GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1998 🢒 GMC C-Series Medium Duty Truck C6/C7/C8 🢒 DTC 🢒 DTC 44 Lean Exhaust Indicated

Object Number: 339433 Size: SF
Engine Controls Components
Cell 20: Sensors
Handling ESD Sensitive Parts Notice

Circuit Description

The ECM supplies a voltage of about 0.45 volt between terminals D6 and D7. (If measured with a J 39200 , this may read as low as 0.32 volt.) The oxygen sensor varies the voltage within a range of about 1.0 volt if the O2S signal is rich, down through about 0.10 volt if O2S signal is lean.

The sensor is like an open circuit and produces no voltage when it is below about 315°C (600°F). An open sensor circuit or cold sensor causes Open Loop operation.

Conditions for Setting the DTC
    • O2S signal voltage remains below 0.2 volt.
    • System is operating in Closed Loop.
    • All conditions are met for 20 seconds.

Action Taken When the DTC Sets

The Malfunction Indicator Lamp (MIL) will illuminate. The system will go Open Loop.

Conditions for Clearing the MIL/DTC

The conditions for the fault are no longer present and 50 ignition cycles have passed with no further faults or the ignition switch is turned OFF and the battery feed voltage is removed for 10 seconds.

Diagnostic Aids
    • Using the scan tool, observe the long term fuel trim values at different RPM and air flow conditions. If the conditions for a DTC 44 exist, the long term fuel trim values will be around 150.
    • Oxygen sensor wire -- The sensor pigtail may be mis-positioned and contacting the exhaust manifold.
    • Check for an intermittent ground in the wire between the connector and the sensor.
    • Fuel contamination -- Water, even in small amounts near the in-tank fuel pump inlet, can be delivered to the injectors. The water causes a lean O2S signal and can set a DTC 44.
    • Fuel pressure -- System will be lean if the pressure is too low. Monitor fuel pressure while driving the vehicle at various road speeds and/or loads in order to confirm. Refer to Fuel System Diagnosis
    • If the O2S ground circuit is open, the voltage at terminal D7 will be over one volt.
    • If everything checks out OK, the oxygen sensor is faulty. Refer to Oxygen Sensor Replacement .

Test Description

The number below refers to the step number on the Diagnostic Table.

  1. This step checks to see if DTC was set as result of a hard failure or intermittent condition.

DTC 44 Lean Exhaust Indicated

Step

Action

Value(s)

Yes

No

1

Did you perform the On-Board Diagnostic (OBD) System Check?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

  1. Install a scan tool.
  2. Make sure the engine temperature is within the specified value.
  3. Run the engine speed at the specified value.

Does the scan tool display an oxygen sensor voltage fixed below the specified value?

75-95°C (167-203°F)

1,200 RPM

0.35 V

Go to Step 3

Go to Diagnostic Aids

3
  1. Disconnect the oxygen sensor (O2S) harness connector.
  2. Run the engine at idle.

Does the scan tool display a voltage within the specified value?

0.35-0.55 V (350-550 mV)

Go to Diagnostic Aids

Go to Step 4

4
  1. Check the oxygen sensor signal circuit for a short to ground.
  2. If you find a problem, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find a problem?

--

Go to Step 6

Go to Step 5

5

Replace the ECM. Refer to Engine Control Module Replacement

Is the action complete?

--

Go to Step 6

--

6
  1. Clear the DTCs. Refer to Clearing DTCs.
  2. Start the engine and allow the engine to idle at the normal operating temperature.
  3. Operate the vehicle within the conditions for setting this DTC as specified in the supporting text.

Did the DTC reset?

--

Go to Step 2

Go to Step 7

7

Are any DTCs stored which you have not diagnosed?

--

Go to the Applicable DTC Table

System OK