156 GTA diagnostic codes

[mickl]

Hi, I am having trouble clearing the diagnostic code p 1688 referring to the electrically controlled throttle. It has been to a couple of repairers and no one can clear it from the dash. Any ideas anyone? I am near Newcastle in NSW.
Thanks Mick

[Cool Jesus]

Can you confirm the DTC as P1688 is 'Metering Oil Pump Stepping Motor Circuit Malfunction'
?

[mickl]

Thanks for the very quick response Cool Jesus, I will make a few more enquiries with the mechanic about the code number and it`s description and get back to you 9maybe next week?)
Regards
Mick

[Cool Jesus]

No probs mick. Mind you I have been scratching my head about what on earth the oil pump stepping motor could be. So had another search and came up with the throttle code as you first mentioned.
Anyhow, your not alone with this error. Found this which although doesn't give a definate fix, it may give some insight.

http://www.alfaowner.com/Forum/alfa-gta/233735-fault-code-p1688.html

http://forum.alfa156.net/forum/forum_posts.asp?TID=63715&KW=1688

What I'm reading in those threads is to ensure all connectors are clean and making proper connection. Seems to be a recurring theme with Alfa electronics?

[Cool Jesus]

OK, found another thread which has FIAT ODB codes, so your mech was ruight with the code. The P1688 DTC is the 'motorized throttle (2nd idle learn)' error.

http://www.alfaowner.com/Forum/alfa-gta/174544-p1688-fault-code.html

Now in this latest thread an owner seems to have resolved the issue with a new battery. I had a moment of diagnostic inspiration at this point... over the years I'm reading a lot about requiring good voltage with late and current model Alfas due to the amount of electrics they possess. Now a low battery could equate to an old/bad battery which does require replacement or a faulty alternator. My 147 has an old battery, probably looking at 4-5 yrs old. It recently had a stuffed alternator with a faulty voltage regulator and you could see the electrics surge when it was idling. Evenso, it wasn't throwing up any error codes.

Then I got to think that any poor electrical connection wont allow the flow of current easily and the physics of electricity will use more current to make the flow happen, as far as the battery current will allow. This being the case, we then start getting burnt connectors and wires, as I had with the radiator low speed fan resistor on my spider which melted the plastic connectors and the spade connectors were loose to the point of not holding at all. With a poor connection, if we install a fresh new battery, in effect we are giving it an extra/longer boost of current to complete the poor connection. So what leads to these poor connections. Well, most of the time its within the engine bay that owners are finding problems. A confined area of variable temperature changes and chemicals that can/will effect plastic connectors and the heat/cold that will expand and contract the metal connector pins. So I'm starting to lean towards, and I've read through-out the various forums, that the first diagnostic to perform is to check all the relevant connections.

So the point about my 147 was that my connections must have been OK, as the varying voltage being supplied to the Alfa via the old battery/faulty alternator didn't affect its operation. It probably also helped that I had recently gone through all the connectioons and earths in the engine bay as a preventative maintenance measure. Alternatively, if the battery is low and not holding current then this should effectively shut down the Alfa and not let it run at all, as my 159 did to me with a one year old battery. I've still got the old battery but replaced the 147 alternator all the same and its loving me for it too 

[Cool Jesus]

PS... heres the FIAT DTC codes for those that need it... 

Still searching to figure out what this '2nd idle learn' business is with the throttle

[mickl]

thanks again Cool Jesus, the car has been to another  mechanic who has the right diagnostic equipment and after a new battery and some other adjustments, the problem appeared fixed and the fault was cleared. However, it is back again today and I will be taking it back to the latest mechanic with a full copy of all the suggestions and comments which you have proffered in the various links. I will report back next week. Despite the above issue, the car is a delight to drive, albeit the need to be very careful over speed bumps.
thanks once again, Mick

[Cool Jesus]

We haven't mentioned it, but are you suffering any issues with the alfa? Any symptoms? Could it be something related to either the throttle position sensor or idle control valve?

[poohbah]

This may be completely irrelevant to your GTA issue, but I was watching a car restoration program, in which they were working on mid-2000s Maserati GT3200 V8 coupe.

It had a problem with the drive-by-wire throttle where there was no in-between from no throttle to full throttle. Problem was due to a stupid design flaw, with throttle response determined by a contact scraping over a carbon track. Over time the carbon wore away, so that eventually the throttle response became dangerously erratic. The solution was to replace with a redesigned aftermarket part.

I mention this only because Maserati is obviously part of the Fiat family too, and am wondering if there might be some parts interchangeability with high performance versions like the GTA.

(The TV show I watched was one of the later episodes of Wheeler Dealers - maybe two series ago - if you want to track the footage down).

[festy]

Problem was due to a stupid design flaw, with throttle response determined by a contact scraping over a carbon track. Over time the carbon wore away, so that eventually the throttle response became dangerously erratic. The solution was to replace with a redesigned aftermarket part.

That's how pretty much every throttle position sensor works regardless of brand, they're just plain old potentiometers inside.
Vane-type AFMs use this design too, and they wear out in exactly the same way.

[poohbah]

Cheers Festy. If I recall, they ended up scrapping the original setup on the Maserati and inserting a contactless set-up using magnets to read throttle position.