Fix P0161: Mechanic’s solutions that WORKED

The code P0161: Heated Oxygen Sensor Heater Performance Bank 2 Sensor 2 points out a fault in the oxygen sensor’s heater circuit, and most likely is caused by a malfunctioning oxygen sensor, wiring issues, or a faulty PCM.

P0161 quick overview

Meaning	P0161: Heated Oxygen Sensor Heater Performance Bank 2 Sensor 2
Is it serious?	Moderately serious. While the vehicle may still run, it might not run efficiently, and fuel consumption can increase. Prolonged driving with this issue can lead to damage to the catalytic converter and increased emissions.
Possible causes	– Faulty oxygen sensor – Damaged or corroded wiring or connectors – Oil or other contaminants in the sensor connector – Faulty PCM or need for PCM update – Harness chaffing or misrouting
How to diagnose?	Visual Inspection: Check the oxygen sensor and its wiring for visible damage or oil contamination. Check for Technical Service Bulletins (TSBs): Manufacturers might have released information about known issues and solutions for this code. Test the Oxygen Sensor: Use a multimeter to check the sensor’s readings. If it’s not within the manufacturer’s specifications, it might need replacement. Inspect Wiring and Connectors: Look for signs of damage, corrosion, or oil contamination. Clean or replace as necessary. Check the PCM: Inspect the Powertrain Control Module for faults. Consider reprogramming or updating the software if needed. Harness Inspection: Examine the harness for signs of chaffing or misrouting, especially near the O2 sensors.
What is Bank2 Sensor 2?	Downstream oxygen sensor for engine head 2. Read the full Bank1 vs Bank2 explanation.

How to fix P0161 – learn from mechanics

I looked into P0161 service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.

Case #1: Jeep

2012 Jeep Compass Limited 2.4L Transmission

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Vehicle Information:

• 2012 Jeep Compass Limited, 2.4L engine

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Issue + Repair History:

• Vehicle intermittently failed to start.
• Loss of power while driving; had to turn off and restart to temporarily resolve.
• Mileage: 82,356
• Code registered: P0161B (later corrected to P161B) – BATTERY DISCONNECT/TCM INTERNAL.
• Previous repairs: None mentioned.

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Other Codes + Test Results:

• Gasoline pressure: Ok
• Battery voltage while running: 14.3 volts
• Battery voltage while starting: 11.2 volts

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Community Suggestions:

• Verify all powers and grounds to the TCM.
• Consider the possibility of an incorrect TCM being installed.
• Use a different scan tool to confirm the fault code.
• Check TCM connectors for corrosion or loose clips.
• Wiggle test the harness to see if it affects the issue.
• If wiring and grounds to the TCM are fine, consider an internal TCM issue.

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Final Fix:

• The vehicle was left overnight with the battery disconnected.
• The next day, the code was gone, and the vehicle functioned normally.
• No specific repair procedure was charged to the customer, but the recommendation was to monitor and return if the problem reoccurred. The issue did not return.

Case #2: Ford

Vehicle Information:

• 1996 Ford Explorer Eddie Bauer, 5.0L engine

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Issue + Repair History:

• MIL lamp on.
• All four O2 heaters show a code.
• Fuse #24 in dash fuse box had no power; it should have had a 20 amp fuse but had a 10 amp.
• Power for this fuse comes from PCM power relay in power distribution box.
• Relay was good, but there was an open circuit from the relay to the fuse box.
• Previous repairs: None mentioned.

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Other Codes + Test Results:

• P0135– O2 1 BANK # 1 Heater Circuit Malfubction
• PO141 – O2 2 BANK # 1 ” ” ”
• PO155 – O2 1 BANK # 2 Heater Circuit Malfunction
• PO161 – O2 2 BANK # 2 ” ” “

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Community Suggestions:

• Consider an overlay before dismantling.
• Check for water leaks in the cowl that might affect the fuse panel.
• Check if the O2 sensor had shorted a fuse.
• The required fuse is in the power distribution box under the hood, not in the dash.
• Check the PCM as a potential issue.

