If your Volvo VNL semi truck is experiencing issues with derate mode, it can be frustrating and disrupt your ability to operate the vehicle. Derate mode is a safety feature that limits the engine's power output to protect it from damage. In this article, we will go over some steps you can take to troubleshoot and repair the possible causes of 5mph derate on a Cummins ISX engine.
Steps to Troubleshoot and Repair Derate Mode Issues:
- Check for fault codes: Using a diagnostic scan tool, check for any fault codes that may be causing the derate mode. These codes can help to identify the specific issue with the engine.
- Perform a visual inspection: Look for any visible problems that may be causing the derate mode, such as damaged wiring or components.
- Check the intake air system: Make sure that the intake air system does not have any leaks and is not blocked or restricted. A leak or restriction in the intake air system can cause the engine to go into derate mode.
- Check the exhaust system: Make sure that the exhaust system is not blocked, restricted or having any leaks on gaskets or clamps etc.. A restriction or leak in the exhaust system can cause the engine to go into derate mode.
- Check the fuel system: Make sure that the fuel system is functioning properly and that there are no issues with the fuel filters or fuel lines.
- Check the EGR system: Make sure that the EGR (exhaust gas recirculation) system is functioning properly. Issues with the EGR system can cause the engine to go into derate mode.
- Check the turbocharger: Make sure that the turbocharger is functioning properly and that there are no issues with the VGT (variable geometry turbo) or actuator.
- Check the NOx sensors: Make sure that the NOx (nitrogen oxide) sensors are functioning properly and that there are no issues with the wiring or connections.
- Perform a parked regen: If all other checks have been completed and the issue with the derate mode persists, perform a parked regeneration (regen) and monitor the parameters to see if any of them do not meet the standards. This should help bring the root cause of the derate to the surface (the fault code should appear). Or the ECM / ACM may recognize that there are no current issues and it may remove the derate.
- Perform an SCR efficiency test: If the regen passes and no fault codes are present, perform an SCR (selective catalytic reduction) efficiency test and again monitor the parameters.This should help bring the root cause of the derate to the surface (the fault code should appear). Or the ECM / ACM may recognize that there are no current issues and it may remove the derate.
It is important to note that both the forced regen and SCR efficiency test may need to be performed multiple times in order to either force the fault code that caused the derate to appear or, if no faults are found, to remove the derate. If the derate mode persists after multiple attempts to perform these tests, it may be necessary to seek the assistance of a professional diesel technician to further diagnose the issue.
Caution:
Performing multiple forced regens and SCR efficiency tests can put a major strain on the DPF and DOC filters and the truck as a whole. These tests can be hard on the engine and exhaust system and should be done with caution. It is recommended to only perform these tests as a last resort and under the guidance of a professional diesel technician. Performing these tests can potentially cause further damage to the truck and may not necessarily solve the issue with the derate mode.
