I read your “limping home” reply on the Mercedes E 320 in the July magazine and wonder if you could pass comment on my own experiences – perhaps it is the same things that need exploring? I have a 2004 VW Transporter Kombi 2.5 TDI 130bhp. Every now and again it goes into limp home mode. Standard answer is to switch the engine off, then restart and it is fine again – until the next time. This might happen twice in one day, and then not for another three months or so. Perhaps it is starting to get slightly more frequent in the last year or so, and I am therefore becoming more nervous of the idea of it happening whilst overtaking. The garage says it is the turbocharger, or that’s what their diagnostics apparently said. However, it first started happening about five or six years ago, and the vehicle now has 125,000 miles on the clock. I would have thought that a seriously faulty turbo would have bitten the dust well before now, so I have been reluctant to spend money replacing it. The trigger seems to be either heavy acceleration, or lifting off after a heavy acceleration, preferably coupled with a corner. But of course I can’t do this to order when I want to demonstrate it to a garage! About six months ago, we removed and drained the fuel tank, in case there was a diesel bug causing problems, and replaced the fuel filter. The tank was fine though, according to the garage, except for being really dirty black inside. Since I am writing to you, you can tell this possible solution didn’t work. I will plead guilty to usually using low engine revs – after all, 2000rpm is 70mph in sixth gear – as low engine revs in a high gear was the way I was taught to drive diesels. Your comments will be greatly appreciated.
Thanks,
Wiclif

Amazing that you have put up with this for so long! I’m not sure what sort of garage you are speaking of, and whose diagnostics pointed to the turbocharger, but the suggestion is/was not very specific, so maybe it was an all-makes diagnostic set-up that was incapable of digging any deeper? Not everyone is aware that the simpler diagnostic systems used by many independent garages are incapable of the full in-depth communication that systems like VAG-COM for Volkswagen Group cars offer, and the diagnosis may therefore often only be pretty general. I would think that a diagnostic check with VAG-COM would be more specific and possibly identify what I suspect is the problem, an intermittently faulty turbocharger pressure sensor, that is falsely detecting an over boost situation, and dropping the engine into limp-home mode – probably code 16618 Boost Pressure Regulation or EC OBD2 code P0234. The action of dropping into limp-home should be recorded in the OBD system and then reported on interrogation. If it’s not the actual sensor, it could be a bad connection in the circuit, or even something dodgy in the main ECU – which I hope not! Fitting a new boost pressure sensor should cost you around £100, I would imagine. Hope this points you in the right direction! Do please let me know, if you can!
Doc Diesel