SPN 4335 – DEF Air Pressure

Understanding Fault Code SPN 4335

Fault code SPN 4335 indicates an issue with the Exhaust Gas Recirculation (EGR) position sensor circuit. When this code is triggered, it's important to diagnose and address the problem promptly to prevent potential engine damage. However, in most cases, you can safely drive the vehicle to a repair shop unless other severe symptoms are present.

Urgency and Severity

In general, you can continue driving a vehicle with an active SPN 4335 code if it is running normally otherwise. However, it's best to diagnose and repair the issue as soon as possible, especially if you notice symptoms like:

• Rough idle
• Reduced fuel economy
• Increased emissions
• Illuminated check engine light

If the vehicle goes into "limp mode" or has significantly reduced power, it's best to stop driving and have it towed to a mechanic for diagnosis and repair.

Code Specifics

SPN 4335 is a generic powertrain code that applies to most vehicles equipped with an EGR system, including cars and trucks from major makes like Ford, GM, Chrysler, Toyota, Honda, etc. The code indicates that the powertrain control module (PCM) has detected an issue with the EGR position sensor signal being out of the expected range.

Parts Involved

The main components related to code SPN 4335 are:

• EGR Valve: Allows exhaust gases to recirculate back into the engine intake to lower combustion temperatures and reduce NOx emissions.
• EGR Position Sensor: Measures the actual position of the EGR valve pintle and sends a signal to the PCM. Usually a variable resistor or Hall effect sensor.
• PCM: Controls the EGR system and monitors the EGR position sensor signal.

Common Causes

Some typical causes for code SPN 4335 include:

1. Faulty EGR position sensor
2. Wiring issues in the EGR position sensor circuit (shorts, opens, high resistance)
3. Stuck or binding EGR valve
4. Carbon buildup in the EGR system
5. Malfunctioning PCM (rare)

Diagnosis Steps

To properly diagnose fault code SPN 4335, follow these steps:

1. Scan for codes and document freeze frame data.
2. Visually inspect the EGR valve and position sensor for damage or heavy carbon deposits.
3. Test the EGR valve movement and note any sticking or binding.
4. Check the resistance of the EGR position sensor and compare to specifications (typically 0-10 kΩ).
5. Verify reference voltage and ground signals at the sensor connector.
6. Check for continuity and measure resistance on the EGR position sensor wiring harness.

Repair Solutions

Depending on the diagnosed cause, repairs for SPN 4335 may involve:

• Replacing the EGR position sensor
• Cleaning or replacing the EGR valve
• Repairing wiring or connectors in the EGR position sensor circuit
• Cleaning carbon deposits from the EGR system and intake
• Reflashing or replacing the PCM (rare)

Prevention and Cost

To prevent EGR-related issues, regularly service the vehicle and use high-quality fuel. Cleaning the EGR system every 50,000-80,000 km (30,000-50,000 miles) can help avoid carbon buildup.

Repair costs for SPN 4335 can vary depending on the root cause:

• EGR position sensor: $80-$150 / €75-€140
• EGR valve: $250-$500 / €235-€470
• Wiring repairs: $50-$200 / €45-€190
• EGR system cleaning: $100-$250 / €95-€235

Related Issues

Other fault codes and symptoms that may appear along with SPN 4335 include:

• P0400 – Exhaust Gas Recirculation Flow Malfunction
• P0401 – Exhaust Gas Recirculation Flow Insufficient Detected
• P0402 – Exhaust Gas Recirculation Flow Excessive Detected
• Misfires
• Hesitation under acceleration

By understanding fault code SPN 4335 and following proper diagnostic and repair procedures, technicians can effectively resolve EGR position sensor issues and keep vehicles running efficiently while minimizing emissions.

Frequently Asked Questions about SPN 4335

What does fault code SPN 4335 indicate?

SPN 4335 indicates an issue with the diesel exhaust fluid (DEF) system air pressure. Specifically, it means the DEF system air pressure is below the normal operating range.

What are the common symptoms of SPN 4335?

Common symptoms of SPN 4335 include:

• Illuminated check engine light
• Reduced engine power (derate)
• Poor DEF quality message
• Increased DEF consumption

What systems are affected by SPN 4335?

SPN 4335 affects the selective catalytic reduction (SCR) system, which uses DEF fluid to reduce NOx emissions. The main components involved are the DEF tank, pump, pressure sensor, dosing valve, and associated lines and wiring.

Is it safe to drive with an active SPN 4335 code?

