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C70 ECM electrical puzzler

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Re: C70 ECM electrical puzzler

Post by PeteB » Mon Jul 10, 2017 7:03 pm

Debug the battery drain, as others have mentioned it might lead to the source
of your troubles. Have you checked the grounds?



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Re: C70 ECM electrical puzzler

Post by sleddriver » Sun Aug 06, 2017 10:55 am

Any updates from the OP?


1998 V70 T5 222,230 miles. Original Owner.

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Re: C70 ECM electrical puzzler

Post by RexxWonder » Wed Oct 11, 2017 10:17 am

Hello all,

It has been some time yet and I am still trying to solve this puzzle. I have all new information now:

Over time I have replaced most every possible issue that came up in the Diagnostics report (VIDA). Today I finally reached a point where there are no error codes either when I first start the car, nor when it starts to exhibit the issues (which it still does). So to recap where I am now:
-C70 will start first time after sitting overnight
-It will run perfectly (and can even be turned off and restarted) until it is within about 20 degrees of median operating temp
-*At this point it will sputter and bog as though the timing is waaay off, but ONLY below about 1800 RPM (if I can rev it above 1800, it will run and rev fine).
-Once I turn it off, it will not start again until the next day.

***repairs done***
-Replaced Cam Position Sensor, Crank Sensor (RPM), CVVT Sensor, Fuel Pump
-Ohmed-out all sensor wires to the baseplate (all good)
-Replaced the Alternator (shorted)

I am at a complete loss here. There is nothing logical about this. There is something that seems to cause the rough running and lack of start but I am getting NO fault codes...NONE!

Could this have anything to do with the Throttle Module? Software upgrade? Maybe the Accelerator signal? It is so bizarre because it runs perfectly when cold, and then even when it warms it will run well above the 1800 RPM mark (though it will never start again once it warms and I turn it off). How can a car be so maddening...there is nothing that will direct me to the source of the problem...it seems that it is all innuendo and inference with trial-and-error being the only path to solution. Is this really the Volvo experience? I have an Audi A6 Twin-Turbo that will tell me exactly what is wrong at any given moment. WTF, Swedes?

Any helpful thoughts are welcomed.


Current stable:
-2002 Volvo C70 convertible, 2.3T, 5-speed manual (73,000 Miles)
-2001 Audi A6 S-Line 2.7 twin Turbo (upgraded to K04s), 6-speed manual (230,000 miles)
-1970 GTO convertible: rebuilt toy with 400 (416 CID) and TH400

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Re: C70 ECM electrical puzzler

Post by volvooh » Thu Oct 12, 2017 7:24 am

I'd really look at your ECM. Had very similar issues before I replaced mine. The ECM was literally shutting off shortly after the car reached normal operating temperature. I sent it to ARD and they reported signs over overheating in the original ECM.

Its super easy to remove, and in comparison to other components you replaced, not that expensive. Donor ECU and cloning ran about $150.00.



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Re: C70 ECM electrical puzzler

Post by RexxWonder » Thu Oct 12, 2017 8:43 am

Perfect. Thanks, Volvooh. That has been my contention all along, but I had so many tell me that the LAST place I should look was the ECU. It has been a long strange trip, but I talked to ARD last night and am sending all out this morning. Thanks so much for your input and I have my fingers crossed this gets it.
It's convertible weather!!


Current stable:
-2002 Volvo C70 convertible, 2.3T, 5-speed manual (73,000 Miles)
-2001 Audi A6 S-Line 2.7 twin Turbo (upgraded to K04s), 6-speed manual (230,000 miles)
-1970 GTO convertible: rebuilt toy with 400 (416 CID) and TH400

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Re: C70 ECM electrical puzzler

Post by abscate » Thu Oct 12, 2017 1:09 pm

IT is the last place you look as ECM failures are so rare. For everyone solved by an ECM flash we probably have 500 with other problems, who then get frustrated at throwing parts/money

VolvoOH went through stepwise diagnostics to eliminate everything but the ECM


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Re: C70 ECM electrical puzzler

Post by volvooh » Fri Oct 13, 2017 7:43 am

x2 on what Abscate says. Even ARD said the same thing- its just so unusual for the ECM to go bad, but in my case it did. Honestly even when I got it back and running it was a long time before I was confident with the car again, just because the instance of failure was so low. But if you've eliminated all the other possibilities, its probably worth trying.



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Re: C70 ECM electrical puzzler

Post by wizechatmgr » Sat Oct 14, 2017 10:17 pm

It is possible that when the alternator went it spiked the ECU. I would say most alternator failures don't end up with voltage way over spec - but it could happen.

I know when my alternator went it took out both fog lights and both headlights that were on at the time. Those shunting until blowing likely saved my ECU. This is the only time I've had an alternator fail in this way. All others just stopped having output or the bearing started groaning.


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Re: C70 ECM electrical puzzler

Post by precopster » Sun Oct 15, 2017 2:45 am

Just replaced a bad Bosch ECM on our 2002 XC70. Due to the age of these computers and the thousands of heat-up/cool-down cycles they perform in a lifetime the likelihood is getting higher as these cars age. Mine was also shutting engine down with no relevant codes and restarting immediately with no issues.

I did get a ECM communication code once only.


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Re: C70 ECM electrical puzzler

Post by sleddriver » Fri Oct 20, 2017 6:44 pm

RexxWonder wrote:
Thu Oct 12, 2017 8:43 am
Perfect. Thanks, Volvooh. That has been my contention all along, but I had so many tell me that the LAST place I should look was the ECU. It has been a long strange trip, but I talked to ARD last night and am sending all out this morning. Thanks so much for your input and I have my fingers crossed this gets it.
It's convertible weather!!
Hey Rexx...did it work?


1998 V70 T5 222,230 miles. Original Owner.

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