P0474 – Exhaust Pressure Sensor Intermittent

Urgency and Driving Considerations

When the P0474 code is triggered, it indicates an issue with the exhaust pressure sensor circuit. While not extremely urgent, it's best to address it soon to prevent potential damage to the catalytic converter and maintain optimal engine performance and fuel efficiency. You can typically continue driving in the short term, but prolonged driving without fixing the underlying issue can lead to more serious problems. It's advisable to have the code diagnosed and repaired within a few days to a week if possible.

Code Details

The P0474 is a generic powertrain code that applies to vehicles equipped with variable nozzle turbochargers, including many Ford, Cummins, Mercedes, and Nissan diesel engines from the mid-2000s onward. It may also appear on some gasoline turbo engines. The code indicates the exhaust pressure sensor signal is not matching the expected intake manifold or ambient air pressure at various points during engine operation.

While the general definition is consistent, the specific troubleshooting steps, parts, and repair procedures can vary somewhat by vehicle make and model. Related codes that may appear alongside P0474 include:

• P0470 – Exhaust Pressure Sensor Circuit
• P0471 – Exhaust Pressure Sensor Circuit Range/Performance
• P0472 – Exhaust Pressure Sensor Circuit Low
• P0473 – Exhaust Pressure Sensor Circuit High

Parts Involved

The main components related to the P0474 code are:

• Exhaust Pressure Sensor – Measures the pressure in the exhaust system. Typically mounted on or near the turbocharger or exhaust manifold.
• Exhaust Back Pressure Valve/Regulator – Controls exhaust flow to the turbocharger based on signals from the exhaust pressure sensor and PCM.
• Wiring and Connectors – Carries signals between the sensor, valve, and PCM.
• PCM (Powertrain Control Module) – The vehicle's main computer that monitors sensors and controls engine functions.

Common Causes

Potential causes of a P0474 code include:

• Clogged exhaust back pressure sensor tube
• Faulty exhaust pressure sensor
• Damaged wiring or connectors in the exhaust pressure sensor circuit
• Shorted or open exhaust pressure sensor harness
• Leaking intake manifold or turbocharger connection hoses
• Rarely, a faulty PCM

Symptoms

Symptoms you may notice with a P0474 include:

• Check engine light illuminated
• Reduced engine performance
• Insufficient turbocharger boost pressure
• Inability to perform a manual DPF regeneration
• Possibly a no-start condition if unable to regen the DPF

Diagnosis

To properly diagnose a P0474 code:

1. Scan for all codes and note any others that may be related.

2. Visually inspect the exhaust pressure sensor, wiring, and connectors. Look for any obvious damage, corrosion, or loose connections.

3. Clear the code and see if it returns. If not, an intermittent connection was likely the cause.

4. Check for any technical service bulletins (TSBs) related to the code for your vehicle. Some may require a PCM update.

5. Locate the exhaust pressure sensor and disconnect the tube connecting it to the exhaust. Try to blow through it. If clogged, carefully clean it out or replace it.

6. Test the sensor's power, ground, and signal circuits with a DVOM. The signal should be around 5V. Repair any circuits that are out of spec.

7. If the circuits test okay, use a scan tool to monitor the sensor signal while wiggling the harness. If the code returns, there is likely an intermittent short in the harness that needs to be repaired.

8. If the code persists after harness repair, suspect a faulty sensor or possibly the PCM.

Repair Options

Fixes for a P0474 code may involve:

• Cleaning or replacing a clogged exhaust pressure sensor tube
• Replacing a faulty exhaust pressure sensor ($38-$243)
• Repairing damaged wiring or connectors in the sensor circuit
• Replacing a shorted or open sensor harness
• Repairing intake or turbo boost leaks
• Rarely, replacing a faulty PCM

Many of these repairs can be done DIY with some mechanical skill to save on labor costs. Expect to pay between $95-$605 for a professional repair, depending on the specific issue and labor rates.

Prevention

To help prevent P0474 and related codes from occurring:

• Maintain the exhaust and emissions systems per the manufacturer's service schedule
• Address any boost or exhaust leaks promptly
• Keep the engine tuned up to prevent excessive soot buildup in the exhaust
• Avoid aftermarket tunes that may alter expected sensor values

By understanding the P0474 code's causes, symptoms, diagnosis, and repair, you can more quickly resolve the issue and keep your vehicle running at its best. As always, when in doubt, consult a professional technician for further assistance.

Frequently Asked Questions about P0474

What does the P0474 code mean?

The P0474 code indicates that the exhaust pressure sensor circuit is experiencing intermittent or erratic behavior. This sensor measures pressure in the exhaust system and sends a signal to the powertrain control module (PCM). When the signal does not match expected values based on other sensor inputs, the P0474 code is triggered.

What vehicles are most likely to experience a P0474 code?

P0474 is most common on vehicles equipped with variable nozzle turbochargers, including many Ford, Cummins, Mercedes, and Nissan diesel engines from the mid-2000s onward. It may also appear on some gasoline turbo engines. While more prevalent on certain makes, it can potentially occur on any vehicle with an exhaust pressure sensor.

Is it safe to drive with a P0474 code?

In most cases, you can continue driving in the short term with a P0474 code. However, it's best to diagnose and fix the issue within a few days to a week if possible. Driving for prolonged periods without addressing the underlying problem can lead to reduced performance, decreased fuel efficiency, and potential catalytic converter damage.

What are the common symptoms of a P0474 code?

Common symptoms include:

• Illuminated check engine light
• Reduced engine performance and lack of power
• Insufficient turbocharger boost pressure
• Inability to perform a manual DPF regeneration
• Rough idling or stalling in some cases

What causes a P0474 code to be triggered?

