactive?
YES NO
No Repair No Repair
Procedure 019-362

Guided Step 2 – Check the Fuel System.

Guided Step 2A – Verify secondary fuel pressure.

Conditions

  • Connect all components
  • Turn keyswitch OFF
  • Connect INSITE™ electronic service tool.

Action

Monitor the secondary fuel pressure.

  • Use INSITE™ electronic service tool to monitor the fuel pressure.
  • Secondary fuel pressures are different depending on engine platform. See below:

B Gas Plus – 60 psia Minimum

B LPG Plus – 40 psia Minimum

C Gas Plus – 75 psia Minimum

Note: All pressure sensors on the Gas Plus engines are absolute pressure sensors.

Note: It might be necessary to perform a stall test to monitor dynamic secondary fuel pressure. If fuel pressure is not adequate, then the engine will surge under load, possibly causing this fault to occur. Refer to the Engine Performance Troubleshooting Tree in Section TT.

Is pressure correct for the engine family?
YES NO
No Repair

Refer to the Engine Performance Troubleshooting Tree in Section TT.

Guided Step 2B – Check for a stuck open fuel control valve.

Conditions

  • Turn keyswitch ON
  • Connect INSITE™ electronic service tool.

Action

Check for a stuck fuel control valve.

  • Use INSITE™ electronic service tool to monitor the secondary fuel pressure while keyswitch is on.

Note: If the fuel control valve is stuck open, raw fuel will be dumped into the engine and out the exhaust. This will cause the heated oxygen sensor to read a lower than actual air oxygen value.

Secondary fuel pressure drop within 50 seconds of keyswitch on?
YES NO

A defective fuel control valve has been detected.

Replace the fuel control valve. Refer to Procedure 019-102.

Use INSITE™ electronic service tool to reset the fuel tables.

 No Repair

Guided Step 2C – Gas Mass Flow Compensation incorrect.

Conditions

  • Connect all components
  • Turn keyswitch ON
  • Connect INSITE™ electronic service tool
  • Run engine at stall conditions.

Action

Monitor the gas mass flow compensation.

  • Use INSITE™ electronic service tool to monitor the gas mass flow compensation.

Note: Oil contamination of the gas mass flow sensor will cause a low flow reading and over-compensate for fuel flow. If the engine is running rich and a Fault Code 752 is active, the gas mass flow sensor must
be inspected. Check the fuel filter for excess oil due to improper maintenance. If there is more than one ounce of oil in the fuel filter, there is a possibility that oil has contaminated the fuel system. The customer will need to check their gas compression station for oil carry over.

Is the gas flow compensation a positive 25 or higher?
YES NO

Replace the gas mass flow sensor. Refer to Procedure 019-101.

Use INSITE™ electronic service tool to reset the fuel tables.

 No Repair

Guided Step 3 – Check base engine components.

Guided Step 3A – Check an exhaust leak.

Conditions

  • Turn keyswitch OFF.

Action

Check for an exhaust leak between the exhaust manifold and the heated oxygen sensor.

  • Check all gaskets
  • Check all castings
  • Check all pipe plugs.

Any exhaust leaks?
YES NO

An exhaust leak has been detected.

Repair or replace any exhaust component. Refer to Procedure 011-007 in the B5.9G, B5.9 LPG, B Gas Plus and B LPG Plus Troubleshooting and Repair Manual, Bulletin 3666164 and 011-007 in the C8.3g, C Gas Plus and L Gas Plus Troubleshooting and Repair Manual, Bulletin 3666206.

 No Repair

Guided Step 4 – Check the engine harness and heated oxygen sensor.

Guided Step 4A – Inspect the engine harness and heated oxygen sensor connector pins.

Conditions

  • Turn keyswitch OFF
  • Disconnect engine harness connector 2 from the ECM.
  • Disconnect the heated oxygen sensor from the engine harness.

Action

Inspect the engine harness connector 2 and heated oxygen sensor connector pins for the following:

  • Loose connector
  • Corroded pins
  • Bent or broken pins
  • Pushed back or expanded pins
  • Moisture in or on the connector
  • Missing or damaged connector seals
  • Dirt or debris in or on the connector pins
  • Connector shell broken
  • Wire insulation damage
  • Damaged locking tab connector.

For general inspection techniques, refer to Components Connector and Pin Inspection, Procedure 019-361.

Dirty or damaged pins?
YES NO

Repair the damaged pins. Replace the engine harness, or replace the sensor, whichever has the damaged pins.

