Diesel Emissions Repair That Finds the Cause
Diesel emissions repair on a Powerstroke, Duramax or Cummins is some of the most complex work to diagnose and repair. Sometimes it is a failed DPF or catalytic converter, and sometimes it is something upstream of the aftertreatment system. Either way, it takes a methodical diagnostic approach to repair the system accurately.
Five parts, one system, and each one leans on the others
The engine computer runs it all as one system, so when one part fails, parts downstream can be damaged as well. Pick a part.
EGR valve and EGR cooler
The EGR system sends a measured amount of exhaust back into the intake to cut NOx, The EGR cooler uses engine coolant to lower the exhaust gas temperature before sending it back into the intake system.
Cooler failures: EGR cooler replacement.
EGR valves can clog with carbon or have an electrical failure. When the EGR cooler fails it can pressurize the cooling system and send coolant into the intake, which gives off a sweet smell.
DOC: the oxidation converter
The DOC sits ahead of the filter and burns off unburned fuel and carbon monoxide. During an active regen the engine adds fuel late in the cycle, and the DOC burns it to heat the filter clean.
A DOC coated in oil or raw fuel cannot get hot enough to do its job, so regens fail even when the filter is fine.
Diesel particulate filter (DPF)
The DPF traps soot and burns it off during a regen. Ash from engine oil does not burn, so over enough miles every filter needs cleaning or replacement.
Plugged filters and regen trouble: DPF repair.
A filter that plugs early is being fed too much soot from upstream, usually by injectors, the turbo or the EGR system.
SCR converter and DEF
Selective catalytic reduction handles the NOx that EGR leaves behind. DEF sprayed ahead of the SCR converter turns NOx into nitrogen and water.
Heaters, pumps and SCR faults: DEF and SCR system repair.
Heaters fail, dosers crust over and poor fluid sets quality codes. When dosing stops working, the truck warns you, then limits speed or power.
Sensors and wiring
A pressure sensor reads how loaded the DPF is, temperature sensors watch the converters, and NOx sensors check the SCR.
A sensor reading wrong makes the computer regen when it does not need to, skip one it does need, or blame a converter that is fine. A cheap sensor can make an expensive part look dead, so we test before we order.
A plugged filter is often the messenger
Before we begin an emissions repair, we run through the entire system, front to back. We repair the parts that can be proven bad, then run through the system again, front to back, and repeat until it is working properly.
- Dripping or overfueling injectors load the filter faster than a regen can burn it. See diesel injector repair.
- Boost pressure below where it should be, which can cause excess soot. See diesel turbo repair.
- An EGR cooler leaking coolant into the exhaust.
What the dash shows, and what is usually behind it
Most emissions faults show up as a light, a message or more frequent regens.
| What you see | What it often means | Where we look first |
|---|---|---|
| Regens more often than normal, or regens that never finish | The filter loads fast, the exhaust never gets hot enough to clean it, a sensor reads wrong or the air filter is dirty. | All sensor readings, confirming it actually goes into regen, soot load, injector balance, boost and DOC temperatures. |
| Reduced power or limp mode with emissions codes | The truck is seeing a severe emissions system failure, and it can be any of a number of things. | All sensors, plus everything we check for frequent regens. |
| DEF warning with a countdown | The truck thinks dosing or fluid quality has failed. Once reduced power is triggered, it usually limits speed in steps. | Fluid quality, heaters, pump pressure, the doser, the NOx sensors and the EGR system. |
| Cooling system pressure, loss of coolant and carbon in the coolant | Often an EGR cooler leaking into the exhaust. | Pulling the cooler or coolers for a bench pressure test, since confirming a failure takes more pressure than the cooling system runs at. |
| Soot at the tailpipe of a DPF truck | The DPF is bad. Soot getting past the filter can mean a crack. | The filter, which can fail from age, and any upstream fault that overheated it. |
Thin air at foothill and mountain elevations leaves less margin, so a tired turbo or leaking injector can make soot faster. Cold starts and short runs keep exhaust too cool to regen, DEF freezes in a hard winter, and climbing I-70 can create extreme heat that damages or wears components. Unsure where it starts? Begin with diesel diagnostics.
