DTC P0139 or P0159. Cadillac STS 2005

For 1990-2009 cars only

Makes 🢒 Cadillac 🢒 2005 🢒 STS 🢒 Engine 🢒 Engine Controls - 4.6L (LH2) 🢒 DTC P0139 or P0159

Circuit Description

The heated oxygen sensor (HO2S) produces a voltage that varies between 100-900 mV under normal operating conditions. The engine control module (ECM) produces a bias voltage on the HO2S signal circuit of 420-480 mV. The reference ground for the sensor is provided through the ECM. The ECM monitors the signal voltage to determine if the exhaust is lean or rich. The oxygen sensor voltage is high when the exhaust is rich, and low when the exhaust is lean. The ECM constantly monitors the HO2S signal during the Closed Loop operation. If the ECM detects that the decel fuel cut-off rich-to-lean transition time is too long, DTC P0139 will set for bank 1 sensor 2, or DTC P0159 will set for bank 2 sensor 2.

DTC Descriptors

This diagnostic procedure supports the following DTCs:

•	DTC P0139 HO2S Slow Response Bank 1 Sensor 2

•	DTC P0159 HO2S Slow Response Bank 2 Sensor 2

Conditions for Running the DTC

•

DTCs P0021, P0024, P0030, P0031, P0032, P0036, P0037, P0038, P0050, P0051, P0052, P0056, P0057, P0058, P0101, P0102, P0103, P0106, P0107, P0108, P0116, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0131, P0132, P0135, P0137, P0138, P0139, P0140, P0141, P0151, P0152, P0155, P0157, P0158, P0159, P0160, P0161, P0201-P0208, P0221, P0222, P0223, P0261, P0262, P0264, P0265, P0267, P0268, P0270, P0271, P0273, P0274, P0276, P0277, P0279, P0280, P0282, P0283, P0300, P0301-P0308, P0335, P0336, P0340, P0341, P0345, P0346, P0351-P0358, P0365, P0366, P0390, P0391, P0442, P0443, P0446, P0449, P0453, P0454, P0455, P0458, P0459, and P0496 are not set.

•	The ECT Sensor parameter is more than 66°C (151°F).

•	The Vehicle Speed Sensor parameter is between 5-180 km/h (3-112 mph).

•	The calculated catalytic converter temperature is more than 520°C (968°F).

•	DTC P0139 or P0159 runs continuously once the above conditions are met.

Conditions for Setting the DTC

The ECM detects that the decel fuel cut-off and rich-to-lean transition time has exceeded 1 second.

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.

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

Allow the engine to reach normal operating temperature. Refer to Scan Tool Data List .
Quickly cycle the throttle from closed throttle to wide open throttle (WOT) 3 times within 5 seconds while observing the HO2S Bank 1 Sensor 2 or HO2S Bank 2 Sensor 2 voltage parameter with a scan tool.

Does the voltage react immediately when performing the above action?

Go to Step 3

Go to Step 4

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 Intermittent Conditions

Turn OFF the ignition.
Disconnect the affected heated oxygen sensor (HO2S) 2.
Connect a 3-amp fused jumper wire between the HO2S high signal circuit, on the engine harness side connector, and a good ground.
Turn ON the ignition, with the engine OFF.
Observe the affected HO2S 2 parameter with a scan tool.

Is the voltage less than the specified value?

25 mV

Go to Step 5

Go to Step 7

Remove the jumper wire from the previous step.
Connect a 3-amp fused jumper wire between the HO2S high signal circuit and the HO2S low signal circuit, on the engine harness side connector.
Observe the affected HO2S 2 parameter with a scan tool.

Is the voltage less than the specified value?

25 mV

Go to Step 6

Go to Step 8

Remove the jumper wire from the previous step.
Measure the resistance of the following circuits with a DMM:

•	The HO2S heater low control circuit

•	The ignition 1 voltage circuit

•	Refer to Circuit Testing in Wiring Systems.

Is the resistance of either circuit more than the specified value?

5 ohms

Go to Step 12

Go to Step 9

Test the HO2S high signal circuit for an open or high resistance. Refer to Circuit Testing , Wiring Repairs , and Heated Oxygen Sensor Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 15

Go to Step 11

Test the HO2S low signal circuit for an open or high resistance. Refer to Circuit Testing , Wiring Repairs , and Heated Oxygen Sensor Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 15

Go to Step 11

The HO2S is detecting a rich or lean exhaust condition or may be contaminated. Inspect for one of the following conditions:

•	HO2S connector water intrusion

•	A silicon-contaminated HO2S

•	Fuel-contaminated engine oil

•	Incorrect fuel pressure--Refer to Fuel System Diagnosis .

•	Rich fuel injectors

•	Lean fuel injectors--Refer to Fuel System Diagnosis .

•	An exhaust leak between the HO2S and the engine--Refer to Exhaust Leakage in Engine Exhaust.

•	Vacuum leaks

•

Fuel contamination--Water, even in small amounts, can be delivered to the fuel injectors. The water can cause a lean exhaust to be indicated. Excessive alcohol in the fuel can also cause this condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis for the proper procedure for inspecting for contaminants.

•	An inaccurate mass air flow (MAF) sensor

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 10

Test for intermittent and poor connections at the HO2S. Refer to Testing for Intermittent Conditions and Poor Connections , Connector Repairs , and Heated Oxygen Sensor Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 15

Go to Step 13

Test for intermittent and poor connections at the engine control module (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

Repair the circuit with high resistance. Refer to Wiring Repairs and Heated Oxygen Sensor Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 15

Replace the affected HO2S. Refer to Heated Oxygen Sensor Replacement - Bank 1 Sensor 2 or Heated Oxygen Sensor Replacement - Bank 2 Sensor 2 .

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