Peterbilt 389 / Cummins ISX, Paccar MX-13 etc. FAQs

DEF (diesel exhaust fluid) is an important component of the emission control system on modern diesel engines. It helps to reduce harmful emissions, such as nitrogen oxides, by breaking them down into harmless nitrogen and water. If the DEF system becomes contaminated, it can cause problems with the emission control system and may result in failed regenerations, excessive or not enough DEF consumption, 5mph derate, DEF crystallization build up in the SCR system etc. In this article, we will discuss the most common causes of DEF contamination in your Peterbilt Semi Truck with a Cummins ISX engine and how to diagnose and fix the issue. I. Common Causes of DEF Contamination There are several common causes of DEF contamination in your Peterbilt Semi Truck with a Cummins ISX engine. Here are a few: Mixing DEF with other fluids: DEF should never be mixed with other fluids, as it can cause contamination. Using incorrect concentration, low-quality or expired DEF: Using DEF that has an incorrect ratio of water to urea, is past its expiration date or of poor quality can lead to contamination. Dirty DEF pumps at a fill station: If you fill up your DEF from a station, watch out for dirty nozzles that can transfer debris to the inside of your DEF tank. Contaminated DEF storage containers: If the DEF is stored in containers that are not clean or are contaminated with other fluids, it can lead to contamination. DEF pump issues: If the DEF pump is not functioning properly, it can lead to contamination of the DEF. DEF filter issues: If the DEF filter is old, dirty, or plugged up, it can cause contamination of the DEF. II. Diagnosing and Fixing DEF Contamination To diagnose and fix DEF contamination in your Peterbilt Semi Truck with a Cummins ISX engine, you can follow these steps: Check the DEF level using the gauge or dipstick. If it is low, add DEF fluid as needed to bring it to the proper level. Check the DEF fluid for any signs of contamination, such as a change in color or consistency. If the DEF is contaminated, it will need to be replaced with a new, high-quality batch. Inspect the DEF storage containers to ensure that they are clean and free from contamination. Check the DEF pump for any signs of malfunction, debris or damage, such as leaks or faulty seals. If the DEF pump is found to be faulty, it will need to be repaired or replaced. Check the DEF concentration mixture. DEF should be mixed with deionized water to a concentration of 32.5% +/- 1%. If the DEF concentration is incorrect, it can cause contamination. To troubleshoot this issue, you can have the DEF tested with a test strip or use a diagnostic scan tool to check the DEF concentration. TIP: verify the scan tool parameters with a test strip, don’t rely on what the computer tells you.  If the DEF concentration is incorrect, you will need to drain and discard the contaminated DEF properly. Depending on what the contamination is, you may also need to rinse your DEF tank with distilled water. Afterward, replace the DEF filter. Fill the DEF tank with new high-quality DEF (bottled DEF preferably, not from a bulk pump at a fill station) Again depending on the extent of the contamination, you may need to purge the DEF system to clear the lines and injector of the bad DEF.  Check the DEF filter for any signs of contamination. If the DEF filter is old, dirty, or plugged up, it can cause contamination of the DEF. Clean or replace the DEF filter as needed to resolve the issue. Have the DEF system inspected by a professional to determine the cause of the contamination and have any faulty components repaired or replaced as needed.

