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Discussion Starter · #1 · (Edited)
HI guys, I just completed replacing a few engine mounts on our 2008 xc70 3.2 Awd.
I had to remove the battery to access the engine mount supporting the transmission located under the battery tray.
Also I replaced the fuel pressure sensor on the fuel rail. This involved releasing pressure on the high pressure valve (passenger side) and removing/replacing the sensor (left).
The high pressure valve plastic cap's threads stripped upon reinstall. ( i have a new valve on order).
The car was running fine before despite engine vibration and a periodic check engine for the fuel pressure sensor. VidaDice had record of multiple histories of this sensor causing a CEL which were deleted (by previous owner/tech).

I reinstalled the battery and the car started up fine, I let it run a few minutes and shut it off.
Several hours later it would not start and the message "Reduced engine performance" was visible on the gauge cluster, followed by "low battery mode".
VidaDice indicated a throttle body error. ECM-P211800 throttle actuator control motor current range/performance.

Is there a simple throttle body adaption process necessary when reinstalling a battery?
I'm familiar with VW where the key needs to be in accessory mode for 30-45 seconds while the TB adapts. It is an audible high pitch whine followed by a click when complete.

Would these issues arise due to the high pressure valve cap not being present? ( the part is back ordered for several days so I'm troubleshooting in the meantime).
This part (I only need the black plastic end): https://www.volvopartswebstore.com/products/Volvo/2008/XC70/Valve/1123648/30750960.html

I charged the battery overnight and the car will start now with a very rough idle.
I'm not 100% certain if the battery is compromised somehow. Before I put my charger on it, the battery was reading 9v through VidaDice which makes no sense to me. All I did was take it out and put on my work bench for a night.

Also: on the ground wire for the battery there is a smaller wire with a yellow end. I don't recall if this was attached to anything before removal and I can't find anything it should connect to. Possibly just a ground option for aftermarket applications??

Any help would be appreciated, Thanks guys.
 

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I had the same message and same reduced engine performance problem. Mine was actually related to a throttle wiring issue. I don't remember the exact code I had though. I had these codes:
- P012023 Throttle/Pedal Position Sensor A Circuit. General Signal Failures. Signal stuck low
- P012038 Throttle/Pedal Position Sensor A Circuit. FM (Frequency Modulated) / PWM (Pulse Width Modulated) Failures. Signal

I presumed I needed a new throttle pedal without digging further and found that actually didn't fix the problem.

The problem was actually in a PWM signal wire between the throttle pedal assembly and the engine computer. I ended up running a bodge wire from the pedal assembly to a connector in the engine bay (just under the pass side headlight actually) and it's been working great since then. A bodge wire is not a great choice but it's getting the job done. The PWM signal wire that broke/shorted/whatever is VERY tiny and thin.

I don't know if this helps you or not.

The way I tackled it was to get the wiring diagrams out and figure out what all the wires on the pedal assembly were for. (there's only like 5 I think). One was a common ground I think, another power, and 2 were for the CAN connection, and 1 for the PWM to the engine computer. The PWM one sounded like it was my problem based on the codes. Then I used a multimeter to test the 'other end' of that wire at the connector under the headlight I mentioned earlier, which again I found using the wiring diagrams. I ran a temp bodge wire to test that it worked and then ran something a bit more permanent.
 

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Discussion Starter · #3 ·
Thanks for the reply jadnhm and definitely helpful as something to look into.
However, I'm thinking this issue must be related to the High pressure valve on the fuel rail. I'm just guessing here but it makes sense that it is related to the throttle body and the pressure valve cap is currently not installed correctly due to the plastic torx bit end being broken. Either that or perhaps I have a bad (NEW) fuel pressure sensor? Those are the only culprits related to the fuel system that I touched.

The current status of the car is this:
Battery charges up to 12v. I put the key in accessory mode thinking perhaps the Throttle body would need an adaption after battery hookup ( just a guess ), The car started and ran at perfect idle for 2-3 mins. Then I shut it off.
20-30 mins later, I restart the car and it immediately throws a CEL, has bad idle, "Reduced engine performance" Code, followed by "Low battery mode".

VidaDice is not showing a code for the fuel pressure sensor now.
 

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Hi Joel,
I started having exactly same issue on my 2008 v70. Replacd throttle pedal but couple of months after the issue came back.
I see that your message from about a year ago - can you confirm that it was the wiring that actually fixed the problem? Also, where could I find the wiring diagram?
Thanks so much! (I'm also sending you a PM on the same subject, not sure how notification work on here?)
Dima
 

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fixing the pedal wiring DID clear this issue up for me. I think there were 5 wires on the pedal Power +, Power -, CAN bus +, CAN bus -, and the signal wire to the ECU.

The signal wire to the ECU was TINY and was broken /somewhere/ between the pedal and the harness connector in the engine bay underneath the passenger side headlight (accessed from below).

This is all the wiring you should need I think (scrounged up from my records)
https://drive.google.com/file/d/119odVdtA-0S3dF-Xeum64ylnr7MIjR4N/view?usp=sharing
 
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