Hyundai Forums banner
1 - 11 of 11 Posts

·
Registered
Joined
·
83 Posts
Discussion Starter · #1 ·
Hi All. Just wondering what to do next.

My Sonata is reliably going into limp mode when it's cold, but once it has been running for 15mins or so, I can switch off the ignition, wait a minute, and then start again and it runs fine and doesn't go into limp mode while the car remains warm. Additionally, when the car is cold, I can start it and it will generally continue to idle, but if I try to drive off, the moment I back off the accelerator pedal just the slightest, it stalls. When moving the accelerator pedal while the car is cold (i.e. for the first 5mins), it's as if it's "all or nothing" - I can't seem to transition gently between acceleration/cruising and deceleration. It continuously throws P0340 codes (Cam sensor circuit). Can a P0340 cause the tranny to go into limp mode when the car is cold? Tachometer only works intermittently, but seems uncorrelated with the symptoms.

This is what I've done in the last 500kms trying to fix the problem:
  • Replaced Crank & Cam sensors;
  • Swapped ignition coils, MAF sensor (and cleaned it), and EFI pressure regulator with my other identical car (which is running fine);
  • Replaced fuel filter;
  • Replaced throttle position sensor;
  • Replaced IAT sensor;
  • Replaced IAC regulator;
  • Replaced ECT sensor;
  • Tested Cam sensor connector for 12 & 5V consistency from ECM;
  • Replaced the Tranny speed input sensor & connector.
Any suggestion on what I can look for next? I'm wondering if maybe the ECM is on it's way out? How could I check that? The car has done ~240,000 kms, seems to have good compression and doesn't burn/leak/use any oil.

Thanks in advance.
 

·
Registered
Drives : Nissan NV200 Flies : Rans S6ES
Joined
·
16,785 Posts
Any suggestion on what I can look for next?
Have you checked that the temperature sensors are showing plausible values on the scan tool data list? Before the first start of the day the temperatures in the engine should all roughly equal the ambient air temperature.

Also take a look at the fuel system status. Does the problem clear as soon as the fuel system switches to closed loop control?

You might want to take a look at the O2 sensor output voltages too to see what is happening with the A:F mixture when the engine wont respond to the throttle, and when it stalls.

If I helped you fix it, why not...

Your support is greatly appreciated
 

·
Registered
Joined
·
83 Posts
Discussion Starter · #3 ·
Have you checked that the temperature sensors are showing plausible values on the scan tool data list? Before the first start of the day the temperatures in the engine should all roughly equal the ambient air temperature.
Thanks for the tip. Will do :)


Also take a look at the fuel system status. Does the problem clear as soon as the fuel system switches to closed loop control?
Forgive my ignorance but I'm not familiar with this. Can you point me to an explanation somewhere so I can understand what you're asking here? Many thanks :).


You might want to take a look at the O2 sensor output voltages too to see what is happening with the A:F mixture when the engine wont respond to the throttle, and when it stalls.
OK thanks. I take it I can just do that with the code reader plugged in and active when I start the car? Or is it done some other way?

Thanks again - much appreciated :)
 

·
Registered
Joined
·
83 Posts
Discussion Starter · #4 ·
Update @AUTOSPARK:
Air temp sensors...
Were all within expected parameters (i.e. at ambient air temp for cold start then correspondingly increasing as the engine warmed up).

O2 Sensors...
With ignition on, 02 sensor 1 = 0v, O2 sensor 2 = 1.22v.
On cold start and then throughout the 30min drive I took the car for, sensor 1 remained at 0v while sensor 2 fluctuated rapidly between 0.02v-1.22v.

I'm pretty sure my car only has 1x pre and 1x post cat 02 sensor, from memory.

Fuel system status - not sure how to check this (my car is pre-OBD2 so readings are a little limited).

Interestingly, on this occasion, I stopped after 15mins (as usual) and switched off the ignition to reset the tranny out of limp mode, which it did as predicted, but just as I was on the home stretch (last km before turning into my street & driveway), the tranny thumped back into limp mode while I was cruising along at 80kph (i.e. jumping from 4th gear ~1700rpm into third/limp @~2300rpm).