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Final Fix:

• The correct fuse was identified in the power distribution box.
• After replacing the fuse, the system worked for about a day before the fuse blew again.
• The left bank O2 sensor was replaced, and the issue was resolved.

Case #3: Chevrolet

Vehicle Information:

• 1996 Chevrolet Caprice Classic, 5.7L engine

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Issue + Repair History:

• MIL light on.
• Code P0161 stored indicating oxygen sensor heater circuit failure.
• Uncertainty about which of the 4 O2 sensors had the faulty circuit.
• Replaced bank 2 sensor 2 (rear sensor, right side) but the light came back on.
• All 4 positions use the same part numbered O2 sensor.

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Other Codes + Test Results:

• Code registered: P0161 – Oxygen sensor heater circuit failure.

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Community Suggestions:

• Check the circuit using a multimeter and backprobe pins.
• Use an AC Delco sensor for replacement.
• Check the power and ground circuits to the O2 sensor.
• Consider replacing all O2 sensors.
• Use a scan tool with live data to identify the faulty sensor.
• Check circuit 439 for 12v with KOEO.
• Check the draw on the heater circuit with an amp clamp.
• Consider moving sensors to different locations in the exhaust to see if the code changes.

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Final Fix:

• The issue was with the right rear oxygen sensor heater.
• The power feed to the sensor had pushed back out of the connector on the harness side when plugged in, causing no power to the oxygen sensor heater.

Case #4: BMW

Vehicle Information:

• 2002 BMW X5 3.0i, 3.0L engine

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Issue + Repair History:

• MIL light on.
• Multiple codes found in various modules due to lack of servicing and weak battery.
• Two codes in *DME:
  • BF Insufficient heat output oxygen sensor behind Cat bank 2.
  • Evap leak.
• Evap test (GT1) passed.
• Performed necessary service and replaced battery.
• Cleared all codes and took an extended road test. All monitors set except for evap and Cat monitoring.
• P0161 code stored again, even though MIL is off.
• Resistance of oxygen sensor heaters checked and found to be 3 ohms. Both post-cat sensors had power and ground to the heaters.
• Uncertainty about whether to replace the oxygen sensor or look for another underlying cause.

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Other Codes + Test Results:

• Code registered: P0161 – Insufficient heat output oxygen sensor bank2 behind cat.

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Community Suggestions:

• Consider reprogramming the DME as there’s a T.S.B for O2 sensor codes including heater circuit malfunctions.
• Check the DME software update, especially if it addresses O2 sensor codes.
• Ensure the power supply and ground are okay, then check the connector. If not resolved, consider replacing the DME.
• Update the DME using version 38 or higher of DIS as per service information.

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Final Fix:

• The issue was addressed by a software update to the DME as per a TSB that covered various O2 sensor codes.
• After updating the DME and an extended road test, all monitors set and no codes were stored.

*DME stands for “Digital Motor Electronics.” In the context of BMW vehicles, the DME is the primary computer control module responsible for the management and control of the engine.

Case #5: Cadillac

Vehicle Information

• 2003 Cadillac CTS, 3.2L engine

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Issue + Repair History

• MIL (Malfunction Indicator Lamp) on
• Fault codes: PO160 (heated o2 sensor insufficient activity bank 2) and P0161 (heated 02 sensor heater performance bank 2 sensor 2)
• Sensor consistently reading 5,000 milivolts
• Severe oil leak from driver’s side valve cover, dripping onto the harness and connector for B2S2
• New O2 sensor installed; occasionally pegged 2,000 or 5,000 milivolts
• Valve cover gaskets replaced due to oil leak
• Misfire data showed misfires on cylinders 1,3, and 5
• Suspected PCM failure

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Other OBD2 Codes + Test Results

• No other codes mentioned

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Suggestions from Community

1. PCM failures in these cars are common
2. Check the iATN Fix Database for similar issues
3. GM had issues with harness chaffing on O2 sensor 2 Bank 2; inspect before condemning PCM

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Final Fix

• The PCM was the issue. A used PCM was installed, but due to communication issues, it wouldn’t start the vehicle. The old PCM was reinstalled and reprogrammed by a local Cadillac dealer.