After 12 hours of 80mph interstate driving, the car went into limp home mode & rough running. Pulled to side, turned off & restarted fine. Accelerates & cruises great but I noticed that if I'm cruising at 80mph, take foot from accelerator for a few seconds, then try to rapidly accelerate back to 80, there is a noticeable hesitation/jerk, then runs fine. If I accelerate somewhat slower, I don't notice the hesitation. Any idea what is causing this? Fuel pump replaced 2 years ago, with fuel filter, PC system replaced last summer. Running 91 octane fuel.Thanks.
Marlin

Do you have access to VIDA-DiCE? I got along fine with a generic code reader with my 2000 V70, but after buying 2004 and 2006 XC70s, it became clear I needed something that would read proprietary codes and allow resetting of modules, etc.

That said, I am wondering if this is PEM (analogous to the older fuel system relays, only more complicated and expensive). I keep a spare from a pick and pull in each car, as well as a spare MAF and a couple coil packs.

The PEM is either in the spare tire well on the passenger side, or on top of the gas tank. There is a relocation harness to move it from the gas tank to the tire well. If you buy a used one, get one that was from inside. New ones are quite expensive-- $250 or so. Used ones can be found on ebay.

Good luck!

I have looked at the area around the fuel filter on my car's plastic tank & looked in the spare tire well, but don't see a PEM. Was a PEM on all 2004 cars? This one was purchased in Washington state. Thanks.
Marlin

PEM for V70 started in 2005, as far as I know.
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Keeping it running is better than buying new

If I go to the dealer, can they determine which component triggered the code? Does paying the diagnostic fee usually also include any software updates?

I bought a used Volvo DICE clone used locally, and downloaded a new repack of the software VIDA that runs on my WIN10 laptop-- $60 to get the whole thing running, less than having codes read once at a shop. Something worth considering if you are planning on keeping your car. It allows you to read and reset SRS codes and set user parameters on things like seat heater temperatures, etc. You will need a subscription for software for things like keys and module reprogramming, you can buy a 3 day subscription, but you need to know what you're doing with reprogramming modules.

Good luck!

You might also want to check the grounds connection if you can get an electrical diagram.

The pins at the ECU have a tendency to get out of alignment you need a special tool to unlock the tabs.

No and never. Dealers are like everyone else, they are in the business to make money.

It may be possible to rule out one or more of the causes, but my bet is with the throttle body. Remember, dealers do not "repair", they 'replace' components. Will they clean the throttle body or the throttle position switch? Probably not. They will never clean the MAF, replace only.

Is your air filter clean? You could pull the MAF and do a visual on it or get some MAF cleaner and spray it. Pulling the throttle body and cleaning everything you can may be satisfying.

This is a 17 year old car and might have 17 years of grime.

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Keeping it running is better than buying new

Happened again, twice in 4 hours of interstate driving. Triggered CEL. This time “ecm internal fault”. Haven’t been home to clean throttle body. Think it’s still the Throttle body or should I start looking elsewhere?

ECM fault is tricky. I remember some people reporting that the contacts at the bottom of the ECM needed cleaning. The hard part is getting the proper tool to release the ECM from the box before cleaning the contacts with alcohol. There might be a Youtube for that. Battery MUST be disconnected for at least 15 minutes prior to removal.

Cleaning the throttle body is always a 'good' suggestion. Getting the 4 bolts off is not easy, but cleaning the butterfly is always satisfying! Especially now when the weather warmer.


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Keeping it running is better than buying new

I noticed that the problem was occurring every 2 hours on the first 6 hours of the trip so for the next 12 hours I made sure I stopped & started the car at least once every 1-3/4 hours & it never happened again.

It's too bad you didn't pull the codes. It might not be too late to scan for any 'pending' codes.

How is the throttle body? Clean? And the throttle position switch?

Driving at a constant 80mph is good for the engine, cleans the valves etc.
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Keeping it running is better than buying new

Only code now is ECM-981A. ECM internal fault.

This is cute:

https://www.dtcdecode.com/Volvo/ECM-981A
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Keeping it running is better than buying new