Would those 02 sensor readings cause the crappy cold engine runs and/or tranny limp mode?
 

·
Registered
Drives : Nissan NV200 Flies : Rans S6ES
Joined
·
16,785 Posts
On cold start and then throughout the 30min drive I took the car for, sensor 1 remained at 0v while sensor 2 fluctuated rapidly between 0.02v-1.22v.
That doesn't sound right. Was the engine running normally towards the end of the 30min drive?

jasper180268 said:
I'm pretty sure my car only has 1x pre and 1x post cat 02 sensor, from memory.
On a V6 engine there are normally 4 sensors. 2 for each bank of cylinders.
If your car is pre-OBD2 it might only have two sensors. One for each bank of cylinders, located up stream of the cats.
If that's the setup on your engine it sounds like one bank of cylinders is running very lean. Or one of the O2 sensors has failed.

jasper180268 said:
Would those 02 sensor readings cause the crappy cold engine runs and/or tranny limp mode?
I doubt the O2 sensor readings themselves would cause crappy cold engine runs because the O2 sensor don't really do anything when the engine is cold (during open loop control). But they might be providing a clue about where the problem with the engine lies.

The tranny dropping into limp mode is probably a tranny issue and unrelated to the crappy cold running. You'll probably need to have the transmission module scanned to see what trouble code is being logged to figure out what is causing that problem.

If I helped you fix it, why not...

Your support is greatly appreciated
 

·
Registered
Joined
·
83 Posts
Discussion Starter · #6 · (Edited)
That doesn't sound right. Was the engine running normally towards the end of the 30min drive?
Yes, once it warmed up, it always runs quite smoothly, so jumping back into limp mode in this instance was quite a surprise. Not as even and gutsy as a new car, but smoothly enough, even though acceleration is slightly uneven at times (but passengers never notice it).

On a V6 engine there are normally 4 sensors. 2 for each bank of cylinders.
If your car is pre-OBD2 it might only have two sensors. One for each bank of cylinders, located up stream of the cats.
If that's the setup on your engine it sounds like one bank of cylinders is running very lean. Or one of the O2 sensors has failed.
Yeah I remember having this conversation once before in a forum somewhere when I had to change the pre-cat O2 sensor in my 2001 EF-B 2.7L V6. Everyone kept telling me that, until someone else from Australia (a mechanic) joined in the conversation and clarified that the Australian models only have one pre and one post cat O2 sensor. I don't know why they did it differently for the Oz models - especially when they're fully imported anyway... I have looked at the sensors on my 1998&9 EF 2.5 V6s yet but I'm assuming they're likely the same. The only wiring I can see in the area where I'd expect a bank 1 (exhaust) O2 sensor to be is that which goes to the crank sensor further below (hence my assumption that it's likely the same as my EF-B 2.7). I'm wondering if the 0v registering may be because there isn't one.... unless one is for the pre-cat and the other for the post-cat? Interesting nonetheless - I'll have a look at the sensor next time the opportunity arises and maybe pop a new one in anyway just to see what difference it makes.

I doubt the O2 sensor readings themselves would cause crappy cold engine runs because the O2 sensor don't really do anything when the engine is cold (during open loop control). But they might be providing a clue about where the problem with the engine lies.
Possibly not anymore... I picked a brand new MAF sensor fairly cheaply so I thought I'd try that anyway - and I did a throttle body clean while I was at it (not that it looked like it needed it though). Engine runs very nicely now, even when cold :-o. I don't get why this is the case because I swapped the original MAF sensor with my other EF 2.5 and it didn't make any difference to either car :unsure:. Anyway, that seems to be the engine run side of things sorted for now (unless the cheap new MAF sensor's lifespan matches the price I paid for it...).

If nothing else, this little episode has brought my attention to the possibility that one or both (or more?) of the 02 sensors might not be in the best shape, so I'll certainly be keeping an eye on them over the coming weeks/months...


