GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 Epica 🢒 DTC 🢒 DTC 044

Circuit Description

The electronic control module (ECM) supplies a voltage of about 450 millivolts between the ECM terminals D9 and C9. The oxygen sensor (O2S) varies the voltage within a range of about 1 volt if the exhaust is rich, down to about 100 millivolts if the exhaust is lean. The oxygen sensor is like an open circuit and produces no voltage when it is below 360°C (600°F). An open oxygen sensor circuit or a cold oxygen sensor causes Open Loop operation.

Conditions for Setting the DTC
    • The engine controls system is in Closed Loop.
    • The oxygen sensor voltage is below 274 millivolts.
    • The engine has been running for at least 60 seconds.
    • DTCs 021, 022, 033, and 034 has not set.
    • The throttle angle is above 5 percent.
    • The engine coolant temperature (ECT) is above 70°C (158°F).
    • These conditions are present for at least 40 seconds.

Diagnostic Aids
    • Normal scan tool voltage varies between 100-999 millivolts while in Closed Loop.
    • Inspect the oxygen sensor wire. The oxygen sensor pigtail may be positioned incorrectly and contacting the exhaust manifold.
    • Inspect for an intermittent ground in the wire between the oxygen sensor and the ECM.
    • Perform an injector balance test to determine if a restricted fuel injector may be causing the lean running condition.
    • Vacuum or crankcase leaks will cause a lean running condition.
    • An exhaust manifold gasket leak or a cracked exhaust manifold may cause outside air to be pulled into the exhaust and past the sensor.

Step

Action

Values

Yes

No

1

Was the Diagnostic System Check performed?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2
  1. Connect the scan tool to the data link connector (DLC).
  2. Run the engine until it reaches operating temperature.
  3. Run the engine at 1,200 RPM.

Does the scan tool read the oxygen sensor (O2S) voltage fixed below the value specified?

274 mV

Go to Step 3

Go to Diagnostic Aids

3
  1. Disconnect the O2S connector.
  2. Run the warm engine at idle.

Does the scan tool read O2S voltage within the value specified?

350-550 mv

Go to Diagnostic Aids

Go to Step 4

4
  1. Turn the ignition to LOCK.
  2. Inspect the O2S signal wire between the O2S and engine control module (ECM) connector terminal D9 for a short to ground.

Is the problem found?

--

Go to Step 5

Go to Step 6

5
  1. Repair the wire or the connector terminal as needed.
  2. Clear any DTCs from the ECM.
  3. Road test the vehicle.
  4. Perform the Diagnostic System Check.

Is the repair complete?

--

System OK

--

6
  1. Replace the ECM. Refer to Engine Control Module Replacement .
  2. Road test the vehicle.
  3. Perform the Diagnostic System Check.

Is the repair complete?

--

System OK

--