Fix P0150: Mechanic’s solutions that WORKED

The code P0150: O2 Sensor Circuit Malfunction (Bank 2, Sensor 1) points out a fault in the oxygen sensor located on Bank 2, Sensor 1 of the engine. This issue is most likely caused by a malfunctioning O2 sensor, wiring issues, or problems with the vehicle’s computer.

P0150 quick overview

Meaning	P0150: O2 Sensor Circuit Malfunction (Bank 2, Sensor 1)
Is it serious?	Yes, it can affect fuel efficiency, engine performance, and emissions.
Possible causes	– Faulty O2 sensor – Wiring or connector issues related to the O2 sensor – Vacuum leaks – Faulty computer (ECM/PCM) – Grounding issues – Incorrect O2 sensor type installed
How to diagnose?	Scan the vehicle with an OBD2 scanner to confirm the P0150 code and check for any other related codes. Visually inspect the wiring and connectors related to the O2 sensor for damages or disconnections. Test the O2 sensor’s voltage readings using a multimeter or lab scope. Compare the readings to manufacturer specifications. Check for vacuum leaks in the engine, as they can affect O2 sensor readings. Inspect the ground connections, especially if there’s a known issue with grounding in the specific vehicle model. Verify that the correct type of O2 sensor is installed, especially if it has been recently replaced. If all else fails, consider the possibility of a faulty computer (ECM/PCM) and seek professional diagnosis.
What is Bank 2 sensor 1?	Oxygen sensor before catalytic converter on engine head 2. Read the full Bank1 vs Bank2 explanation here.

How to fix P0150 – learn from mechanics

I looked into P0150 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: Mercedes

Vehicle Information:

• 1999 Mercedes-Benz S420, 4.2L Engine

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Issue + Repair History:

• MIL (Malfunction Indicator Lamp) is on.
• Fault codes: p0150, p0151, p0130, p0131 (all related to O2 sensors).
• Through data stream, all O2 sensors appear operational.
• O2 sensors look recently replaced.
• Vehicle feels slightly rough on idle.
• Technician wonders if a vacuum leak or poor fuel consumption from worn spark plugs could be causing the codes.

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Suggestions from the Community:

• The code specifically applies to the Left Front sensor (before the catalytic converter). It’s essential when the sensor value remains either above 1.5v or below 0.15 volts.
• Verify the sensor heater’s functionality as many sensors might not maintain adequate heat without a working heater.
• Inquire about who replaced the sensors and if the codes were cleared post-replacement.
• Check if the O2 sensors are from Bosch, as some brands might not function as effectively.
• Consider checking adaptations with a scan tool.
• Use Star Diagnostic to run all monitors without driving.

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Final Fix:

• Found vacuum leaks from the breather system.
• Replaced worn spark plugs.
• Noted an initial rotten egg smell indicating unburned fuel, which cleared after letting the car idle for about ten minutes.
• The previously installed spark plugs were not suitable for the vehicle, potentially causing improper fuel burning.

Case #2: Land Rover

Vehicle Information:

• 1996 Land Rover Discovery SD, 4.0L Engine

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Issue + Repair History:

• MIL (Malfunction Indicator Lamp) is on.
• Fault codes: PO130 & PO150.
• 6 months prior, bank 1 sensor 1 was replaced due to code PO130.
• MAF (Mass Air Flow) sensor was cleaned.
• Vacuum readings: Idle at 15 & cruise at 18.
• Previous repairs: Bank 1 sensor 1 replacement, tune-up, gas filter change, MAF sensor cleaning.

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Suggestions from the Community:

• Check for a vacuum leak or exhaust leak on the left side of the engine.
• Ensure connections at each O2 sensor are clean and tight.
• Check the operation of the O2 sensor heaters and contacts at the ECM (Engine Control Module).
• Consider replacing a PROM set in the ECM if the sensors operate correctly.
• Look for vacuum leaks or leaking injectors affecting one side of the engine.
• Consider switching the front O2 sensors to see if the code follows.

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Final Fix:

• Local dealer replaced the PROM, charging $426.00.
  
  (PROM is a computer chip in cars that stores specific software. Once this software is put on the PROM, it can’t be changed. If there’s an issue with the car’s software, the PROM might be replaced to fix it.)

