P046B7 – Swirl Flaps Adaptation (specific to some BMW models)

What is Code P046B?

OBD-II trouble code P046B is defined as "Catalyst Temperature Sensor 1/2 Correlation". This is a generic powertrain code that applies to many makes and models. It indicates a problem with the correlation between the upstream and downstream catalytic converter temperature sensors.

Issue Severity and Driving Considerations

Code P046B is considered a moderate severity trouble code. While it will not cause the vehicle to break down immediately, it can lead to improper functioning and potential overheating of the catalytic converter if left unaddressed.

When this code is present, you may notice reduced fuel efficiency but the vehicle should still be drivable in most cases. However, it's best to diagnose and repair the issue as soon as possible to prevent catalytic converter damage. If the catalytic converter fails, it can cause significant engine performance issues.

Technical Details

Modern vehicles are equipped with catalytic converter temperature sensors to monitor the operating temperature of the catalytic converter. Typically there are two sensors – one upstream (before the catalytic converter) and one downstream (after the catalytic converter).

The Powertrain Control Module (PCM) uses input from these sensors to infer catalytic converter efficiency. It expects the downstream sensor reading to be cooler than the upstream sensor by a certain amount. If the correlation between the two sensors is out of expected range, code P046B will set.

Catalytic converter temperature is a key parameter for the PCM to regulate fuel trim and other emission control functions. A problem with the temperature sensors or an overheating catalytic converter can cause increased emissions and reduced converter lifespan.

Common Causes

Potential causes for code P046B include:

• Faulty upstream or downstream catalytic converter temperature sensor
• Wiring issue between the sensors and PCM
• Exhaust leak before or near the catalytic converter
• Overheating catalytic converter due to rich fuel mixture or misfires
• Malfunctioning PCM (rare)

Diagnosis Steps

To properly diagnose code P046B, a mechanic should:

1. Scan for all trouble codes and document freeze frame data.
2. Visually inspect the catalytic converter temperature sensor wiring and connectors. Repair any damaged wiring or loose connections.
3. Check live data stream to compare upstream vs downstream temperature sensor readings. Readings should be stable with downstream about 50-100°F (10-38°C) cooler than upstream.
4. If sensor readings are erratic or out of range, test the sensors with an ohmmeter. Replace faulty sensors.
5. Check for exhaust leaks at the exhaust manifold, oxygen sensor bosses, and pipe flanges before the catalytic converter. Repair any leaks found.
6. Inspect the catalytic converter for signs of overheating like discoloration, warping, or rattling. An overheated converter will need to be replaced.
7. If no other issues are found, a faulty PCM may be the cause, although this is rare. Consult a dealer for PCM diagnosis and replacement.

Repair Costs

The cost to diagnose and repair code P046B will depend on the root cause, but common estimates are:

• Catalytic converter temperature sensor: $100-300 each ($85-250 EUR)
• Exhaust leak repair: $100-300 ($85-250 EUR)
• Catalytic converter replacement: $500-2000 ($420-1680 EUR)
• 1-3 hours labor: $75-225 ($63-190 EUR)

Prevention and Other Considerations

Keeping your vehicle well-maintained with regular tune-ups and replacing worn spark plugs, ignition wires, and oxygen sensors can help prevent catalytic converter issues. Avoiding driving with a misfiring engine is also important.

Code P046B may appear along with other codes related to fuel trim (P0171, P0172), misfires (P0300-P0308), or catalytic converter efficiency (P0420, P0430). Addressing all codes together is key to fully resolving the problem.

Frequently Asked Questions About P046B

What does OBD-II code P046B mean?

Code P046B stands for “Catalyst Temperature Sensor 1/2 Correlation (Bank 2).” It indicates that the powertrain control module (PCM) has detected a discrepancy between the temperature signals from the upstream and downstream catalytic converter temperature sensors on bank 2 (the side of the engine that does not contain cylinder #1).

What are the common symptoms of code P046B?

Common symptoms include:

• Check engine light illumination
• Reduced fuel efficiency
• Increased exhaust emissions
• In some cases, there may be no noticeable symptoms

Is it safe to drive with code P046B?

While code P046B itself does not typically cause drivability issues, it indicates a problem with the catalytic converter system that can lead to increased emissions and potential catalytic converter damage if left unaddressed. It’s best to diagnose and repair the issue promptly.

What are the potential causes of code P046B?

Potential causes include:

• Faulty upstream or downstream catalytic converter temperature sensor
• Wiring issues such as open or shorted circuits related to the sensors
• Exhaust leaks before or near the catalytic converter
• Overheating catalytic converter
• Issues with the diesel exhaust fluid (DEF) system on diesel vehicles
• Rarely, a faulty PCM

How do you diagnose code P046B?

