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Greetings everyone,

I own a 2014 W176 2.1 CDI.


I had many troubles since purchasing it, but I am gradually resolving them, having rectified a DPF defect and an exhaust pressure sensor failure.

Currently, when I accelerate the vehicle and enhance the boost, it enters limp mode, sometimes even when idling, though this is less often. However, there are no fault codes to identify the issue. I formerly worked as an HGV technician but departed years ago, and I have been concentrating on a potential boost malfunction. I have inspected the vacuum lines and air intake line for wear, and they seem to be in satisfactory condition.

I conducted a smoke test last night, first on the vacuum line leading to the brake cylinder on the bulkhead, which yielded no issues. Subsequently, I removed the air intake post-air filter for inspection and discovered smoke emanating from the rocker cover gasket, revealing an oil leak previously unknown to me. The leakage was caused by loose screws on the rocker cover. I secured all of them, conducted another smoke test, and there was no longer any leakage. I am contemplating if there should have been any smoke present initially. I have been away from the field for so long that I cannot recall if there is a rationale for smoke entering the air intake pipe and subsequently reaching the rocker cover. I conducted a road test after the repair of the loose screws; nonetheless, the vehicle continues to enter limp mode at elevated RPMs and boost pressure.

Does anybody know whether certain pipes should be used to test various sites? I have never conducted smoke testing previously, thus I am uncertain if I should focus on a particular testing point or many ones. Any assistance would be very appreciated.

This evening, I conducted smoke and vacuum tests at various parts of the vacuum system and am pleased to report that everything is functioning well. Additionally, the air intake system is intact, with no leaks found. I will attempt to replace the boost pressure sensor next.

Does anybody know whether attempting to smoke the exhaust system was worthwhile? It is quite perplexing when there is an absence of problem codes or engine indicators to guide me appropriately.

Which scanner are you utilising?

A comprehensive scan may reveal a code in an other system that is responsible for the problem.


For instance, I have seen the vehicle become unresponsive, with the engine light on, although no engine failure detected.
It has been determined that there exists a subsystem (not the engine), where I identified a failure code related to the exhaust flap.
The code was deleted, resulting in engine failure.

Consequently, it was necessary to repair the exhaust flap to rectify the problem, indicating that the engine management system was influenced by a code recorded in another location.

I have been use an iPhone application in conjunction with a Bluetooth OBD2 scanner. I was reluctant to pay more, since the pricier options seem to include additional control modules.

The performance has improved; it operates more efficiently today, and the engine temperature gauge exhibits less volatility. Throughout this ordeal, the water temperature has been markedly inconsistent, and I am uncertain of the cause. Any insights on this matter would be appreciated. It is now in limp mode whilst addressing the problem. Rectify this, and I may even begin to like her after 18 months!

Recently attached a plug-in scanner (Autolink Autel AL519) used by my workplace for the vehicles; no saved codes detected.

I observed, however, that the MAP sensor reading consistently registered at an ideal 100.0 kPa. It remained stable unlike the other sensors.

The MAF sensor registered 7.87 g/s, which is quite elevated according to a Google search.

Could somebody confirm if it is, please? I may alter both regardless. Eliminate them.