Fix P0159: Mechanic’s solutions that WORKED

The code P0159: O2 Sensor Circuit Slow Response (Bank 2, Sensor 2) indicates a problem with the response time of the oxygen sensor located in Bank 2, Sensor 2. This sensor is responsible for monitoring the oxygen levels in the exhaust gases after they pass through the catalytic converter. A slow response from this sensor can lead to suboptimal engine performance and increased emissions.

P0159 quick overview

Meaning	P0159: O2 Sensor Circuit Slow Response (Bank 2, Sensor 2)
Is it serious?	Yes, it can affect the vehicle’s fuel efficiency, emissions, and overall performance.
Possible causes	– Faulty or aging O2 sensor – Exhaust leaks near the O2 sensor – Damaged or corroded wiring/connectors – Contaminated or failed catalytic converter – Engine misfires – Incorrect fuel pressure – Vacuum leaks – Use of incorrect or low-quality fuel
How to diagnose?	Inspect the O2 sensor for any visible damage or contamination. Check the wiring and connectors leading to the O2 sensor for any signs of damage or corrosion. Test the O2 sensor’s response with a scan tool or oscilloscope to ensure it’s functioning within the expected parameters. Examine the exhaust system for any leaks that could be affecting the O2 sensor’s readings. Evaluate the fuel system to ensure proper fuel pressure and no leaks. Check for engine misfires or any other running conditions that could lead to improper combustion. Inspect the catalytic converter to ensure it’s not contaminated or failing, as this can affect the O2 sensor’s readings.

In simpler terms, the P0159 code means that the oxygen sensor on the second bank of the engine, which checks the exhaust after it’s been treated by the catalytic converter, isn’t reacting as quickly as it should. This could mean the sensor is getting old or there’s a problem somewhere in the exhaust or fuel system. It’s important to get this checked out because it can lead to your car using more fuel and polluting more.

How to fix P0159 – learn from mechanics

I looked into P0159 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: Ram

Vehicle Information 2011 Ram 1500 ST, 3.7L engine

Issue + Repair History

• MIL (Malfunction Indicator Lamp) on
• Codes P0139 and P0159
• Both sensors replaced twice with Mopar parts
• No exhaust leaks detected
• ECM (Engine Control Module) replaced and updated
• Catalytic converters tested good at 94%
• All monitors pass
• Vehicle returned after 8000 miles with both codes

What Are People Suggesting to Fix Issue

• Check Technical Service Bulletins (TSBs) for updates or ECM problems
• Perform a smoke test from the tailpipe to check for exhaust leaks
• Apply pressure and soap solution to check for leaks at welded joints, O2 sensor seals, and flange connections
• Check wiring for shorts, opens, or voltage issues
• Consider replacing both upstream sensors as they might be slightly lazy and affecting downstream sensor performance

What Was the Final Fix Ran a smoke test and found no leaks. Ran new wiring from PCM to sensors and the issue was resolved.

Case #2: Nissan

Vehicle Information 2002 Nissan Maxima GXE, 3.5L engine

Issue + Repair History

• MIL (Malfunction Indicator Lamp) on
• Codes P0159 and P1167
• Issue persists after 700 miles

Other OBD2 Codes + Test Results

• Manifold Vacuum Readings: Idle at 18 in.

What Are People Suggesting to Fix Issue

• Replace the affected O2 sensor
• Check the sensor circuit and for exhaust leaks
• Consider replacing both catalytic converters

What Was the Final Fix The technician decided to pass on the job after learning that the Nissan dealer recommended replacing only one sensor without reprogramming the ECM, contrary to the TSB.

Case #3: Audi

Vehicle Information 2000 Audi A6 Quattro, 4.2L engine

Issue + Repair History

• MIL (Malfunction Indicator Lamp) on
• Multiple codes including secondary injection codes and O2 sensor bank 2 sensor 2 slow response
• Previous shop replaced air pump and both post O2 sensors

What Are People Suggesting to Fix Issue

• Check for water damage to ECM and corroded plugs
• Verify proper installation and function of O2 sensors
• Check for exhaust leaks and proper operation of secondary air system
• Consider replacing the airflow meter
• Inspect catalytic converters for degradation

What Was the Final Fix The O2 sensors were not installed in their correct locations; they were swapped. After correcting the placement, the issue was resolved.

