FREQUENTLY ASKED QUESTIONS ABOUT p0402 DURAMAXThe p0402 Duramax, diagnostic trouble code usually indicates that an “excessive exhaust gas recirculation flow has been detected”. This code can pretty much be triggered under any condition and is usually detected by a mechanic by evaluating the various causes behind this condition. Now, for our reader’s reference, we have answered some of the most frequently asked questions about p0402 Duramax.
What Does The P0402 Code Usually Mean For Engine Condition?
The p0402 generic code generally indicates that the engine exhaust gas recirculation valve is flowing too much recirculated exhaust gases when it is commanded to open the flow of gases in the engine.
What Are Some Common Causes Of Excessive Exhaust Gas Circulation Flow?
1) The EGR valve can sometimes open much more than needed due to a blocked vacuum diaphragm in the EGR vacuum which backs the pressure valve.
2) The EGR temperature in rare situations starts registering too much temperature change especially when the EGR valve is open, this leads to excessive back pressure on the EGR system.
What Are The Symptoms Of A P0402 Code?
1) The check engine light often illuminates which sets the code in ECM memory.
2) The engine exhaust pipe sometimes ends up having exhaust leaks at the backpressure transducer.
How Can A Mechanic Diagnose This Condition?
1) Mechanics usually disconnect and check to see if the EGR valve vacuum is getting controlled when the control solenoids are open on a light-to-medium acceleration or not.
2) They sometimes also check the exhaust catalyst for damage or excessive back pressure on the EGR system.
3) Mechanics make it a point to check the vacuum hose, wiring, control solenoids and EGR temperature sensors when checking for the p0402 condition.
In a nutshell, this code is triggered when the EGR temperature sensors see much more temperature change that the EGR commands. In fact, this condition is quite common in situations when the EGR backpressure control valve has to deal with a burnt diaphragm due to partly blocked catalyst.
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