Later tractors, engines, loaders, excavators and telehandlers may use DPF, EGR, SCR and DEF/AdBlue systems to control emissions. When one of these systems develops a fault, the machine may display warning lamps, fault codes, reduced power or a request for regeneration.
Emissions systems are model-specific and may contain very hot exhaust components, pressurised dosing systems and sensitive sensors. Use the correct workshop or diagnostic manual. Do not disable, remove or bypass emissions equipment.
1. Main Emissions Systems
Depending on machine and year, the engine may use:
- EGR – Exhaust Gas Recirculation
- DOC – Diesel Oxidation Catalyst
- DPF – Diesel Particulate Filter
- SCR – Selective Catalytic Reduction
- DEF / AdBlue dosing
- NOx sensors
- Exhaust temperature sensors
2. DPF Fault Codes
DPF-related codes may involve:
- High soot load
- Excess ash loading
- Differential pressure sensor
- Exhaust temperature sensors
- Regeneration incomplete
- Regeneration inhibited
3. Soot vs Ash
These are different.
Soot
Carbon produced during combustion. It can normally be reduced by regeneration.
Ash
Non-combustible residue that accumulates over time and eventually requires approved cleaning or filter replacement.
4. Regeneration
A regeneration raises exhaust temperature to burn soot from the DPF.
Types may include:
- Passive regeneration
- Automatic active regeneration
- Parked regeneration
- Service regeneration
5. Regeneration Inhibited
A machine may refuse regeneration because of:
- Active engine fault
- Low fuel level
- Incorrect coolant temperature
- Exhaust temperature sensor fault
- DPF pressure sensor fault
- Unsafe operating condition
A forced regeneration should only be carried out when the diagnostic procedure confirms that it is appropriate and the machine is in a safe location away from combustible material.
6. DPF Differential Pressure Sensor
The controller uses pressure difference across the filter to estimate restriction.
Faults Can Be Caused By
- Failed sensor
- Blocked pressure pipes
- Split hose
- Condensation
- Electrical wiring fault
- Actually blocked DPF
Do not replace the DPF before checking the pressure-sensing circuit.
7. Exhaust Temperature Sensors
These sensors help control and protect regeneration.
Faults may involve:
- Open circuit
- Short circuit
- Implausible reading
- Slow response
- Actual excessive temperature
8. EGR Fault Codes
EGR systems may generate codes for:
- Valve position
- Flow too high
- Flow too low
- Valve stuck
- Position sensor fault
- EGR cooler performance
9. EGR Valve Sticking
Possible causes include:
- Carbon deposits
- Actuator failure
- Position sensor fault
- Wiring problem
- Mechanical sticking
10. EGR Cooler Problems
Symptoms can include:
- Coolant loss
- Steam or white exhaust smoke
- Temperature-related codes
- Reduced EGR performance
Follow the manufacturer test procedure before condemning the cooler.
11. SCR and DEF / AdBlue Systems
SCR reduces NOx emissions using DEF/AdBlue injected into the exhaust.
System Components May Include
- DEF tank
- Level/temperature sensor
- DEF pump
- Dosing injector
- Heated lines
- NOx sensors
- SCR catalyst
12. DEF Quality Faults
Possible causes include:
- Contaminated fluid
- Wrong fluid
- Water dilution
- Old or improperly stored DEF
- Sensor fault
Use only DEF/AdBlue meeting the specification required by the manufacturer.
13. DEF Crystallisation
White crystalline deposits can form around leaks or dried dosing fluid.
Check:
- Dosing injector
- Line connections
- Pump module
- Tank fittings
14. DEF Heater Faults
Machines operating in cold conditions may use heated:
- Tank
- Lines
- Pump
Heater faults can cause dosing problems in freezing conditions.
15. NOx Sensor Faults
NOx sensors may fail because of:
- Sensor failure
- Wiring damage
- Connector corrosion
- Exhaust leaks
- System performance fault
Do not assume every NOx-related code means the sensor itself is defective.
16. Exhaust Leaks
Leaks before or around emissions sensors can affect readings.
Inspect
- Manifold joints
- Turbo connections
- DPF clamps
- Sensor bosses
- SCR joints
17. Boost and Air-System Faults Can Trigger Emissions Codes
Problems such as:
- Split boost hose
- Blocked air filter
- Turbo fault
- MAP sensor fault
- MAF sensor fault
can alter combustion enough to create secondary emissions faults.
