Cheap DIY Fix for P208E

我的VW Sharan 是 2015 年的2.0 TDI 柴油引擎，跟很多車主一樣， 尿素系統隨著時間過去， 在保固期之後就跳出了故障燈。

用檢測電腦可以查到有兩個故障碼， 一個是 P203B AdBlue的液位偵測信號不可信， 另一個是 P205C  AdBlue 溫度感測器對地短路。

P203B 的問題很多人知道可以用加熱水的方式處理， 因為他的原因就是尿素溶液結晶在感測器上面，導致信號的不穩定。

但是 P205C 這個溫度感測器的問題就比較討厭， 這個感測器位置在尿素桶裡面， 他和液位偵測以及加熱線都在同一個模組上面。

車廠的解決方式都是拆下尿素桶， 把這個模組換掉， 所以不管是材料錢還是工錢都讓人吃不消，而且根據大家的經驗， 換過之後這個問題仍是有機會復發的。

所以很多人的選擇是寫程式把尿素系統關掉，就不再使用， 把這個問題一勞永逸的解決。

我自己的經驗是， 這個問題如果你不處理， 除了儀表板上面的引擎燈會一直亮著之外，其實日常使用沒有影響。

尿素也不再消耗， 也不會因為尿素耗盡而導致引擎無法啟動， 因次我就這樣開了兩年多， 一直到...

下班時發動引擎， 儀表板跳出了新的燈號， 顯示出Adblue 不足， 將在1000 公里後無法發動引擎。

好吧， 這個問題非修理不可了，總不能冒險發不動引擎。

掛上檢測電腦發現了一個新的故障碼，P208E 尿素噴射閥卡在關閉位置。

其實尿素系統已經很長時間沒有動作了，也沒有鎖引擎， 但是因為一個沒有用的系統裡面有個元件也故障了， 反而要鎖引擎?

這個邏輯其實也很奇怪， 如果這個環保系統真的那麼嚴格， 那應該任何一個部分只要導致系統無法運作都應該要強制車主去修復， 但也沒有。反而是一個停止作動的系統中多一個壞掉的元件才開始有強制的力道去要求修復。

總之， 這個問題是非修理不可了。

身為一個機械工程師， 也跟光機電整合搞了二十多年的我來說，這個問題如果就只是拿錢出來解決就太可惜了。

先來解決P208E 噴射閥卡住的問題， 預期能解決掉這個問題的話， 至少應該能回復到過去兩年的狀態， 可以繼續撐著。

尿素噴射閥就在中央扶手的正下方， 當然從車內是摸不到的， 因為他是將尿素噴入 觸媒轉換器的裝置， 是裝在排氣管路上的元件。

所以把車子撐起來，固定架將車子固定之後， 用風扇把排氣管溫度降低之後，才有辦法拆下噴射閥檢修。

噴射閥只有一個 2 Pin 的connector作為 開關控制，還有尿素管路的接頭， 跟排氣管相接的部分有個扣環固定住兩個法蘭面。

解下電氣接頭之後， 雙指壓住尿素管路的塑膠扣環就可以把尿素管和噴射閥分離， 接下來就是用4mm的內六角扳手把扣環鬆開， 這樣就可以拆下噴射閥。

拆下之後其實噴射閥看起來狀況並不差， 沒有什麼尿素結晶， 也沒有什麼炭灰並不髒

， 看來 DPF 還是有用。

但是他卡住了，可能是兩年多都沒有動作， 所以卡住了。

初步用清潔劑加上毛刷把看得見的髒汙清掉，然後用電源供應器從2Pin 接頭送電看看是不是有動作，結果安安靜靜沒有動作， 看來是卡住了。

接著試著分解看看， 如果能拆開就更容易把卡住的部分鬆開。

但是這個是暴露在車底的元件，他的防水性應該是做得很好， 即使鬆開了扣片也只是將接頭鬆開， 對於內部卡住的電磁閥沒有幫助，所以裝回去，用超音波清洗機試試看。

將噴射閥的電氣接頭朝上， 放進超音波清洗機， 加上一點清潔劑就震個幾分鐘，看起來似乎有些毛刷處理不了的汙垢被震出來。

接上電源供應器再上電試試看， 還是不行，沒有動作的聲音。

思考著還有甚麼方法可以讓卡住的東西鬆開， 除了清潔之外還可以潤滑， 但是這個噴射閥是要噴尿素溶液的， 如果加了WD-40去潤滑， 之後會不會因為排氣管高溫造成潤滑油固化反雸卡住更嚴重? 決定還是不要這樣做

回到卡住這個問題，卡住就是要移動的東西沒有足夠的力量去克服外力，這個外力可能就是因為長時間沒有動作導致有異物沾黏使得需要克服的力量增加， 而原本可以正常動作的電磁閥力量就不足以推開。

所以要解決卡住的問題， 除了讓卡住的外力藉由清潔的動作去恢復之外， 再來就是增加冬作的力量。以電磁閥來說就是增加電壓， 讓線圈的力量更大一點， 只要不燒壞線圈， 這個動作沒有後遺症。

電磁閥的操作電壓從 12V 開始往上調升， 一邊用反覆開關的方式去聽看看是否有動作。Sharan 的電系正常情況下， 我觀察到最高會到 14.9V， 鬆油門滑行的時候是回充電壓最高的時候， 所以我估計在16V 以內應該都不至於燒線圈， 更何況這只是常溫下的暫態操作， 相較於排氣管上的工作條件來說， 不應該是問題。

果然隨著電壓的上升， 在15.x V 的時候， 聽到了電磁閥動作的聲音。再把電壓降回到 12V 測試， 也是可以正常的操作了。

到此， 依照順序反向裝回車上，發動引擎之後， 再用檢設電腦將故障碼消除之後， P208E 這個故障碼就消失了，暫時沒有引擎發動不了的問題。

My VW Sharan is a 2015 2.0 TDI diesel engine. Like many Sharan owners, the SCR system developed a fault after the warranty period, resulting in the engine malfunction light appearing. The diagnostic computer showed two error codes: P203B, indicating an unreliable signal for the  AdBlue level detection, and P205C, indicating a ground short circuit in the AdBlue temperature sensor.

