Good day all. I'm a 36 year old web and graphic designer that spends hours online shopping, learning on YouTube and I must have read a million blogs by now. I consider myself tech and mech extra-savvy, BUT, this happens to be my first blog entry - sad I know! And for those of you irritated with this personal intro: take a hike, this is monumental for me.
Back to Volvo: hard shift/flare up and down on most volvos are caused by Elec issues and not mech issues I.e. software specifically designed to change the way your Volvo shifts at different temps/pressures. If your trans oil is very hot and gears go nuts - this has nothing to do with the physical I.e mechanical properties or damage. Its not dirty oil, faulty solenoids, etc. Why then does a software update or clean oil or an additional oil radiator or a magnatech filter or better engine cooling or more aircon gas etc etc solve or help the issue: cause they all ( except software update) contribute to a lower oil temp which stops the gearbox control unit changing the software to a new formula that some Volvo geek thought would be better a a warmer temp - FAIL! Hot or cold gearbox pressure not too important. Volvo software update only changes the original dumb coding a LITTLE bit therefore issues tend to resurface.
Solutions:
New tranny: RRRRR (I'm south African, replace with dollar sign or appropriate currency symbol)
Tranny rebuild: RRRR
Add radiator: RRR
New trans fluid: RR
Magnetic filter: RR
New software: RR
Etc. etc.

My solution: c ....thats right cents
Whether you have a transmission fluid temperature sensor that is housed internally (as with my v70 xc 2001) or if it is seated on gearbox this solution helps. Trick your control unit into thinking the temperature is remaining low but still climbing. Do not simply cut the wires to the sensor as this will cause issues with continuity and the control unit does need info, rather leave the sensor in the gearbox and cut its wires, splicing in a new sensor that can be housed externally in a cooler part of the engine bay that will increase in temp as car warms up, but will remain below threshold for software change ( usually 60 degrees celcius but can be more), so pick a place that will reach max 50 degrees. The temp must increase because the ecu will link it to increase in coolant temp. I initially just added a resistor, which worked for a while, but eventually kicked out code p0711 and p1618 which basically meant my car thought it was smarter than me.
You might find a cheap second hand sensor, just make sure the high and low temp range resistances are similar.

Please note all vehicles have different thermistors.

Let me know

 

Hi,
I know your post was a few years ago but I have a 2001 XC70 that is throwing the p0711/p1618 codes currently. I noticed it began shifting hard from 1st to 2nd around the same time these codes showed up (yesterday). It has been extremely hot (over 100° F) for the last few days, so I am wondering if that is affecting the temp of the transmission fluid (and everything else under the hood).
Anyway, my question is this: how detrimental is it to my car if I am unable to perform the correction you describe immediately and I continue driving (for a few days)? And does the splicing of the new sensor bypass the original? Forgive my ignorance..is this something I can do without anyone helping me? Not a car girl per SE, but I did change out a faulty ignition coil after correctly diagnosing it, and my car is not chugging anymore!
Please advise, thanks!

 

I just made another thread and this is basically what I said, mine shifts fine with the AC running, but let it sit idling with no AC or even drive with no AC the shifting changes in a negative way. Oil temp seems to be the only related thing. I would go with an external cooler rather than trick the TCM into thinking its cooler than it really is, you need that sensor giving correct info.