Battery Disconnected - First CCM NO Power, Then Rough Idle

[jderosa3]

I have been ripping my hair out lately with my wife's 2001 XC70 Turbo. This post is mainly about my recent battery disconnect issue, but want to explain what I have done.

This car has had rough idle issues for some time and dimming dash lights so a couple weeks ago. I had taken out the ETM and cleaned it as well as replacing the PCV system components. I also replaced the alternator. Seemed like all the right things to do while I was in their with the intake manifold out of the way.

During this first repair I didn't have the battery disconnected. Car drove perfect for a few weeks. Then a few days ago my wife calls me on her way to work and the car went into "limp" mode. Not going above a certain speed. Rough idle.

It seemed to only be happening in the hot weather. However, this problem was intermittent. To try and correct this, at least just to see if disconnecting the batter would reset something in the ECU to get things "re-learned" - I disconnected the battery, but when hooking it back up did not follow the procedure to reconnect the battery on these models properly (I didn't realize there was one at this time).

When I powered the car back up everything was fine with the exception of the Climate Control dash area had no power, but the car drove fine.

This morning I researched and found where you have to drain the system of electrical power and reconnect the battery with the ignition in the "II" position. Well this fixed the Climate control power issues. But now the car seems to be in permanent limp mode.

What is going on here??? :twisted:

I have a rebuilt ETM that I am willing to throw in - I had purchased it because of a P0121 code I pulled when the car was initially idling rough (I also got a new MAF sensor I want to throw in as well), but want to understand now why after this batter disconnect it made the throttle act this way and put the car in this mode.

Could the ETM just coincidentally kicked the bucket during this, or is the computer reset causing this. I am so lost here. Can anyone offer some advice about what I might be experiencing. I appreciate any help one can provide - I am mentally preparing I might have to tear into this thing again today.

[hoonk]

This car has had rough idle issues for some time
I had taken out the ETM and cleaned it as well as replacing the PCV system components.
Drove perfect for few weeks
Then car went into "limp" mode. Not going above a certain speed. Rough idle.

now the car seems to be in permanent limp mode.



Sounds like a bad throttle, how old is the one on the car? Unless you created air leaks working on the Throttle or PCV system.

[howardc64]

Sounds like whatever was acting up to trigger limp home started before you did the power reset. P0121 code points to TPS so your ETM is likely the culprit.

If you can locate a Volvo diag tool (VIDA/DiCE) owner (post your region and see if anyone nearby), this tool has an ETM sweep test which rotates the throttle plate and read+compare value of both TPS to evaluate accuracy.

I did a DIY TPS repair awhile back and had the ETM connected/disconnected quite a bit without mounting it onto intake manifold. I recall the ETM does a quick self calibration (TPS angle recalibration) for a couple of seconds when it first sees power (you'll hear this) So maybe your power interruptions could have caused it to see bad recal due to worn TPS. You can do the following quick test... Disconnect ETM's power at the plug mounted on the subframe. No need to disconnect battery. Just unplug, wait a few min, replug and switch key to position II to hear the recal. See if the limp home goes away.

In any case, likely need an ETM with good TPS.

[Astro14]

First - disconnecting the battery in this car does nothing to change performance. The ECM "learns" and stores those adaptations. So, the trick that worked on late 80's cars with no memory storage won't work here.

Next, reconnecting the battery initiates a computer reboot. Do it right and it will reboot correctly. Read Howard's site.

Finally, all that work likely has nothing to do with the drivability issue now. Correlation is not causality.

It could be your ETM, it could be your MAF.

Start with the basics - when you put his back together, did you get everything back on right? Intercooler hose to ETM? ETM control wiring? Turbo boost hose over the engine?

[jderosa3]

Guys, Thanks for all the advice. I ordered a ETM that was rebuilt in 2013 and it seems to be working fine. Did a direct swap and all is well! No need to reset anything. Something happened when I disconnected the battery because it was in permanent limp mode. Before it only happened once or twice.