  • Flush the dirt, debris, or moisture from the connector pins using electronic contact cleaner, Part Number 3824510.
  • Repair the engine harness. Refer to Procedure 019-204.
  • Replace the engine harness. Refer to Procedure 019-043.
  • Replace the heated oxygen sensor. Refer to Procedure 019-100.
 No Repair

Guided Step 4B – Check for an open circuit in the heated oxygen sensor.

Conditions

  • Turn keyswitch OFF
  • Disconnect the heated oxygen sensor from the engine harness.

Action

Check heated oxygen sensor resistance.

  • Measure the resistance between the heated oxygen sensor heater SUPPLY pin and the heated oxygen sensor heater RETURN pin at the heated oxygen sensor connector.
  • Make sure to check the resistance at room temperature (23°C [73°F]
    ± 5 degrees).

Refer to the circuit diagram or wiring diagram for connector pin identification.

For general resistance measurement techniques, refer to Resistance Measurements Using a Multimeter and Wiring Diagram, Procedure 019-360

2.9 to 3.7 ohms at room temperature?
YES NO
No Repair

Replace the heated oxygen sensor. Refer to Procedure 019-100.

Use INSITE™ electronic service tool to reset the fuel tables.

Guided Step 4C – Check the heated oxygen sensor heater supply voltage.

Conditions

  • Turn keyswitch ON
  • Disconnect the heated oxygen sensor from the engine harness.

Action

Check the voltage at the heated oxygen sensor connector at the engine harness.

  • Measure the voltage between the heated oxygen heater SUPPLY pin and the heated oxygen heater RETURN pin at the engine harness.

Refer to the circuit diagram or wiring diagram for connector pin identification.

Voltage greater than 12 VDC?
YES NO
No Repair No Repair

Guided Step 4C-1 – Check for an open circuit in the engine harness.

Conditions

  • Turn keyswitch OFF
  • Disconnect engine harness connector 1 from the ECM.
  • Disconnect the heated oxygen sensor from the engine harness.

Action

Check for an open circuit.

  • Measure the resistance between the engine harness ECM connector 1 heated oxygen heater RETURN pin and the engine harness heated oxygen sensor connector RETURN pin.

Refer to the circuit diagram or wiring diagram for connector pin identification.

For general resistance measurement techniques, refer to Resistance Measurements Using a Multimeter and Wiring Diagram, Procedure 019-360

Less than 10 ohms?
YES NO

Check for a blown, corroded or wet fuse in the heated oxygen heater supply line in the OEM harness.

Check for an open circuit in the OEM switched battery supply to the heated oxygen sensor supply.

Repair the damaged pins. Replace the engine harness or OEM harness, whichever has the damaged pins.

  • Flush the dirt, debris, or moisture from the connector pins using electronic contact cleaner, Part Number 3824510.
  • Repair or replace the OEM harness. Refer to Procedure 019-071.
  • Repair or replace the 10 Ampere heater supply fuse. Refer to 019-198.
  • Repair the engine harness. Refer to Procedure 019-204.
  • Replace the engine harness. Refer to Procedure 019-043.

An open return circuit has been detected in the engine harness.

Repair or replace the engine harness.

  • Repair the engine harness. Refer to Procedure 019-204.
  • Replace the engine harness. Refer to Procedure 019-043.

Guided Step 4D – Check for an open circuit in the engine harness.

Conditions

  • Turn keyswitch OFF
  • Disconnect engine harness connector 2 from the ECM.
  • Disconnect the heated oxygen sensor from the engine harness.

Action

Check for an open circuit.

  • Measure the resistance between the engine harness ECM connector 2 heated oxygen sensor adjustment current pin and the engine harness heated oxygen sensor connector adjustment current pin.
  • Measure the resistance between the engine harness ECM connector 2 heated oxygen sensor SIGNAL pin and the engine harness heated oxygen sensor connector SIGNAL pin.
  • Measure the resistance between the engine harness ECM connector 2 heated oxygen sensor reference RETURN pin and the engine harness heated oxygen sensor connector reference RETURN pin.

Refer to the circuit diagram or wiring diagram for connector pin identification.

For general resistance measurement techniques, refer to Resistance Measurements Using a Multimeter and Wiring Diagram, Procedure 019-360

Less than 10 ohms?
YES NO
No Repair

An open adjustment current signal or reference return circuit has been detected in the engine harness.

Repair the damaged pins. Replace the engine harness, whichever has the damaged pins.

  • Flush the dirt, debris, or moisture from the connector pins using electronic contact cleaner, Part Number 3824510.
  • Repair the engine harness. Refer to Procedure 019-204.
  • Replace the engine harness. Refer to Procedure 019-043.

