Duramax Diesel Exhaust System Fluid Injectors

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The new 6.6L Duramax diesel engine that debuted in the 2010 Chevrolet Express and GMC Savana and 2011 Chevrolet Silverado and GMC Sierra is equipped with an advanced exhaust aftertreatment system to reduce emissions. The aftertreatment system features two diesel exhaust system injectors. 

The Diesel Exhaust Aftertreatment Fuel Injector, also called the Q57 Indirect Fuel Injector or the Hydrocarbon Injector, supports Diesel Particulate Filter (DPF) regeneration -- reducing particulate matter, or soot, in the exhaust -- by adding fuel to the engine exhaust system. On the previous Duramax diesel engine, this was accomplished using the cylinder injectors via post injection. Now, the Exhaust Aftertreatment Fuel Injector sprays fuel into the turbo downpipe.

The other new injector is the Diesel Emission Reduction Fluid Injector, also called the Diesel Exhaust Fluid (DEF) injector. It injects DEF into the exhaust gases to suppress oxides of nitrogen (NOx) emissions. The DEF injector is located downstream of the Diesel Oxidation Catalyst (DOC) and upstream of the Selective Catalyst Reduction (SCR) system/DPF. 

Diesel Exhaust Aftertreatment Fuel Injector

The Diesel Exhaust Aftertreatment Fuel Injector, or Hydrocarbon Injector (HCI), is a new type of dedicated diesel fuel injector used during DPF regenerations only. The fuel injector threads into the turbo downpipe tube.

The HCI is commanded on by the Engine Control Module (ECM) and injects fuel directly into the engine's exhaust gases downstream of the engine's turbo. Fuel to the injector is supplied from the low-pressure side of the high-pressure fuel pump. The injector's control valve is located over the right rear cylinder head.

The HCI supplies a measured quantity of fuel into the exhaust gas only during enabled regeneration events. The DOC converts this added fuel into the heat that's needed to regenerate the DPF by incinerating accumulated soot. DOC temperatures are monitored during regeneration by two Exhaust Gas Temperature sensors (EGT 1 and EGT 2). If temperatures are too low, DTC P0420 (Catalyst System Low Efficiency) will set.

The HCI system operates only when enabled (regen enable). On 2010-2011 model year vehicles, the system isn't used during service regenerations. The service regeneration cycle is driven by post-injection from the engine's eight diesel fuel injectors (just as on the 2007-2010 Duramax engine). For 2012, the HCI system is used for both enabled and service regenerations.


Successful on-road DPF regeneration relies on proper HCI function. For Duramax diesel DTCs such as P0420, P24A0 (Closed Loop DPF Regeneration Control at Limit - Temperature Too Low), or P2463 (Diesel Particulate Filter Soot Level Accumulation), the indirect fuel injector should be diagnosed for proper function as described in the appropriate Service Information. Test the HCI for proper flow quantity prior to replacing the DOC to avoid misdiagnosis.

If the HCI isn't injecting enough fuel, the regeneration-measured exhaust temperatures (as determined by EGT 1 and 2) may be too low and set DTC P0420. Prolonged HCI difficulty may also set DTC P2463 or P2459 (Diesel Particulate Filter Regeneration Too Often).

Diesel Emission Reduction Fluid Injector

The Diesel Emission Reduction Fluid Injector, or Diesel Exhaust Fluid (DEF) injector, sprays DEF into the exhaust for distribution into the SCR catalyst. The DEF injector is mounted just downstream of the DOC canister on the DOC exhaust pipe. (Fig. 4) To help maintain DEF injector integrity, let the vehicle idle for 10 minutes immediately after a service regeneration before turning off the engine. This allows time for the DEF injector to cool.

Fig. 4

When servicing the DEF tank and DEF injector, do not overstress the DEF injector's plastic inlet nipple. Make sure the emission reduction fluid exhaust supply pipe retains slack. The nipple can fracture if overstressed.

When removing the DEF supply pipe from the DEF injector, it may be necessary to flush the connector with water to ease release of the supply pipe from the injector nipple. 

Diesel Exhaust Fluid

DEF (urea) is a clear solution of approximately 32% ammonia and 68% water. When the water evaporates from the fluid, white crystalline deposits (some deposits may appear darker depending on soot incorporation) of urea remain. (Fig. 5) Since this fluid travels through the DEF injector, it is common for these deposits to form at the exit nozzle of the injector and, in some cases, inside the injector. 

Fig. 5

The presence of deposits over the DEF injector's exit nozzle alone shouldn't prompt an injector replacement. Rather, perform the DEF Quantity Test -- refer to the Emission Reduction Fluid Injector Quantity Test in the Service Information -- to diagnose the DEF injector for performance issues. 

The urea deposits are usually soluble in water. Once the DEF system begins spraying fluid again, these deposits dissolve and clear from the nozzle exit. This includes the crystals that may form on the inside of the DEF injector as well as at the exit nozzle.

If these deposits interfere with DEF injection, perform the quantity test a few times to allow for the DEF crystals to dissolve. 

Temperature also helps dissolve the crystals deposits. Urea melts at about 275° F (135° C). Since the quantity test is performed when the vehicle is off, it may take longer for the crystals to dissolve than it would on a running vehicle.

Cold Temperatures

When the 6.6L Duramax diesel engine is operated in extremely cold ambient temperatures, a Service Exhaust Fluid System message may be displayed on the Driver Information Center. DTC P204F (Reductant System Performance) may set with possible vehicle speed limiting. Temperatures would have to be under -4° F (-20° C) for long periods of time.

If this message is displayed, complete the current Service Information diagnosis for any DTCs or symptoms found. The vehicle may actually have a low reductant fluid pressure, which would also set DTC P204F. 

For 2010-2011 models only, a new calibration was released to improve extreme cold temperature conditions related to DTC P204F. 2012 models have updated calibrations. 

Other factors that could contribute to the setting of DTC P204F include the use of an aftermarket winter cover or a combination of a winter cover and a snow plow (if the vehicle is equipped with a snow plow, a winter cover must not be used). This may allow the system to sense artificially high underhood temperatures, which could potentially prevent the DEF heaters from turning on and thawing the reductant fluid as required. 

- Thanks to Brian Fuller and B.J. Lackey

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This page contains a single entry by Blog Post published on January 31, 2012 9:33 PM.

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