DTC P0138. Saturn ION 2005

For 1990-2009 cars only

Makes 🢒 Saturn 🢒 2005 🢒 ION 🢒 Restraints 🢒 SIR 🢒 DTC P0138

Circuit Description

Heated oxygen sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content in the exhaust stream. The HO2S must reach operating temperature to provide an accurate voltage signal. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature. The engine control module (ECM) supplies the HO2S with a reference, or bias, voltage of about 450 mV. When the engine is first started the ECM operates in Open Loop, ignoring the HO2S voltage signal. Once the HO2S reaches operating temperature and Closed Loop is achieved, the HO2S generates a voltage within a range of 0-1,000 mV that fluctuates above and below bias voltage. High HO2S voltage indicates a rich exhaust stream, and low HO2S voltage indicates a lean exhaust stream. If the ECM detects that HO2S 2 voltage stays above a specified value, DTC P0138 will set.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0138 HO2S Circuit High Voltage Sensor 2

Conditions for Running the DTC

•	DTCs P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0171, P0172, P0300, P0336, P0340, P0341, P0455, P0500, P0601, P0602, P0606, P0641, P0722, P0723 are not set.

•	The Loop Status parameter is closed.

•	The Air Fuel Ratio parameter is between 14.5:1 and 14.8:1.

•	The transmission is in Drive with automatic transmission.

•	DTC P0138 runs continuously when the above conditions are met.

Conditions For Setting The DTC

Rich Test

•	The ECM detects that the HO2S 2 voltage parameter is more than 1,065 mV.

•	DTC P0138 sets during the rich test within 100 seconds when the above condition is met.

Decel Fuel Cutoff Test

•	The ECM detects that the HO2S 2 voltage parameter is more than 587 mV.

•	DTC P0138 sets during the decel fuel cutoff test within 10 seconds when the above condition is met.

Action Taken When the DTC Sets

•	The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.

•

The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

Conditions for Clearing the MIL/DTC

•	The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.

•	A current DTC, Last Test Failed, clears when the diagnostic runs and passes.

•	A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.

•	Clear the MIL and the DTC with a scan tool.

Test Description

The number below refers to the step number on the diagnostic table.

If the voltage is more than the specified value, the condition is present.

Step

Action

Values

Yes

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Engine Controls Connector End Views or Engine Control Module Connector End Views

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

Start the engine.
Allow the engine to reach operating temperature. Refer to Scan Tool Data List .
Operate the engine at 1,500 RPM for 30 seconds.
Observe the HO2S 2 voltage parameter with a scan tool.

Is the HO2S 2 voltage parameter more than the specified value?

1,065 mV

Go to Step 4

Go to Step 3

Observe the Freeze Frame/Failure Records for this DTC.
Turn OFF the ignition for 30 seconds.
Start the engine.
Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

Go to Step 4

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

Turn OFF the ignition.
Disconnect the heated oxygen sensor (HO2S) 2.
Turn ON the ignition, with the engine OFF.
Observe the HO2S 2 voltage parameter with a scan tool.

Is the HO2S 2 voltage parameter within the specified range?

400-500 mV

Go to Step 5

Go to Step 6

Connect a 3-amp fused jumper wire between the high signal circuit of the HO2S 2 harness connector on the vehicle harness side and the low signal circuit of the HO2S 2 harness connector on the vehicle harness side.
Observe the HO2S 2 voltage parameter with a scan tool.

Is the HO2S 2 voltage parameter more than the specified value?

800 mV

Go to Step 8

Go to Step 7

Important: The sensor may be damaged if the circuit is shorted to a voltage source.

Test the HO2S 2 high signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 15

Go to Step 14

Is the HO2S 2 voltage parameter less than the specified value?

10 mV

Go to Step 10

Go to Step 8

Important: The engine control module (ECM) may be damaged if the heated oxygen sensor (HO2S) low signal circuit is shorted to a voltage source.

Test the HO2S 2 low signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 15

Go to Step 9

Test the HO2S 2 low circuit for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 15

Go to Step 12

The HO2S 2 may be detecting a rich exhaust condition or may be contaminated. Inspect for the following conditions:

Notice: Refer to Silicon Contamination of Heated Oxygen Sensors Notice in the Preface section.

•	A silicon contaminated HO2S 2

•	Any water intrusion into the HO2S 2 connector

•	Engine oil contaminated with fuel

•	An EVAP canister purge condition

•	An incorrect fuel pressure--Refer to Fuel System Diagnosis .

•	Any rich fuel injectors--Refer to Fuel Injector Balance Test with Special Tool .

•	A leaking fuel pressure regulator--Refer to Fuel System Diagnosis .

•	An inaccurate manifold absolute pressure (MAP) sensor--Refer to Scan Tool Data List .

•	An air intake restriction or collapsed air intake duct

Repair any of the above or similar engine conditions as necessary.

Did you find and correct the condition?

Go to Step 15

Go to Step 11

Test the for an intermittent and for a poor connection at the HO2S 2. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 15

Go to Step 13

Test for an intermittent and for a poor connection at the ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 15

Go to Step 14

Replace the HO2S 2. Refer to Heated Oxygen Sensor 2 Replacement .

Did you complete the replacement?

Go to Step 15

Replace the ECM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 15

Clear the DTCs with a scan tool.
Turn OFF the ignition for 30 seconds.
Start the engine.
Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

Go to Step 2

Go to Step 16

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information

System OK