How we work an emissions fault, start to finish
No step starts with buying a part.
Read the truck
Your description, codes, freeze frame and live emissions sensor data on OEM factory scan tools.
Check what feeds it
Injector balance, boost, the EGR valve and cooler, and exhaust leaks. Upstream causes show up here.
Test the hardware
DPF back pressure, converter temperatures, DEF pump pressure, heaters and doser spray.
Repair, then prove it
Repair the failures we can prove, then run through the entire system again, and repeat until it is working properly.
Why two emissions repairs can land far apart
There is no flat price for diesel emissions repair. The bill follows what testing finds.
- Whether multiple parts failed, like coolant that also damaged the DPF
- Which parts failed: sensor, valve, heater, cooler, converter and so on
- Whether the DPF can be cleaned or must be replaced
- How much comes apart to reach it on your platform
- Confirmation of the failure, checking the system over until we are sure
Most emissions work is drop-off. Diagnosis typically takes 24 to 72 hours depending on workload.
Then we call. You hear what needs fixing now, what can wait and where combining repairs saves labor. No work is done without your approval.
We answer the phone Monday to Friday, 8:00 AM to 6:00 PM. If a reduced power countdown starts mid-trip, call us.
What your truck carries depends on its generation
Emissions hardware arrived in stages, so we confirm what is on your truck before we talk parts.
Powerstroke
The 7.3 runs no EGR. The 6.0 and 6.4 are known for EGR cooler failures, and the 6.4 brought Ford's first DPF. The 6.7 carries the full set: EGR, DOC, DPF, SCR and DEF.
Ford Powerstroke repairDuramax
The LB7 runs no EGR, and the LLY added it. The LMM brought the DPF, the LML added SCR and DEF, and the L5P carries the whole system.
Chevy and GMC Duramax repairCummins
The 5.9 runs no EGR or DPF, and only the last years carry a simple converter. The 6.7 arrived in 2007.5 with EGR, a DPF and a NOx adsorber, and 2013 and newer pickups switched to SCR and DEF.
Ram Cummins repairTwo options on the table, and the call was his
From Google, word for word.
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MEL is a Great communicator. They squeezed me in line as we were traveling through to Utah. They analyzed the situation & gave me two choices ! Wow! They gave ME the choice ! They acted on the quickest answer from me & they had me rolling before closing ! FYI: Nothing is cheap in diesel repairs ! Very happy to get rolling & still be rolling ! TY TY THANK YOU !5 STARS
Tell us what your truck is doing
Send the year, the engine and what you are seeing, and we'll get back to you as quickly as we can.
- Year, make and engine
- What it is doing, and when it started
- Any codes or recent repairs
Rather talk it through? Call (303) 808-1563
Emissions questions we hear
Usually because an accurate diagnosis was never done. Whatever filled it is still there: failing injectors, a coolant leak, a bad sensor or short trips will load a clean filter again. A repair that lasts finds that cause first.
No. For safety's sake it is best not to drive the truck, because nobody knows yet what is wrong. The truck may cut power or limit speed to protect itself, and a plugged filter gets worse every mile.
It depends on which part failed and why. A bad sensor and a DPF damaged by coolant are very different bills. After diagnosis you get the cost before any work starts.
DEF freezes in hard cold, so the tank, lines and doser have heaters. A failed heater circuit often only shows on cold foothill mornings, so we test the heaters, fluid quality and pump. Cold also makes it harder for the DPF to get hot enough to run a regen.
Emissions light on or regens that never end? Call before it derates
Call with the codes, how often it regens and how you drive it, or use Request Service to send the details. Or drop us a line right here from the website and we'll get back to you as quickly as we can.