EPC problem in 4th Gear

[hawleybeach]

I have a Polo, 5sp Manual, that can no longer be driven in 4th Gear because the EPC light comes on in that gear, and fuel can be momentarily cut to the motor at low throttle and low rpm. (That is very ugly when you are driving, nasty banging noises through the drivetrain)

To show the problem, I can park the Polo with the motor running and clutch depressed

In 1st Gear, the Engine Idles at 650rpm
In 2nd Gear, the Engine Idles at 650rpm
In 3rd Gear, the Engine Idles at 650rpm
In 4th Gear, the EPC light comes on and the motor runs very roughly as fuel (or spark or both) is momentarily stopped. The rev counter can be seen momentarily dipping

Also, the Stop/Start system then goes into error, and will not activate for typically 10 minutes

[iichel]

The next logical step would be to read any errors stored in the error memory of the car and see why it's not happy with 4th gear.
What about 5th and perhaps 6th?

[hawleybeach]

5th Gear has no problems. Note that it is only a 5 speed Gearbox . (The 105PS motor gets the six speed manual box)

[RUM4MO]

Have you ever considered checking the wiring to the gearbox "position/gear" sensor(s)?

[iichel]

Gearbox doesn't have such a sensor

[amer6R]

Tg uses wheel speed and revs to calculate in witch gear you are in

[mikerj]

I'd check to see if the linkage is rubbing against any cables. It makes no sense for this to happen when stationary otherwise.

[RUM4MO]

The 6C version of Polo, at least my wife's 2015 1.2TSI 110PS, I'm sure, has a gearbox "gear selected" system and does not derive which gear it is in from engine speed and road speed as earlier models did.

[Dink]

The 6C version of Polo, at least my wife's 2015 1.2TSI 110PS, I'm sure, has a gearbox "gear selected" system and does not derive which gear it is in from engine speed and road speed as earlier models did.

still the same. was getting clutch slip in my gti and when it did the gear selected also changed

[hawleybeach]

Actually a couple of the replies here nailed the problem

The last time I got my Polo serviced I demonstrated the problem to my mechanic. He found that the manual gear selector did actually have a component that was rubbing against a wiring harness in 4th gear. The insulation had actually worn away from a purple wire, and it was earthing out, hence the strange EPC problems. Wiring has been taped up, wiring harness has been cable tied up out of the way, and problems solved

Polo is 6 years old and has done about 120,000km. During this service, spark plugs required changing and a couple of the "Coil over Plugs" had slightly melted in position, so broke coming out. From memory the plugs weren't actually replaced at 60,000km because there were none in stock in Tasmania, so replacing them got forgotten about, so the most of the "Coils over Plugs" had not been removed before (could have been a factor)

Next service can fix the slight water leak around the thermostat housing, unless it becomes more serious before then. Apparently that is also a common problem for Polos

I used to have a V6 Camry. It had done 400,000km when I sold it, and the only thing that went wrong was the Car Battery died and a few sets of front brake pads. Didn't use any oil, and the Spark Plugs had done 200,000km

[hawleybeach]

Actually a couple of the replies here nailed the problem

The last time I got my Polo serviced I demonstrated the problem to my mechanic. He found that the manual gear selector did actually have a component that was rubbing against a wiring harness in 4th gear. The insulation had actually worn away from a purple wire, and it was earthing out, hence the strange EPC problems. Wiring has been taped up, wiring harness has been cable tied up out of the way, and problems solved

Polo is 6 years old and has done about 120,000km. During this service, spark plugs required changing and a couple of the "Coil over Plugs" had slightly melted in position, so broke coming out. From memory the plugs weren't actually replaced at 60,000km because there were none in stock in Tasmania, so replacing them got forgotten about, so the most of the "Coils over Plugs" had not been removed before (could have been a factor)

Next service can fix the slight water leak around the thermostat housing, unless it becomes more serious before then. Apparently that is also a common problem for Polos

I used to have a V6 Camry. It had done 400,000km when I sold it, and the only thing that went wrong was the Car Battery died and a few sets of front brake pads. Didn't use any oil, and the Spark Plugs had done 200,000km

[RUM4MO]

Good result there!

Coil On Plug (COP), yes, if they don't get removed for a very long time, they can be very difficult to get off the spark plugs, there was a Japan based member on here with an old 9N Polo, and he had to make up a steel puller to force the coils up off his plugs as they had not been off for a very long time!

[hawleybeach]

I'd check to see if the linkage is rubbing against any cables. It makes no sense for this to happen when stationary otherwise.

Mike was spot on. Part of gear selector, below gear lever was rubbing against wiring in 4th gear. Had worn through insulation and was shorting out a purple wire

[hawleybeach]

The next logical step would be to read any errors stored in the error memory of the car and see why it's not happy with 4th gear.
What about 5th and perhaps 6th?

First thing to do with any problem is to physically inspect what is going on. Error codes are never going to tell you that putting the gear level in 4th gear is shorting out a wire because the insulation has worn away