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Old 18-05-2009   #1
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Unhappy Automatic Gearbox Failure!

Hi Guys

I knew this day would come! I think my M Reg Punto has just suffered Automatic Transmission failure.

Any tips or advice would be really helpful. I've read pretty much all the posts which mention similar Automatic Transmission problems, but still can't quite fathom out what's wrong.

Here's the symptoms: The car starts an the engine runs normally. However, when you depress the accelerator pedal the car remains stationary when the gear lever is in either D, L or R. If you rev the engine hard it will creep a little in all of these gears.

So here's what i've tested so far.

1) The Accelerator Micro-Switch.

The micro-switch (which I can only find one of) connected to the accelerator pedal is clicking but not showing continuity when tested with a multimeter when the accelerator pedal is either depressed or un-depressed.

The Haynes manual states that the micro-switch should be closed when the pedal is un-depressed and open when the pedal is depressed. So I obviously have a faulty micro-switch, right!

To test this theory I jumped the micro-switch connector with a paper clip to fool the ECU into thinking the micro-switch was closed, then revved the engine and pulled the paper clip out. Sadly this made no difference in terms of making the clutch engage.

In the Haynes manual on page 7B.3 (Automatic Transmission) Figure 1.1b Electromagnetic Clutch Control System, it shows two switches connected to the accelerator pedal not just one. One is the micro-switch and one is a throttle valve potentiometer. Where can I find the throttle valve potentiometer; could this be blown or broken?

Is the micro-switch essential for the electromagnetic clutch to work? Or does the clutch kick in on engine RPM anyway, even if the micro switch is faulty? Or does the micro-switch have to have a specific resistance which is proportional to the amount of accelerator depression; hence when my paper clip trick failed to work?


2) Electromagnetic Clutch Brushes

I've also checked the electromagnetic brushes and these are fine and not worn any where near their maximum limits. I also checked for continuity through the brushes/clutch windings and found a slightly higher resistance than quoted in the Haynes manual, but this is to be expected since the brushes would cause a higher resistance anyway, being made of carbon/copper.

3) Automatic Transmission Fuse

I've also checked the 15A Automatic Transmission fuse under the bonnet and this isn't blown.


So is it a simple micro-switch replacement that I need or a new/re-con electromagnetic clutch? If the micro-switch is causing this why doesn’t jumping the connector fool the ECU?
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Last edited by RudeBwoy; 18-05-2009 at 23:07.
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Old 24-05-2009   #2
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Re: Automatic Gearbox Failure!

Thanks for all your help, not! Problem solved and it didn't cost a single penny, just a lot of hard work!
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Old 24-05-2009   #3
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Re: Automatic Gearbox Failure!

Sounds like you've covered everything, and obviously have resolved it. What was it in the end? Sympathising with anyone with gearbox/clutch issues, my gearbox is going in my Punto as well (manual though).
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