Guided Step 4E – Check for a pin short to ground in the engine harness.

Conditions

  • Turn keyswitch OFF
  • Disconnect the engine harness connector 2 from the ECM
  • Disconnect the heated oxygen sensor from the engine harness.

Action

Check for an open circuit.

  • Measure the resistance between the engine harness ECM connector 2 heated oxygen sensor adjustment current pin and the engine block ground.
  • Measure the resistance between the engine harness ECM connector 2 heated oxygen sensor SIGNAL pin and the engine block ground.

Refer to the circuit diagram or wiring diagram for connector pin identification.

For general resistance measurement techniques, refer to Resistance Measurements Using a Multimeter and Wiring Diagram, Procedure 019-360

Less than 10 ohms?
YES NO
No Repair

A pin short to ground in the adjustment current or signal circuit has been detected in the engine harness.

Repair the damaged pins. Replace the engine harness, whichever has the damaged pins.

  • Flush the dirt, debris, or moisture from the connector pins using electronic contact cleaner, Part Number 3824510.
  • Repair the engine harness. Refer to Procedure 019-204.
  • Replace the engine harness. Refer to Procedure 019-043.

Guided Step 4F – Check for a pin to pin short circuit in the engine harness.

Conditions

  • Turn keyswitch OFF
  • Disconnect the engine harness connector 1 and connector 2 from the ECM
  • Disconnect the heated oxygen sensor from the engine harness.

Action

Check for a pin to pin short.

  • Measure the resistance between the heated oxygen sensor adjustment current pin in the engine harness ECM connector 2 and all other pins in the engine harness connector 2.
  • Measure the resistance between the heated oxygen sensor adjustment current pin in the engine harness ECM connector 2 and all other pins in the engine harness connector 1.
  • Measure the resistance between the heated oxygen sensor SIGNAL pin in the engine harness ECM connector 2 and all other pins in the engine harness connector 2.
  • Measure the resistance between the heated oxygen sensor SIGNAL pin in the engine harness ECM connector 2 and all other pins in the engine harness connector 1.

Refer to the circuit diagram or wiring diagram for connector pin identification.

For general resistance measurement techniques, refer to Resistance Measurements Using a Multimeter and Wiring Diagram, Procedure 019-360

Greater than 100k ohms?
YES NO
No Repair

A pin to pin short circuit on the signal line or adjustment current line has been detected in the engine harness.

Repair the damaged pins. Replace the engine harness, whichever has the damaged pins.

  • Flush the dirt, debris, or moisture from the connector pins using electronic contact cleaner, Part Number 3824510.
  • Repair the engine harness. Refer to Procedure 019-204.
  • Replace the engine harness. Refer to Procedure 019-043.

Guided Step 4G – Verify oxygen sensor operation.

Conditions

  • Connect all components.
  • Start and idle engine for 3 minutes.
  • Stop engine.
  • Turn keyswitch ON.
  • Connect INSITE™ electronic service tool.

Action

Perform the heated oxygen sensor test using the INSITE™ electronic service tool.

  • Use INSITE™ electronic service tool to activate the heated oxygen sensor test. Follow the directions given by the INSITE™ electronic service tool.

Did the sensor pass the test?
YES NO
No Repair

Replace the heated oxygen sensor. Refer to Procedure 019-100.

Use INSITE™ electronic service tool to reset the fuel tables.

Guided Step 5 – Clear the fault codes.

Guided Step 5A – Disable the fault code.

Conditions

  • Connect all components
  • Turn keyswitch ON
  • Connect INSITE™ electronic service tool.

Action

Disable the fault code.

  • Start the engine and let it idle for one minute.
  • Use INSITE™ electronic service tool to verify that Fault Code 752 is inactive.

Fault Code 752 inactive?
YES NO
No Repair

Return to troubleshooting steps or contact a local Cummins® authorized repair location if all steps have been completed and checked again.

Guided Step 5B – Clear the inactive fault codes.

Conditions

  • Connect all components
  • Turn keyswitch ON
  • Connect INSITE™ electronic service tool.

Action

Clear the inactive fault codes.

  • Use INSITE™ electronic service tool to erase the inactive fault codes.

All fault codes cleared?
YES NO
No Repair

Troubleshoot any remaining active fault codes.
Repair complete
Appropriate troubleshooting charts
Last Modified:  12-May-2005
Avatar photo

Published by Jack

Hello, I'm Jack, a diesel engine fan and a blogger. I write about how to fix and improve diesel engines, from cars to trucks to generators. I also review the newest models and innovations in the diesel market. If you are interested in learning more about diesel engines, check out my blog and leave your feedback.