[muz]

The car is a 2010 i30 2.0 liter automatic, approximately 95000kms.

We bought this car second hand for my daughter and it has been great, however we now seem to have some major issues with the car.  It seems like a transmission slip.

If the car is under moderate load, for example going up a hill or accelerating out of a corner the card will shudder and vibrate (very loud), it almost seems like a loss of power.  The engine will then rev high and the transmission seems like it is slipping and/or hunting for a gear, this is then followed by a very load thud and the transmission engages and the car continues on.

This is reproduce-able at will  and occurs at any operating temperature or ambient temperature.  At times the auto seems hesitant to change, quite evident if you accelerate hard.

What is really strange is that it happens more frequently when the fuel tank is below half (go figure!).

The car has been to the dealer and extensively tested (I thought it was a valve body issue), the senior technician was very helpful and he felt it was not a valve body issue or a transmission issue but rather an ecu issue.  He performed an adaptive reset which seemed to help but not resolve the issue.

The car has subsequently been sent to an auto electrician that specializes in ecu diagnostics.  They were able to re-produce the issue with the diagnostic gear attached and no ecu fault was recorded.

During this entire time there have been no fault codes recorded.

Of recent times it has been shuddering each time when driving up hill and not kicking down, it over revs at this time.

Today, I get a panic phone call from my daughter on her way to college that the car misbehaved badly. Whilst driving up a hill it started to shudder followed by a violent bang and a loss of power. It appeared that the transmission would not change past 3rd and was very sluggish.  After this happened it was extremely sluggish moving off from a standstill.  She managed to get to college okay. 

We prepared for possible tow home as it sounded bad however the car performed without fault and in fact seemed somewhat better!

I'm at a loss as to what is going on.  A couple of questions come to mind:-

1) I have read that there are poor solder joints on the solenoid harness.  Is this harness external to the auto, can I repair/re-solder these joints.

2) Given that it's worse when the fuel tank is below half could it be a bad fuel pump/clogged filter causing a drop in fuel pressure and ultimately causing a loss of power and ecu confusion?  I have seen an internal fuel pump before with damaged hoses causing issues below half full.

Any other thoughts or opinions would be greatly appreciated as I'm at a loss.

[tw2005]

Welcome.

I hope you stick around longer and provide better feedback than a number of recent new arrivals asking for help.

Paragraph 3.

Strongly suggests to me this is a transmission issue.

Is the  dealer and whose  very helpful senior technician  who extensively tested the transmission the same people that sold the car and have any liability for warranty repair?

Also the latter paragraph also sounds like transmission fault, and gone into failsafe, generally third.

I have been in one of these when it does this at highway speed and there was a jolt and RPM increase. that's because whenit does this there is no electronic control and the box simply dumps into third.  Tryin to take off in third will seem like no power.

2nd will be available by manually selecting with the shifter and reverse. No electronic controls will take place.

I'd say when the car shutdown the ECU reset and transmission then functioned again. I'd also expect a code stored if it went failsafe too but it may be one that clears.

You may have to find a good independent to check it and get a report if you have wty difficulties .

[Dazzler]

Welcome. I can't really help but must commend you on the excellent 1st post. Very well explained and your thought patterns are logical too.

It does sound very much like the transmission to me, but cant explain why the fuel level is haaving a bearing. 

[muz]

Thanks for your helpful comments.

The car was purchased from a second hand car dealer and not Hyundai.  The statutory warranty on second hand cars is only 3 months in Australia and is well beyond that.

I really hate intermittent faults, I drove the car today and it performed without fault.

[tw2005]

Thanks for your helpful comments.

The car was purchased from a second hand car dealer and not Hyundai.  The statutory warranty on second hand cars is only 3 months in Australia and is well beyond that.

I really hate intermittent faults, I drove the car today and it performed without fault.

Yes, don't we all. Any chance you have an OBD2 scantool?

[muz]

I don't gave a scan tool handy but I have access to one.  I have checked for fault codes previously and none have been recorded.

PS.  I love the functionality of this blog!

[tw2005]

Have you read this one?

Transmission Valve Body Fault - Need Advice

Cruiserfied is a qualified and HYundai Tech

He mentions not seeing DTCs or limp with bad  Valve Body.

Be careful.
I have seen enough A4CF2 valvebodys start playing up. What i have never seen from the "common" valvebody symptoms is limp mode or DTC's.

Did they mention any testing on the solenoid at all? Because if there is a code for solenoid malfunction they should have carried out diagnosis on the solenoid. And for the record a malfunctioning valvebody cannot set that code.
It will be either the solenoid circuit, solenoid itself or the PCM.

As I write this , if there's no DTC and it does sound like limp, how does it know to go to limp because the trigger would be an event which a DTC should be present.

Only thing I can think is the VB is the fault and the solenoids are functioning but the mechanic or internals of the VB are fouling or jamming i.e the valving and bores?

Tough one. a VB is a grand at least plus install. Used box that may be ok, probably more and more labour.

at least a VB can be done with box in the car.

[muz]

Thanks tw2005! That's an interesting post and quite achievable at home.  I think it's well worth the look, nothing ventured nothing gained.

[tw2005]

Thanks tw2005! That's an interesting post and quite achievable at home.  I think it's well worth the look, nothing ventured nothing gained.

keep in mind I'm not saying it's harness, just a handy insight.

Things to have in mind.

Correct fluid, SP3 which is a Mitsubishi spec, I'm running a Full synthetic Penrite Multi in mine but original would have been SP3

I don't know about Hyundai dealers selling it as my local does not but Mitsubishi may still sell SP3 in 5L bottles and was cheaper than aftermarket 4L bottles of multi vehicle. That was 2 years ago

If the pan has never been off, it's liquid sealant, Threebond 1281 is a good choice( not cheap but excellent )

in lb torque wrench will be needed

[eye30]

As you mentioned re fuel level then why not check out fuel pump and filter.

I had an Accent and the pump was faulty  so when i went up an fair incline the car would struggle but on the flat or down it rain smooth.

Worth a look just to rule it out before shelling out for transmission checks etc