Diagnosis steps include:

1. Check for related codes, especially those pertaining to the DEF system on diesel vehicles. Address those first.
2. Visually inspect the wiring and connectors for the catalytic converter temperature sensors. Repair any damage.
3. Using a scan tool, compare the temperature readings from the upstream and downstream sensors. They should show a notable difference.
4. Physically test the exhaust temperatures with an infrared thermometer and compare to scan tool readings. Replace sensors that don’t match.
5. If the sensors test okay, use a DVOM to check the sensor circuits for shorts, opens, or high resistance. Repair wiring as needed.

What tools are needed to diagnose P046B?

To properly diagnose P046B, you will need:

• An OBD-II scanner
• A digital volt-ohmmeter (DVOM)
• An infrared thermometer
• A reliable source of vehicle repair information

How much does it cost to fix code P046B?

The cost to repair P046B depends on the root cause. Common cost estimates include:

• Catalytic converter temperature sensor replacement: $100-300 each
• Wiring repairs: $50-200
• Catalytic converter replacement (if faulty): $500-2000

Labor costs are typically 1-3 hours, or $75-225.

Can code P046B cause damage to the catalytic converter?

Code P046B itself does not damage the catalytic converter. However, the underlying issue that triggered the code, such as an exhaust leak or overheating condition, can lead to premature catalytic converter failure if not addressed.

What is the difference between upstream and downstream catalytic converter temperature sensors?

The upstream sensor, also known as sensor 1, measures the temperature of the exhaust gases entering the catalytic converter. The downstream sensor, or sensor 2, measures the temperature exiting the converter. In a properly functioning system, the downstream temperature should be notably higher than the upstream.

Why does the PCM monitor catalytic converter temperatures?

The PCM uses the temperature data to infer catalytic converter efficiency. By comparing the upstream and downstream temperatures, it can determine if the converter is operating properly to reduce emissions. Temperature monitoring is especially critical on diesel vehicles that use DEF injection.

Can a malfunctioning catalytic converter cause code P046B?

Yes, a faulty catalytic converter that is not efficiently processing exhaust gases can cause temperature readings that are out of expected range, triggering code P046B.

What other codes may appear along with P046B?

Related codes may include:

• P0420 – Catalyst System Efficiency Below Threshold (Bank 1)
• P0430 – Catalyst System Efficiency Below Threshold (Bank 2)
• P2002 – Diesel Particulate Filter Efficiency Below Threshold (Bank 1)
• P2003 – Diesel Particulate Filter Efficiency Below Threshold (Bank 2)
• Codes related to the DEF system on diesel vehicles

Can a blown fuse cause code P046B?

A blown fuse related to the catalytic converter temperature sensor circuits can cause code P046B to set. Check the vehicle’s fuse box diagram and test any suspect fuses with a multimeter.

How do you test a catalytic converter temperature sensor?

To test a catalytic converter temperature sensor:

1. Disconnect the sensor electrical connector.
2. Using a DVOM, measure the resistance between the sensor signal terminal and ground. Compare to manufacturer specifications, which are typically 200-3000 ohms at room temperature.
3. If readings are out of spec, replace the sensor.

What are the common failure points for catalytic converter temperature sensor wiring?

Common failure points include:

• Rubbing or chafing on hot exhaust components
• Corrosion at electrical connectors
• Wiring pinched between components
• Solder joint cracks on PCB-type sensors

Carefully inspect the entire wiring harness for damage.

Can code P046B be caused by an engine misfire?

A severe misfire condition can cause the catalytic converter to overheat, potentially damaging the temperature sensors or triggering code P046B. Misfires should be diagnosed and repaired promptly to prevent catalytic converter damage.

Is the repair procedure for code P046B different on diesel engines?

The basic diagnostic procedure is similar for diesel and gasoline engines. However, diesel engines equipped with DEF injection rely more heavily on the catalytic converter temperature sensors for proper emissions control. Any faults in the DEF system should be addressed before diagnosing P046B.

Can a software update fix code P046B?

In rare cases, a PCM software update may resolve code P046B if the issue is caused by a programming error. However, most instances of P046B are caused by hardware faults that require physical repairs.

How often should catalytic converter temperature sensors be replaced?

Catalytic converter temperature sensors are not maintenance items and do not have a specified service interval. They should be replaced only when testing indicates a failure.

Can code P046B be prevented?

While not all instances of P046B are preventable, following these tips can help minimize risk:

• Address any exhaust leaks promptly
• Repair engine misfires at the first sign of an issue
• On diesel engines, follow the manufacturer’s recommended maintenance for the DEF system
• Avoid using low-quality or contaminated DEF fluid
• Have any catalytic converter issues diagnosed and repaired promptly