18. Fuel-System Faults Can Also Be the Root Cause
Check for:
- Low rail pressure
- Injector faults
- Water in fuel
- Restricted fuel filter
Poor combustion creates more soot and can overload the aftertreatment system.
19. Repeated Regeneration Requests
If regeneration is needed too often, possible causes include:
- Engine not reaching operating temperature
- Excessive idling
- Very light-load work
- Injector or air-system fault
- DPF pressure sensor problem
- DPF ash accumulation
20. Machines That Spend Long Periods Idling
Extended low-load operation can reduce exhaust temperature and increase soot accumulation.
Follow the machine’s recommended operating and regeneration practices.
21. Engine Derate
Some emissions faults cause reduced engine power.
Derate may be triggered by:
- High soot load
- DEF system fault
- NOx fault
- Missed regeneration
- Severe sensor or dosing fault
22. Warning Lamps and Countdown Messages
Some machines display escalating warnings before severe derate.
Record:
- Exact lamp
- Fault code
- Hours/minutes remaining if shown
- Active/stored status
23. Do Not Clear Codes Before Recording Them
Before clearing anything, record:
- All emissions codes
- Related engine codes
- Soot load if available
- DEF level
- Exhaust temperatures
- Differential pressure
24. Use Live Data
Useful live data may include:
- DPF differential pressure
- Soot load
- Exhaust temperature
- EGR commanded vs actual position
- DEF pressure
- NOx readings
Compare readings with the diagnostic manual.
25. Sensor Plausibility
A sensor can be electrically connected yet still give an implausible reading.
Examples
- Exhaust sensor reading ambient when engine is hot
- DPF pressure showing high with engine stopped
- DEF level changing unrealistically
- EGR actual position not following command
26. Service Regeneration
A workshop service regeneration may require:
- Diagnostic tool
- Correct coolant temperature
- No active blocking faults
- Safe open area
- Machine stationary
Follow the exact procedure.
27. DPF Cleaning
If ash loading is excessive, the DPF may require:
- Approved off-machine cleaning
- Inspection for damage
- Replacement if beyond service limits
Regeneration cannot remove ash.
28. After Repair
Depending on the machine, repair may need:
- Code clearing
- Sensor reset
- DPF replacement reset
- DEF system prime
- Calibration
- Regeneration
Only carry out the procedures specified for that system.
29. Best Diagnostic Order
- Record all active and stored codes.
- Check battery and charging voltage.
- Check engine faults that could create excess soot.
- Inspect connectors and harness.
- Check relevant sensors and live data.
- Confirm actual pressure/temperature where possible.
- Repair the root fault.
- Carry out required reset or regeneration.
- Verify codes do not return.
30. Emissions Fault Checklist
| Area | Check |
|---|---|
| Fault codes | Recorded exactly before clearing. |
| DPF | Soot/ash status and pressure data checked. |
| EGR | Command, position and mechanical operation checked. |
| DEF/AdBlue | Correct fluid, level and dosing system checked. |
| NOx sensors | Wiring, exhaust leaks and live data checked. |
| Engine condition | Fuel, air and boost faults ruled out. |
| Regeneration | Performed only when permitted and safe. |
| Final verification | No active codes after repair and test. |
Related Agrimanual Manuals
DPF, EGR, SCR and DEF diagnostic procedures vary greatly between engines and machines.
- Search Agrimanual DPF diagnostic manuals
- Search Agrimanual emissions workshop manuals
- Search Agrimanual manuals containing fault codes
- Request a manual if your machine is not listed
Frequently Asked Questions
Does a DPF code mean the DPF needs replacing?
No. Check differential pressure sensing, temperature sensors, engine condition and soot/ash status before condemning the filter.
Can regeneration remove ash?
No. Regeneration burns soot. Ash remains and eventually requires approved cleaning or filter replacement.
Why does my machine keep asking for regeneration?
Possible causes include prolonged idling, low-load work, engine faults creating excess soot, sensor faults or a DPF approaching its ash limit.
Does an EGR fault always mean the valve is bad?
No. Wiring, position sensing, carbon deposits and flow problems can all create EGR codes.
Should emissions equipment be removed if it keeps causing faults?
No. Diagnose and repair the system using the correct workshop information. Removal or bypass can be unlawful and can create further engine-control problems.
Treat the code as evidence, not the answer. Check the engine, sensors and aftertreatment system together before replacing expensive emissions components.