Step 1: Check for fault codes related to the DPF pressure sensor. Use a diagnostic scan tool to retrieve fault codes related to the DPF pressure sensor. Determine if the sensor is causing the issue by checking for codes related to the DPF pressure sensor. Step 2: Perform a forced regeneration and monitor the parameters throughout the process. It may first be necessary to clear the fault codes first if the scan tool allows. During the regeneration process, be sure to monitor the temperatures, pressures, flow rates, etc. If the regeneration does not complete successfully or the parameters are not correct, it may be an indication of a problem with the DPF pressure sensor or another component of the emission control system. Step 3: Check/test the DPF pressure sensor. Inspect the sensor for any signs of damage or debris. Cracks and leaking components of the sensor are common due to the extreme heat on the plastic sensor. Also check the DPF pressure sensor tubes for soot build up, this is very common and causes the same issues. To clean you can just blow the tubes through with air, scrub them with a cylindrical brush or flush with a degreaser / solvent. Note that just because the sensor looks fine does not mean internally it is fine. Refer to manufacturer specifications to test the DPF pressure sensor to determine if it puts out the correct resistance across the pins etc. Replace the sensor if needed. Step 4: Check the wiring and connectors for the DPF pressure sensor. Inspect the wiring and connectors for any signs of damage, melting or corrosion. Repair or replace the wiring and connectors as needed. Refer to the manufacturer specifications for a pin out diagram to check voltage, resistance etc. Step 5: Check for issues with the exhaust system. Inspect the exhaust system for any issues, such as leaks or blockages. This can change the pressure in the system and blame it on the DPF pressure sensor Repair or replace any faulty components as needed. Step 6: Check for issues with the DPF or DOC. Probably the most expensive solution, but unfortunately if you’re seeing this code, are required to regen very often (like everyday) along with other codes, it may be best to get your DPF or DOC (diesel oxidation catalyst) inspected. If the DPF or DOC pass inspection you may just need to get the filters cleaned to remove the excess “ash” or soot. If you suspect that there may be an issue with the DPF, have the vehicle inspected by a professional. Have any faulty components repaired or replaced as needed.

I. Common Causes of DEF Contamination There are several common causes of DEF contamination in your Peterbilt 386, 389, 567, 579 etc. with a Paccar MX-13 engine. Here are a few: Mixing DEF with other fluids: DEF should never be mixed with other fluids, as it can cause contamination. Using incorrect concentration, low-quality or expired DEF: Using DEF that has an incorrect ratio of water to urea, is past its expiration date or of poor quality can lead to contamination. Dirty DEF pumps at a fill station: If you fill up your DEF from a station, watch out for dirty nozzles that can transfer debris to the inside of your DEF tank. Contaminated DEF storage containers: If the DEF is stored in containers that are not clean or are contaminated with other fluids, it can lead to contamination. DEF pump issues: If the DEF pump is not functioning properly, it can lead to contamination of the DEF. DEF filter issues: If the DEF filter is old, dirty, or plugged up, it can cause contamination of the DEF. II. Diagnosing and Fixing DEF Contamination To diagnose and fix DEF contamination in your Peterbilt 386, 389, 567, 579 etc. with a Paccar MX-13 engine, you can follow these steps: Check the DEF level using the gauge or dipstick. If it is low, add DEF fluid as needed to bring it to the proper level. Check the DEF fluid for any signs of contamination, such as a change in color or consistency. If the DEF is contaminated, it will need to be replaced with a new, high-quality batch. Inspect the DEF storage containers to ensure that they are clean and free from contamination. Check the DEF pump for any signs of malfunction, debris or damage, such as leaks or faulty seals. If the DEF pump is found to be faulty, it will need to be repaired or replaced. Check the DEF concentration mixture. DEF should be mixed with deionized water to a concentration of 32.5% +/- 1%. If the DEF concentration is incorrect, it can cause contamination. To troubleshoot this issue, you can have the DEF tested with a test strip or use a diagnostic scan tool to check the DEF concentration. TIP: verify the scan tool parameters with a test strip, don’t rely on what the computer tells you.  If the DEF concentration is incorrect, you will need to drain and discard the contaminated DEF properly. Depending on what the contamination is, you may also need to rinse your DEF tank with distilled water. Afterward, replace the DEF filter. Fill the DEF tank with new high-quality DEF (bottled DEF preferably, not from a bulk pump at a fill station) Again depending on the extent of the contamination, you may need to purge the DEF system to clear the lines and injector of the bad DEF.  Check the DEF filter for any signs of contamination. If the DEF filter is old, dirty, or plugged up, it can cause contamination of the DEF. Clean or replace the DEF filter as needed to resolve the issue. Have the DEF system inspected by a professional to determine the cause of the contamination and have any faulty components repaired or replaced as needed.