Potential causes of a P0474 code include:

• Clogged exhaust back pressure sensor tube
• Faulty exhaust pressure sensor
• Damaged wiring or loose connectors in the sensor circuit
• Shorted or open exhaust pressure sensor harness
• Leaking intake manifold or turbocharger hoses
• Rarely, a faulty PCM

How do you diagnose a P0474 code?

To diagnose a P0474 code:

1. Scan for all codes and note any others present.
2. Visually inspect the exhaust pressure sensor, wiring, and connectors for damage, corrosion, or loose connections.
3. Clear the code and see if it returns. If not, it was likely an intermittent issue.
4. Check for related technical service bulletins that may require a PCM update.
5. Test the sensor tube for clogs. Clean or replace if needed.
6. Test the sensor's power, ground, and signal circuits with a DVOM. Repair wiring as needed.
7. Use a scan tool to monitor the sensor signal while wiggling the harness to check for shorts.
8. If the code persists, suspect a faulty sensor or PCM.

Can a P0474 code cause a vehicle to fail an emissions test?

Yes, a stored P0474 code will likely cause your vehicle to fail an emissions test. The issue must be repaired and the code cleared before retesting.

What are some other codes that may appear along with P0474?

Related codes that may be stored alongside P0474 include:

• P0470 – Exhaust Pressure Sensor Circuit
• P0471 – Exhaust Pressure Sensor Range/Performance
• P0472 – Exhaust Pressure Sensor Circuit Low
• P0473 – Exhaust Pressure Sensor Circuit High

Can a P0474 code be caused by an aftermarket tune?

Yes, aftermarket tunes that alter expected sensor values can potentially trigger a P0474 code. If you suspect a tune is the culprit, reflashing the PCM back to stock may resolve the issue. Always use caution with aftermarket tuning.

How much does it typically cost to diagnose and repair a P0474 code?

Diagnosis of a P0474 code can cost around $150 at a shop or dealership. If you need to replace the exhaust pressure sensor, expect to pay between $95-$605 for parts and labor, depending on the specific vehicle and repair needed. Many of the diagnostic steps and some repairs can be done DIY to save on labor costs.

Can a blown turbo cause a P0474 code?

While a catastrophic turbo failure is unlikely to directly set a P0474 code, issues like worn bearings, cracked housings, or leaking seals that affect exhaust backpressure and flow could potentially trigger the code in some cases. A thorough diagnosis is needed to pinpoint the exact cause.

Is the exhaust back pressure sensor the same as an EGR pressure sensor?

No, while both sensors deal with exhaust gases, they serve different purposes and are located in separate areas. The exhaust back pressure sensor measures pressure in the exhaust system, typically near the turbocharger or manifold. An EGR pressure sensor measures pressure specifically in the exhaust gas recirculation system.

Can a clogged catalytic converter cause a P0474 code?

Yes, a severely clogged catalytic converter that restricts exhaust flow could potentially trigger a P0474 code by altering the expected pressure readings. However, other codes related to catalyst efficiency would likely be stored as well. A backpressure test can help diagnose a blocked converter.

Is a P0474 code serious?

While a P0474 code does not typically represent an urgent issue, it should still be addressed in a timely manner. Driving with an unresolved P0474 can lead to drivability issues, increased emissions, and potential damage to components like the turbocharger or catalytic converter over time.

What does an exhaust pressure sensor do?

The exhaust pressure sensor measures the pressure of gases in the exhaust system. It sends this information to the PCM, which uses it along with other sensor data to regulate fuel trim, turbo boost, EGR flow, and other functions for optimal performance and emissions. A faulty or intermittent signal can disrupt these processes.

Can a P0474 code affect fuel economy?

Yes, an issue that triggers a P0474 code can potentially impact fuel economy by affecting the engine's ability to efficiently regulate factors like turbo boost and fuel trim. Resolving the underlying problem should restore normal fuel efficiency.

How often should the exhaust pressure sensor be replaced?

There is no specific maintenance schedule for replacing an exhaust pressure sensor. They are typically replaced on an as-needed basis when diagnosed as faulty. However, keeping up with regular service like air filter changes can help prevent premature sensor failures by minimizing soot buildup in the exhaust stream.

What tools are needed to diagnose a P0474 code?

To properly diagnose a P0474 code, you will need:

• An OBD-II scanner to check for codes
• A digital volt-ohm meter (DVOM) to test wiring and circuits
• A smoke machine or leak detector to check for boost/exhaust leaks
• Basic hand tools to access and remove the sensor if needed

Having a factory service manual or wiring diagram for your specific vehicle can also be very helpful.

Can a P0474 code clear itself?

In some cases, a P0474 code may clear itself if the condition that triggered it was intermittent and does not recur. However, it's still important to diagnose the issue, as intermittent faults can become more frequent and severe over time if the underlying cause is not addressed.

What should I do if a P0474 code keeps coming back after clearing?

If a P0474 code persists after initial diagnosis and repair, there are a few steps to take:

1. Double check your work and ensure all wiring/connections are secure.
2. Perform a more thorough inspection of the exhaust pressure sensor, wiring harness, and other components for intermittent faults.
3. Check for any related pending codes that may point to the root cause.
4. Consider less common causes like a faulty PCM.
5. Consult a professional technician for further diagnosis if needed.

By understanding the P0474 code's causes, symptoms, and diagnostic steps, you can more effectively troubleshoot and resolve the issue when it arises. As always, proper diagnosis is key to avoiding unnecessary repairs and ensuring reliable vehicle performance.