SERVICE TIPS: DURAMAX EGR VALVE/DPF
Two critical elements that need to be checked out at 100,000 miles are the EGR valve and the DPF.
Hasten says to run a computerized flow test on the DPF filter tol show if the filter in the exhaust stream needs cleaning or replacing.
A number of companies across the country offer such filter cleaning/refurbishing, which costs a fraction of a replacement.
Contrary to what most performance-minded Duramax owners believe, the EGR doesn’t affect horsepower. I does, however, play an integral role in maximizing both engine life and fuel economy.
(Blocking and/or removing the EGR is a federal violation most companies can’t afford to get caught breaking.)
Halsten says the Duramax EGR only operates at idle and cruise where it allows “inert gases” into the cylinders so the engine can run leaner for optimum mpg while keeping the combustion chamber cooler and reducing NOx.
“The EGR is automatically turned off under heavier throttle load and WOT to maximize power. “It’s during long idle periods the EGR manifold will collect oily soot,” explains Halsten.
“Extreme soot buildup can cause the EGR valve to stick and affect idle quality. But the EGR system doesn’t affect engine power because that’s all bypassed when the ECM senses 8 to 10 pounds boost or WOT.”
Halsten says to replace the EGR valve when it throws a P0401 (EGR Flow Insufficient) code, which usually doesn’t happen until after 100,000 miles.
If the EGR valve needs to replaced, it’s most likely time to clean the EGR cooler.
“A clogged EGR cooler will trip both EGR and MAF sensor codes, affecting performance. So you should remove the EGR cooler when the valve is replaced and give it a thorough cleaning,” advises Halsten.”The cleaning and flushing takes a couple hours to do it right.”
Downstream is the DPF filter, which Halsten advises should be checked for flow restriction when the EGR is replaced and the cooler cleaned. “Most GM service techs can use their diagnostic equipment to check flow in and out of the DPF without touching it.”
If flow is below acceptable levels, cut the DPF out and have it cleaned by a specialty service such as FSX (fsxinc.com) or DPF Regeneration (dpfregeneration.com), which is 3 to 4 times cheaper than having it replaced with a new one.