2007 XC70 ECM121B code when below freezing, 30711554 Topic is solved

[EngineeringBloke]

I just was seeing what information I could get from my ETM via my Torque app and an ELM237 adapter in the ODB2 diagnostic port.

I see some small movements reported for the throttle position on turning the key to position 2, but do not see the sweep. That may just happen before the app is talking to the ECU.

The lowest my absolute throttle position reports is 11.4% even with a relative throttle of 0%. I think something is stopping my throttle from closing and the system has recalibrated, but with a bad setting for closed. I see my air to fuel ratio jump up to 28:1 when I am slowing with my foot off the accelerator and it seems to fluctuate between 12 and 15 more than I would expect when 14.7:1 is commanded, I see the measured ratio vary quite a lot. My MPG is typically poor especially for city like driving - 13 mpg.

Is a dirty throttle plate/ETM likely to have this condition? I am hoping to avoid replacing the ETM on my '06 S60.

[XC70Rider]

The nice part of the P2 ETB or ETA is the lack of software intervention via VIDA - so no dealer tax to get the new one done. A $300 part does hurt, but its nice when you nail it and know thats the last time you will see that one.

It costs ~$500 in parts total and a good amount of time but it was worth it. She's accelerating faster and shifting smoother. This code did appear only on cold starts when I purchased it last May. During the warm summer months it ran less lean so the code would appear only once every 2 weeks on cold starts. When it froze up this past winter it was running leaner with the code appearing not only during cold starts but within every mile when it was frigid outside.

I suspected from the beginning it wasn't the MAF because it starts quick and idles smooth. The MAF was one of replaced parts along with new intake gaskets, silicone vacuum hoses, intercooler rubber hoses, upstream O2 sensor, fuel filter, refurbished fuel injectors, and finally the ETM to solve the issue.

Being an Electrical Engineer for 20+ years I know how potentiometers work. I've designed hundreds of PCBs with POTs on them. I tested the resistance and found it was fine with no flickering when it was frozen nor heated. Out of curiosity I may just open up the ETM and feed it some voltage to see how the gears function.

[abscate]

Thanks for making the Brain smarter on P2 throttle bodies. We are just getting into the upside of the failure curve on these, which is good news compared to the 1999 -2001 throttle body.

[mrbrian200]

I remember mentioning in another (old) thread that my sister had a '02 VW Jetta that used this same basic design TB made by Bosch. At 180,000 miles, just before she got rid of the car, I opened the plastic cover on the TB. There was no sign of wear on the gears, they looked brand new, the mechanism was 'tight' with no play in the gears as seen on my Volvo.

The only major internal design difference between the TB on the Jetta and the Volvo was the idle stop mechanism. The TB on the VW didn't have the spring loaded idle stop mechanism - minimum throttle plate position was 'fixed' whereas on the Volvo the throttle plate is designed to 'rest' at around 5-7% open and the ECU can apply reverse current to the stepper motor to close the butterfly all the way if so desired.

I don't think the more complex spring loaded idle stop mechanism is the difference why these TBs wear on the Volvos. My suspicion is the PCV system layout combined with positive pressure on the turbo engines pushes oil (and unknown oil additives) into the TB which softens the gears over time. They're supposed to be relatively immune to oil and most chemicals - but even accelerated wear testing doesn't always faithfully predict what can happen with long term real world exposure.

The PCV design on the Jetta, being a NA engine, never exposed the throttle body to engine oil, and even if it did, there would never be positive pressure across there. Both Volvo (turbo engine) TBs I've had apart showed signs that engine oil had contaminated the internals. The TB on the Jetta (NA) was absolutely dry in there.

Now VW does make a turbocharged engine or two. They are likely to have a similar PCV layout as the Volvos that would subject the TB to engine oil + positive pressure. I suspect with age those turbo VW engines probably have trouble with their TBs also. I remember watching a youtube video where a mechanic had one of these style Bosch TBs off a Ford truck that had failed in this same manner. Though he didn't specifically say, I suspect that truck was a turbo-diesel.

For turbocharged applications these TBs probably need all alloy gears to assure long term reliability. There is one alloy gear in there: on the stepper motor.

[abscate]

Adding my very small numbers to your thesis, MrBrian

My T5 turbo started coding at 125k and pooped the bed at 137k, my parts 1999 NA had a white label ETM manufactured in 1999 with 200k on it still running

Hmmmm

[XC70Rider]

The PO might of adjusted the wastegate rod. The heat shield I removed to access the upstream O2 sensor came off easily. The shield appears to of been previously removed because 1 of the 3 bolts was newer.

When I applied air to the wastegate it moved in a linear fashion. I recall setting the regulator on my 60 gallon Deveilbiss to only 10PSI to get the rod fully open. If the PO adjusted it to open at lower PSI then that's what may of burnt the ETM with only 121k miles.

Is 10PSI the OEM spec for the turbo booster solenoid to open the rod?

[abscate]

The spec calls for a low pressure, of the order of 3-4 psi, to be applied to the wastegate and the rod should just fit on the bracket at that reference pressure.

Most compressor gauges are too inaccurate to do this. I have the IPD gauge if you want to borrow it XC70

[XC70Rider]

The spec calls for a low pressure, of the order of 3-4 psi, to be applied to the wastegate and the rod should just fit on the bracket at that reference pressure.

Most compressor gauges are too inaccurate to do this. I have the IPD gauge if you want to borrow it XC70

After searching I found IPD's tool for adjusting the wastegate rod.



I'll try using the finer regulator & gauge from my paint gun to check if it's set or needs adjusting. Heat shield is still removed so I'll test it again.

[EngineeringBloke]

MrBrian, I appreciate your analysis and experience of the Bosch ETMs.

So with a NA engine, there is vacuum in the ETM from the intake manifold, and there is no obvious source of oil upstream of the ETM (intake, air filter, MAF, tubing). The PCV gases should enter the intake manifold but not via the ETM so they would not get near the ETM gears.

But with our turbo Volvos, oil can leak from the turbo into the boost tube where it is pushed towards the ETM and intake manifold. Inside the ETM there will be positive boost air pressure, at times, which could push oil around the throttle plate pivot and into the container for the gears and thereby could access and affect the plastic gears.

Do you think this (oil pushed into the gears) is enough to cause the effects or do you see a problem with air pressure (boost and fluctuations) causing the throttle plate to vibrate? I think the plate is balanced around the pivot and so this latter mechanism is not clear to me.

I believe in your big thread about engine vibration, you found that there were gaps in the gear teeth, so this was a significant failure that prevented your ECU from setting certain throttle positions.

[mrbrian200]

The whole business I postulated about some sort of air resonance vibrating the butterfly valve I might discount now. The noise I was attributing to this was probably noisy tappets that quieted down as it was no longer idling lean with the new TB. They got even quieter when I switched to a different brand of engine oil (Amsoil S -> Quaker State UD). I can't hear tappet noise at all now unless I'm standing within a couple feet of the front grille or have the hood open. At one point tappet noise was loud enough to hear inside the passenger cabin even with the radio on.

For the record, I still have more vibration felt through the wheel/chassis than should be. I need a round of engine mounts. The mount on the RH side has started making that undeniable clunk between park/reverse/drive. But the vibration is nothing like the coin-op vibrating motel bed the car felt like when the engine was idling lean/before I replaced the TB.