Case #3: Ford

2010 Ford F-150 STX 4.6L MIL Lamp on

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Vehicle Information:

• 2010 Ford F-150 STX
• Engine: 4.6L

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Issue + Repair History:

• MIL lamp on with code po150 b2s1 o2.
• Circuit tested good, so O2 sensor was replaced.
• Truck returned with the same code.
• Wiring checked again and found to be good.
• Different sensor tried, but the problem persisted.
• Sensor not switching at all.
• Ford refers to it as a universal O2 sensor.

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Community Suggestions:

1. Ensure the correct O2 sensor was received as there are different ones for vin”8″ and vin”W”.
2. The sensor is an air-fuel ratio sensor, not a traditional O2 sensor. Check fuel trims and FF data. Vacuum leaks and other issues can affect the sensor.
3. Use only OEM sensor due to precise calibration.
4. Check if an aftermarket sensor was used as they might not be as effective as OEM.
5. Ford might have shifted to A/F sensors like other manufacturers. These sensors measure amps and have a fast switch rate. Issues might be in the heater circuit.

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Final Fix:

• While checking the harness, the code changed from po150 to po155 b2s1 indicating a heater problem.
• The connector at the end of the harness where the sensor plugs in was identified as the issue.
• Ford’s repair connector part # is wpt-1145 or bu2z-14s411-na was used to address the problem.

Case #4: Infiniti

1996 Infiniti I30 3.0L MIL Lamp on

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Vehicle Information:

• 1996 Infiniti I30
• Engine: 3.0L

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Issue + Repair History:

• MIL light on.
• Scanner showed code P0150.
• O2 sensors checked with lab scope and appeared fine, not matching scanner readings.
• Even after disconnecting O2 sensors, a reading of 1500 mv was observed when throttle was snapped.
• Scanner indicated one of the O2 sensor heaters was off and the egrc solenoid was on.
• Uncertainty about whether the issue was with the scanner or the car’s wiring/harness.

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Community Suggestions:

• Potential harness problem.
• Possible scanner issue.
• Doubt about O2 sensors being the problem.

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Final Fix:

• Customer took the car to the dealer.
• All O2 sensors were replaced by the dealer at no cost.

Case #5: Nissan

1996 Nissan Pathfinder LE 3.3L MIL Lamp on

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Vehicle Information:

• 1996 Nissan Pathfinder LE
• Engine: 3.3L

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Issue + Repair History:

• MIL light on.
• Initial code was PO130 (circuit malfunction bank one sensor 1). No driveability problems.
• After visual checks and code clearance, codes PO130 and PO150 (circuit malfunction for bank 2 sensor 1) appeared.
• A TSB (NTB99-004) indicated a bad ground between intake and cylinder heads. Voltage drop tested high. Installed extra ground as per TSB, which corrected the voltage drop.
• Vehicle returned with MIL on and code PO130.
• Bank 1 Sensor 1 O2 sensor was replaced, but the issue persisted. Power and ground for the computer were checked.

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Community Suggestions:

• Test the O2 sensors by back probing the connectors and ensure 12v at the b/w wire.
• Check for vacuum leaks which can affect O2 readings.
• Use both Nissan and OBD2 connectors for testing and compare codes.

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Final Fix:

• A technician suggested comparing scanner codes from the OBD2 connector and the OEM factory connector. OBD2 showed P0130 and P0150, while the OEM connector showed only P0150.
• After already replacing the right side O2 sensor, the left side O2 sensor was replaced.
• No light appeared after over a week. The sensors were expensive, with the right side listed at $175.00 and the left side at $139.00.

Advice	Brief Description of Diagnostic Step
Check O2 Sensors	Before replacing, back probe the O2 sensor connectors to ensure they are functioning correctly.
Use OEM Sensors	Aftermarket sensors might not always be compatible or accurate. It’s recommended to use original equipment manufacturer (OEM) sensors.
Inspect Wiring and Connectors	Faulty connectors or wiring can cause the code. Ensure the harness and connectors are in good condition.
Check for Vacuum Leaks	Vacuum leaks can affect O2 readings and trigger the fault code.
Refer to Technical Service Bulletins (TSBs)	TSBs might provide information on known issues and fixes for specific vehicle models.
Use Multiple Diagnostic Tools	Compare readings from different connectors (e.g., OBD2 and OEM) to ensure accurate diagnosis.
Ensure Proper Grounding	Bad grounds can cause incorrect sensor readings. Check and improve grounding if necessary.