Accelerator issue, random downshift (auto), ESP off

[Nb VEsv6]

Hey all
I bought a ve sv6 2008.5 with 120,000, now 150,000. It has had these issues the entire time. I have spent many hours searching forums and asking around, I cant find any help for this issue.
I'll explain the issues then what I have done to try and fix.

The ESP comes on at random when driving +10 mins. (Also no cruise control)

When cruising maintaining 80-120km/hr it will randomly downshift from 5th to 4th for 3 seconds then downshift to 3rd (even at 110km/hr) at 4krpm and hold for 5 seconds then back to 5th for 10 seconds then repeat for up to a couple minutes. The only theme I've found is hills increase the chance of this happening, but it happens on flat highway.

When maintaining a speed and not shifting the accelerator pedal it sometimes (once every 20 mins or so) wont register any increased throttle even flat foot it will maintain the current speed forever until I release throttle completely and it fixes immediately.

None of these create an engine code.


I have replaced bank 1 o2 sensors, accelerator pedal, transmission serviced, all new tires, (there were failing cats so i) fitted full system exhaust, extractors, hi flow cats.
Since fitting the extractors it registers an engine code for o2 sensor 1 bank 2 but should not be related since the problems occured before this and havnt changed.

Any ideas would be greatly appreciated as im stumped and spending a lot o money without fixing the issues. Thanks!

 

[lmoengnr]

High flow cats will always cause your Check Engine Light to come on, you'll need some one with tuning software to disable the rear O2 sensors.
You changed the accel. pedal?
Have you cleaned/checked/replaced the throttle body?

 

[Nb VEsv6]

High flow cats will always cause your Check Engine Light to come on, you'll need some one with tuning software to disable the rear O2 sensors.
You changed the accel. pedal?
Have you cleaned/checked/replaced the throttle body?

Hey man, sorry i forgot to mention that i have cleaned and checked the throttle body, and ive had a tuner disable the rear sensors but its the front sensor throwing the code.
Yes ive replaced the pedal which to my knowledge contains the throttle position sensor, this was an attempt to fix the accelerator issue. Thanks for the reply

 

[lmoengnr]

Hey man, sorry i forgot to mention that i have cleaned and checked the throttle body, and ive had a tuner disable the rear sensors but its the front sensor throwing the code.
Yes ive replaced the pedal which to my knowledge contains the throttle position sensor, this was an attempt to fix the accelerator issue. Thanks for the reply

There's also a throttle position sensor in the throttle body.
Have you had the car scanned for codes?
Do you know anyone with a Tech 2? It might pay to drive the car around with the Tech 2 connected to see what it comes up with when the fault happens.

 

[Nb VEsv6]

There's also a throttle position sensor in the throttle body.
Have you had the car scanned for codes?
Do you know anyone with a Tech 2? It might pay to drive the car around with the Tech 2 connected to see what it comes up with when the fault happens.

I did not know about a TPS inside the throttle body, if thats the issue is the fix a replacement throttle body?
I have a cheap scan tool that shows the code that is thrown which is p0151(o2 sensor bank 2 sensor 1). I can remove the code but it shortly returns and there is no other code.
I have 2 videos of these faults occurring, one is the dead acceleration and the other is the downshifting, but theyre too large to post on here.

 

[lmoengnr]

I did not know about a TPS inside the throttle body, if thats the issue is the fix a replacement throttle body?
I have a cheap scan tool that shows the code that is thrown which is p0151(o2 sensor bank 2 sensor 1). I can remove the code but it shortly returns and there is no other code.
I have 2 videos of these faults occurring, one is the dead acceleration and the other is the downshifting, but theyre too large to post on here.

The 2 sensors compare to each other, the sensor in the TB isn't repairable so requires TB replacement.
When you changed the O2 sensor(s?), were they genuine replacements or aftermarket?

 

[Nb VEsv6]

That's good to know, thanks! I'll order a new TB. Fingers crossed that's the problem.
I replaced the o2 sensor that registered the engine code with a OEM sensor, cleared the code and took it for a drive and the code came back on, so put the old o2 sensor back in and used it to replace the other sides o2 sensor incase it was the other side and still registers the same code, leaving me to think that the o2 sensor isn't causing the code, maybe the harness? (the code p0151 registers air mixture pre-cat I think, so related to extractors).
That code (p0151)appeared as soon as the hi flow cats + extractors were put in (3 months ago), it hasn't caused any new troubles that I'm aware of other than the engine light. The accelerator + gear shifting problems have been going for 12 months.

 

[Skylarking]

That code (p0151)appeared as soon as the hi flow cats + extractors were put in (3 months ago), it hasn't caused any new troubles that I'm aware of other than the engine light. The accelerator + gear shifting problems have been going for 12 months.

I would have sorted the accelerator & gear shift issues before spending money on an exhaust system but you are where you are so all issues must be sorted

With the O2 wiring harness, even a cheap wifi/bt OBD scan tools should be able to see live O2 signal data. With such, you should see the voltage sweeping between 0.1V to 0.9V about 5 to 10 times every 10 seconds which would indicate O2 sensor and it’s wiring is OK. But the front O2 sensor readings could still be impacted by pre cat air leaks within the exhaust system since it makes the exhaust gasses lean (and O2 sensor has lower voltage). Such air leaks cause the ECU to pump more fuel into (that bank of) the engine. So check the extractor flange gaskets, pipework and any other gaskets for exhaust leak.

Also, those cheap OBD scan tools are ok for looking at basic engine stuff and clearing engine DTC’s but many won’t look at transmission or other codes nor activate test functions (some can if you pay for the pro version of the apps). So you may not be able to see why the trans is doing what it’s doing... You may have to take it to a dealer to scan.

 

[lout]

throttle position sensor can be replaced without doing whole throttle body
there was an updated tps, not sure when it occurred though
this applies to USA engines, but probably the same

https://static.nhtsa.gov/odi/tsbs/2012/SB-10044229-8347.pdf

 

[Nb VEsv6]

I would have sorted the accelerator & gear shift issues before spending money on an exhaust system but you are where you are so all issues must be sorted

I spent the money on an exhaust system because there was the code p0420 for failed cat, so I figured I would replace the entire system lol. As soon as replacing the system the o2 sensor code replaced the cat code.
I just checked for the voltage on the o2 sensors and found that bank 2 sensor 1 (fault code) has no voltage reading showing (attached pic).
I'll take it back to the guy who fitted the system and ask to look for leaks.

Thanks but i've ordered a new throttle body already.

I have taken it to a transmission shop and asked to have it looked over and serviced and they didn't work it out but pointed me in the direction of a new ECU.