Case #4: Alfa Romeo

Vehicle Information 2004 Alfa Romeo 156 JTS Sele, 2.0L engine

Issue + Repair History

• Poor idle quality, MIL (Malfunction Indicator Lamp) on
• Cleaned contacts for Lambda (O2) sensors 1 and 2, problem recurred after 2 weeks
• Replaced Lambda sensor 1, problem returned after 1 week

What Are People Suggesting to Fix Issue

• Check the air flow meter signal, fuel injection, and ignition energy flow
• Scope the O2 sensor to see if it’s cycling and create a misfire to test sensor response
• Check for induction leak or mass airflow fault
• Provide more detailed information for better diagnostic assistance

What Was the Final Fix The upstream Lambda sensors’ connections were known to be problematic. Both connectors were fixed by removing each pin, re-soldering, and cleaning. After testing, the Check Engine Light did not return.

Case #5: Volkswagen

Vehicle Information 2001 Volkswagen Cabrio GLX, 2.0L engine

Issue + Repair History

• MIL (Malfunction Indicator Lamp) on with code P0133
• Initially replaced the mass air flow sensor due to failure, cleared codes
• Car returned with P0133 code
• Downstream O2 sensor showed no activity on the scanner, but tested fine with a lab scope
• Wiring checked and found to be fine
• Tested O2 wire at the ECM with the lab scope and found similar readings as at the sensor

What Are People Suggesting to Fix Issue

• Replace the O2 sensor without relying solely on scope-checking
• Unplug the O2 sensor while monitoring the scanner to check if the scanner is marking the data correctly
• Check for a TSB (Technical Service Bulletin) that advises not to replace the ECM for certain fault codes
• Consider that the downstream sensor might be gummed up or bad and may need replacement

What Was the Final Fix The downstream O2 sensor was giving a swing voltage from about 100mv to 900mv cold, which was misleading because the scope was set on 1 volt. Upon adjusting the scope to a higher scale, it was found that the sensor was switching from 5 volts to less than 1 volt, indicating that the sensor was far out of range. The computer likely defaulted to a fail-safe value of 425mv on the scanner. Replacing the downstream O2 sensor resolved the issue.

Advice	Brief Description of Diagnostic Step
Replace the O2 Sensor	If the O2 sensor is showing erratic behavior or no activity, replacing it is often the first and most common step.
Check Wiring and Connectors	Ensure that the wiring and connectors to the O2 sensor are intact and not corroded. Poor connections can cause false readings.
Use a Lab Scope	A lab scope can provide a more accurate reading of the O2 sensor’s performance compared to some scan tools.
Don’t Rely Solely on Scan Tool Readings	Scan tools can sometimes provide misleading information. Double-check with direct testing methods like a lab scope.
Check for Exhaust Leaks	An exhaust leak upstream of the O2 sensor can cause false readings and trigger the fault code.
Consider ECM/PCM Issues Last	ECM/PCM failures are rare. Exhaust all other diagnostic steps before considering ECM/PCM replacement.
Consult TSBs (Technical Service Bulletins)	TSBs can provide model-specific advice and common fixes for known issues.
Check Fuel Trims	Fuel trims can provide insights into whether the issue is with the O2 sensor or another part of the fuel system.
Verify Correct Sensor Placement	Ensure that the O2 sensors are installed in their correct locations, as swapping them can cause issues.
Test Sensor Operation	Create conditions (like inducing a misfire) to test if the O2 sensor responds appropriately.
Check Sensor Type	Ensure the correct type of sensor is used (e.g., wideband vs. narrowband), as they have different operating ranges.
Replace with OEM Parts	Using original equipment manufacturer (OEM) parts can prevent compatibility issues that may arise with aftermarket parts.