It depends on the severity. In some cases, you may be able to drive the vehicle to a repair shop if no other symptoms are present. However, if the engine is derated or other codes are active, it's best to stop driving and have the vehicle diagnosed as soon as possible to prevent further damage.

What are the common causes of low DEF system air pressure?

Common causes of low DEF system air pressure include:

1. Faulty air pressure control valve
2. Leaks in the air supply lines or fittings
3. Malfunctioning air compressor
4. Clogged air filter or dryer
5. Faulty DEF pump

How do you diagnose the root cause of SPN 4335?

To diagnose SPN 4335, follow these steps:

1. Check for air leaks in lines and fittings
2. Verify air compressor output pressure
3. Test operation of the air pressure control valve
4. Check for restrictions in the air filter and dryer
5. Measure DEF pressure and compare to specs

What repairs are needed to fix low DEF air pressure?

Repairs for SPN 4335 may include:

• Replacing the air pressure control valve
• Repairing air leaks in lines or fittings
• Servicing the air compressor
• Replacing plugged air filters or dryers
• Replacing a faulty DEF pump

How much does it typically cost to fix SPN 4335?

The cost to repair SPN 4335 varies depending on the root cause. An air pressure control valve may cost $200-$400, while a DEF pump could be $800-$1500 including labor. Air leak repairs are usually inexpensive ($50-$200) unless lines need to be replaced.

Can low DEF air pressure cause other fault codes?

Yes, low DEF air pressure can trigger other fault codes related to the SCR system, such as SPN 4334 (DEF pressure below range), SPN 4094 (NOx efficiency below threshold), and SPN 4364 (SCR efficiency below threshold).

What is the normal operating pressure for the DEF system air supply?

The normal operating pressure for the DEF system air supply is typically 80-120 psi (550-825 kPa). The exact specification varies by engine make and model.

How can I prevent issues with the DEF system air pressure?

To prevent issues with DEF system air pressure:

• Perform regular maintenance on the air compressor and filters
• Fix any air leaks promptly
• Use high-quality DEF fluid from reputable suppliers
• Avoid running the DEF tank empty
• Keep electrical connectors clean and secure

What component is most likely to cause SPN 4335?

The air pressure control valve is the most common cause of SPN 4335. This valve regulates the pressure supplied to the DEF system. If it fails or becomes stuck, it can allow air pressure to drop below specs.

Can low air pressure affect DEF injection and dosing?

Yes, proper air pressure is needed for the DEF pump to build pressure and the dosing valve to atomize the fluid. If air pressure is too low, the DEF may not be injected at the proper rate, leading to incomplete NOx reduction and other SCR system issues.

What is the difference between SPN 4334 and SPN 4335?

SPN 4334 indicates low DEF fluid pressure, while SPN 4335 points to low DEF air pressure. They are related but distinct issues. Air pressure is supplied to the DEF system to help pump and inject the fluid, so low air pressure can lead to low DEF pressure.

Can a bad DEF pump cause low air pressure?

Not directly, as the pump does not generate the air pressure. However, a failing DEF pump may not be able to maintain adequate fluid pressure even with normal air pressure supplied. Always diagnose the air and fluid sides of the system separately.

How do you check for air leaks in the DEF system?

To check for air leaks, perform a visual inspection of all lines and fittings, looking for cracks, kinks, or loose connections. Use soapy water to pinpoint leaks while the system is pressurized. You can also measure pressure drop after shutting off the compressor.

What are the most common places for DEF system air leaks?

Air leaks are most likely to occur at:

• Fittings and connections
• Rubber hoses and lines
• Air compressor gaskets and seals
• Air dryer or filter housing

Is it necessary to use OEM parts when replacing DEF system components?

While aftermarket parts may be less expensive, it is generally recommended to use OEM components for critical emissions systems like SCR. This ensures proper fit, function, and compliance with regulations. Consult your owner's manual or dealer for specific recommendations.

How often should the DEF system air filter and dryer be replaced?

The service interval for the DEF system air filter and dryer varies by application and environment. Typical recommendations range from 1-2 years or 100,000-200,000 miles. Check your maintenance schedule and monitor performance to optimize change intervals.

What should I do if the SPN 4335 code keeps coming back after repairs?

If SPN 4335 reappears after repairs, it indicates the root cause was not properly addressed. Double check your diagnosis and ensure all parts were replaced with the correct specifications. Look for additional air leaks or restrictions. In rare cases, a faulty control module could be setting the code erroneously.