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P0101 implausible signal
Posted to Technical Tips Forum on 10/19/2016 12 Replies

2004 Volkswagen Jetta 1.9 lt turbo diesel came in with a P0101 mass air flow sensor code (implausible signal). The vehicle ran but not well. There was black smoke on acceleration and a noticeable missing condition at cruising speeds. After visually inspecting and following all of the testing procedures with no direct conclusion the final road test and data capture measuring value block 93, channel 2 in deceleration mode from approximately 2300 rpm to 1800 rpm in 5th gear. The desired value is supposed to be 0.95-1.05. The charts for above and below have testing criteria which are different if the values fall above or below the spec. Ours was above, and as we already tested all of the listed components we went looking for a mechanical issue and found what you see in the pictures. Confirming repair directions with the machine shop we sourced a rebuild kit for the head and re-assembled it with new parts as needed. After priming the engine and a oil change, the road test showed the issues were solved. This just goes to show you that the codes you see on the scanner (or the "dreaded" code readers) aren't always the cause of the problem...sometimes it takes a wee bit more work and a little more help than "Google" or "you-tube" lol. By the way this was a BEW engine code.

There is a TSB directly related to the fault code that will give you the testing criteria.

The repair findings were assisted by Dominic and the great team at CAR'S Diagnostic Services.

[2004 Volkswagen Jetta TDI, Engine/Propulsion Photo] [2004 Volkswagen Jetta TDI, Engine/Propulsion Photo] [2004 Volkswagen Jetta TDI, Engine/Propulsion Photo]

Mark Witlox
Witlox Automotive
London, Ontario, Canada

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car Vehicle Data

2004 Volkswagen Jetta TDI 1.9L

Engine1.9 L
Trans5-speed Standard