The tranny dropping into limp mode is probably a tranny issue and unrelated to the crappy cold running. You'll probably need to have the transmission module scanned to see what trouble code is being logged to figure out what is causing that problem.
Yes, that certainly seems the logical conclusion now. Unfortunately I can't read the tranny codes so will need to take it to a transmission place and see what they say. I took it once before when the engine was running fine but it was dropping into limp mode occasionally (my local auto parts shop had read the codes before and said the solenoids were gone), but they said it was a circuit issue and pointed to a dodgy speed input sensor connector. So I replaced the connector, and the tranny behaved perfectly for a few weeks before the engine started having these problems and then a short time later the tranny started going into limp mode again and the p0340 code appeared. And that's where this thread started ....

One problem seems to be sorted and the other logically seems to be isolated to the tranny, so onto that mystery now :).

Mind you, I still don't understand how I got a P0340 code if the MAF sensor was the problem.... :unsure:
 

·
Registered
Joined
·
83 Posts
Discussion Starter · #7 ·
Update: P0340 code is back again, and also now P0134 (O2 sensor), which is not surprising given Autospark's reference to 02 possibilities... Can't work out what's triggering the P0340 code though - connector signal from ECM checks out ok and sensor is brand new...

Sigh....
 

·
Registered
Drives : Nissan NV200 Flies : Rans S6ES
Joined
·
16,785 Posts
Can't work out what's triggering the P0340 code though
You'd probably need to have a look at the cam & crank sensor signals on an oscilloscope then compare your scope trace to a known good trace from the shop manual to figure out what is going on. But that's not something most garages would even be able to do. That's what keeps guys like me in a job :).

If I helped you fix it, why not...

Your support is greatly appreciated
 

·
Registered
Joined
·
666 Posts
What's the voltage on the battery with engine running?
On one of my other cars, I had the alternator going bad (later I found shorted diodes in the bridge). That was leading to about 13V on battery and probably was pushing a lot of AC garbage currents on the power lines.
That affected my camshaft sensor reading, getting P0340.
Once I replaced the alternator, and had a clean 14.2V on battery, the P0340 never appeared.

Temperature can affect a worn-out alternator output by mechanical dilatation of brush springs, etc...
 

·
Registered
Drives : Nissan NV200 Flies : Rans S6ES
Joined
·
16,785 Posts
That was leading to about 13V on battery and probably was pushing a lot of AC garbage currents on the power lines.
That affected my camshaft sensor reading, getting P0340.
This is a good point. You could try measuring the AC voltage across the battery terminals with the engine running to see if an alternator fault might be the cause of the P0340 code. Ideally there shouldn't be any AC voltage, but I think your allowed upto 50mV (0.05V AC).

If I helped you fix it, why not...

Your support is greatly appreciated
 

·
Registered
Joined
·
83 Posts
Discussion Starter · #11 ·
What's the voltage on the battery with engine running?
On one of my other cars, I had the alternator going bad (later I found shorted diodes in the bridge). That was leading to about 13V on battery and probably was pushing a lot of AC garbage currents on the power lines.
That affected my camshaft sensor reading, getting P0340.
Once I replaced the alternator, and had a clean 14.2V on battery, the P0340 never appeared.

Temperature can affect a worn-out alternator output by mechanical dilatation of brush springs, etc...
Many thanks. That could actually make sense in this instance. I've been getting the feeling maybe my battery was nearing the end of it's life (sometimes it sounds like it's struggling a bit), but perhaps it could be the alternator... No warning lights or anything else to suggest alternator is the issue, but might not quite be enough to trigger that while still causing probs for the cam sensor. When I last looked at the voltages while running, it didn't look overly concerning, but I think there were stages where it was down around 13v instead of up near 14v so you could indeed have hit the nail on the head. Will have another look this weekend and see what comes of it. Might just swap the alternator with my other car and see if that makes a difference....

Thanks again :)
 
1 - 11 of 11 Posts
Top