Many people know that the issue with P203B can be resolved by using heated water added into the  AdBlue tank. This problem occurs when  AdBlue crystallizes on the sensor, causing signal instability. However, the problem with P205C, the temperature sensor, is more troublesome. This sensor is located inside the  AdBlue tank and is part of the same module as the level detection and heating element. The solution provided by car dealers is to remove the AdBlue tank and replace the entire module, which is costly in terms of materials and labor. Moreover, based on people's experiences, even after replacing the module, the problem can still recur.

Therefore, many people choose to disable the SCR system by programming it to permanently shut down. This provides a permanent solution to the problem.

In my own experience, if you don't address this issue, besides the engine light staying on in the dashboard, it doesn't affect daily use. The AdBlue is no longer consumed, and the engine won't fail to start due to AdBlue depletion. So I continued driving like this for over two years, until...

Last Thursday, when I started the engine after work, a new warning light appeared on the dashboard, indicating low Adblue and that the engine wouldn't start after 1000 kilometers. Well, this problem needs to be repaired. I can't take the risk of not being able to start the engine.

I connected the diagnostic computer and found a new error code, P208E, indicating that the AdBlue injection valve was stuck in the closed position. In fact, the SCR system had been inactive for a long time, and it didn't lock the engine. But now, because one component in an unused system had a malfunction, it was causing the engine to lock?

The logic behind this is strange. If this environmental system is so strict, then any part that causes the system to fail should force the car owner to repair it, but it doesn't. Instead, when there's a malfunctioning component in a system that has stopped functioning, there is a sudden insistence on repairing it.

In any case, this problem needs to be repaired. As a mechanical engineer with over twenty years of experience in opto-mechatronics integration, it would be a pity to solve this problem just by throwing money at it.

First, I need to solve the issue with the stuck injection valve, with the expectation that if I can resolve this problem, I should be able to return to the state I had for the past two years and continue driving.

The AdBlue injection valve is located directly below the center armrest. Of course, it cannot be accessed from inside the car because it injects AdBlue into the catalytic converter and is a component installed on the exhaust pipe. So, I need to lift the car, secure it on jack stands, and use a fan to cool down the exhaust pipe before I can remove the injection valve for inspection.

The injection valve has only one 2-pin connector for control and a AdBlue pipe connection. The part that connects to the exhaust pipe is secured by a clamp. After disconnecting the electrical connector, I can separate the AdBlue pipe from the injection valve by pressing the plastic clamp with my fingers. Next, I use a 4mm hex wrench to loosen the clamp ring, allowing me to remove the injection valve.

Upon inspection, the injection valve didn't seem to be in bad condition. There were no AdBlue crystals or significant soot deposits. It appeared that the Diesel Particulate Filter (DPF) was still functioning properly. However, it was stuck, possibly due to not being in operation for over two years. I initially cleaned visible dirt using a cleaning agent and a brush. Then, I applied power to the valve through the 2-pin connector to see if it would respond. Unfortunately, there was no movement or sound, indicating that it was still stuck.

Next, I tried to disassemble it  and see if I could easily loosen the stuck parts by disassembling them. However, this component is exposed underneath the car, and its waterproofing should be well done. Even if I loosen the clips, it will only disconnect the connectors and won't help with the stuck electromagnetic valve inside. So, I put it back and tried using an ultrasonic cleaning machine.

Place the electrical connector of the injector valve facing upwards and place it in the ultrasonic cleaning machine. Add some cleaning agent and let it vibrate for a few minutes. It seems that some dirt that couldn't be removed with a brush has been shaken loose.

Connect it back to the power supply and test it again, but there is still no response or sound of movement.

I considered other methods to free the stuck component. Besides cleaning, lubrication was another option. However, since the injection valve is designed to spray AdBlue, using WD-40 or any lubricant could potentially cause it to solidify and worsen the problem due to the high temperatures in the exhaust pipe. Therefore, I decided against using lubrication.

Returning to the issue of the valve being stuck, it meant that the moving part lacked sufficient force to overcome external resistance. This resistance could have increased due to foreign matter accumulation during the prolonged inactivity. The electromagnetic valve's original force might not be enough to push it open.

To solve the sticking problem, I needed to not only restore the external forces through cleaning but also increase the electromagnetic force. For the electromagnetic valve, this meant increasing the voltage to provide a stronger current to the coil. As long as I didn't burn out the coil, there would be no side effects to this temporary operation at room temperature.

I started increasing the operating voltage of the electromagnetic valve from 12V while repeatedly toggling the switch to listen for any movement. Under normal electrical conditions in the Sharan, I observed that the voltage would reach a maximum of 14.9V. The highest voltage occurred during regenerative braking when coasting, so I estimated that anything below 16V should be safe for the coil. Moreover, this was only a transient operation at room temperature, which shouldn't be a problem compared to the working conditions in the exhaust pipe.

As expected, as the voltage increased, I heard the sound of the electromagnetic valve operating at around 15.x V. I then lowered the voltage back to 12V for testing, and the valve operated normally.

After completing the above steps, I proceeded to reassemble everything back onto the vehicle in the correct order. Once the reassembly was done, I started the engine. Afterward, I used a diagnostic computer to clear the fault codes. As a result, the P208E fault code disappeared, and there was no longer an issue with the engine failing to start, at least for the time being.