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P0402 Code – What Does It Mean & How To Fix It

This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.

Definition

If your car has thrown the P0402 error code, you might be wondering what it means. This code means “Exhaust Gas Recirculation Flow Excessive Detected” and usually refers to a faulty EGR valve.

Meaning

P0402 is an OBD-II code that lights up when the ECM, or Engine Control Module, senses that there is a problem with the EGR (Exhaust Gas Recirculation) valve. Usually, it means that the valve could be malfunctioning and allowing too much exhaust gas to recirculate through the engine and intake manifold.  

Causes

This error code is usually caused by one of the three main problems: 

First, the DPFE (differential pressure) sensor might be faulty and need to be replaced. In this instance, there is actually no performance issue – just a bad sensor. This is the easiest, best-case scenario.

Second, there might be some form of blockage in the EGR. This blockage is most likely some form of carbon build-up that can occur through the accumulation of particles over time, but it could also be due to something else getting lodged in that part of the engine.

Finally, the EGR valve itself might be broken, and not opening due to a lack of vacuum.

Symptoms

Depending on the actual problem, you might have one or two symptome.

If it it just a faulty sensor, the only detectable symptom is the indicator light that there is a problem in the engine (usually a “Check Engine” light or “Service Soon” indicator).

If there is an actual performance issue – such as a faulty valve or a blockage – then you might notice an engine hesitation, especially when accelerating or operating at high speeds.

Diagnosis

In order to accurately diagnose the problem with this code, there are a handful of steps to follow:

First, check the freeze-frame data. This data can give you valuable real-time information about engine performance and irregularities.

Second, clear the codes and run the car again. This road test can help verify whether it’s a real problem or just a glitch. If the error code is thrown again, then this indicates a real problem. If not, it was probably just a glitch (which happens more often than you would think).

Third, perform a visual inspection of all affected parts. These parts include the vacuum hoses, wiring, control solenoid, the EGR valve and its connections along with the back pressure transducer and EGR temperature sensor.

Next, disconnect the EGR valve vacuum to evaluate its performance. Can it be controlled to the valve only when it is open fully, or even when the control solenoid is open on light-to-medium acceleration?

Then, check the exhaust catalyst. Look for damage that might be causing a malfunction. Also, check for excessive back pressure on the entire EGR system.

Finally, remove the EGR valve and temperature sensor. Look inside for a carbon buildup that could be forcing the EGR valve to open or remain open. Inspect the EGR bleed port as well t e ee if it might be blocked, which would interfere with its ability to get rid of any vacuum.

Common mistakes

As with any repair, there are a few mistakes that are common to make, which can make matters worse. 

The first common mistake is replacing the EGR valve without checking the EGR pressure transducer. Without checking the pressure first, you can’t really be certain that the valve is faulty to begin with, leading to a repair that might not need to be made. 

The other common mistake is not checking for carbon buildup before replacing the valve. In this case, not only do you waste time and money by replacing something that doesn’t need it – the problem will still be there when you are finished!

How serious is this?

The severity of this code depends a lot in what’s actually wrong with the vehicle. If it ist just a faulty sensor, you probably will have nothing to worry about other than an emissions test. Other than that, yo should have no other concern.

If there is a problem with the valve or the opening around the valve, you might notice performance problems. These can be anywhere from rough idling, poor performance when accelerating, or even the car losing power and not starting. 

What repairs can fix the code?

Depending on the actual problem, there are several ways this code can be fixed.

It can be fixed by replacing the EGR valve, replacing the broken catalyst, replacing the EGR backpressuvre control valve, cleaning out the carbon buld-up or replacing the EGR temperature sensor.re control valve

Related codes

None listed.