psyc0de

I recently solved my P1875 code after almost a year of it intermittently appearing. Just as I was about to drop several thousand $ on replacing the sensor, I did some problem solving and worked out a solution.

The code started appearing about 2 weeks after I installed a new head unit and small subwoofer (150w.) Symptoms were as follows:
- P1875 code thrown
- No noticeable effect on SST most of the time
- Occasional clutch disengagement as the code was thrown
- Code repeated anywhere from 3 times a day to once a month

My first instinct was electrical problems, since I just installed the sub and head unit. The head unit connected to OBDII and I read online that the SST was very sensitive to the CAN bus having electical faults. Because it was intermittent, I assumed there was a loose wire or connection that was shorting.

I ripped out my head unit and checked all of my wiring. I also checked all the wiring to the sub, which was all fine. I put everything back together and didn't get a code for another month.

After a month I started to get the codes again more frequently. About once a week or so I would notice the code being thrown with no effect still. I pulled the head unit again but everything looked fine.

I started ignoring the code at this point because I didn't want to go and search for some difficult to find electrical fault when the code could just be cleared with no problems. The code would have periods of coming and going still, but it was still infrequent enough for me not to care.

About 4 months ago I experienced a clutch disengagement with the code. That scared me, and I started to question my diagnosis of a ground fault. I noticed the transmission behaving badly on some days. I couldn't quite put my finger on the bad behavior but it just didn't feel snappy. I did a bunch more reading and saw that the torque damper sensor dies in the SST and it required a rebuild to fix.

Slowly accepting my fate of a transmission rebuild, I reached out to some local shops as well as Kozmic and SSP about my problem. Everyone said I would need to replace the sensor. Kozmic was particularly helpful in explaining what the code meant and how it affected the SST. One thing stood out to me in that conversation though; Eric said that usually you would get more problems related to reported engine speed.

As I prepared to lift out the transmission and send it to Kozmic. I couldn't shake what Eric had said. I also heard a story at a local shop where an SST tech replaced the sensor and the code still didn't go away. The more I thought about it, the more I thought my original diagnosis fit the description and it was too much of a coincidence that my stereo was installed around the same time.

Going back to my original diagnosis, I decided to pull the entire stereo wiring and redo it all to try eliminate the phantom electrical fault. No luck. I did a bunch more reading online about the code and similar codes that have no noticeable effect. The common theme I read was how sensitive the CAN bus can be.

I decided to think outside the box a bit and read up about how the sensor works. It's a hall effect sensor that works off of 7V. 7V is about half of what the battery provides, which is probably done with a /2 voltage divider and then a voltage regulator somewhere in the TCU. I looked at my idle voltage and it was at 14.1V. That's a little on the low side, and I was expecting to see a bit higher than that. Things started to make sense. Talking to a fellow electrical friend, and we thought that the stereo was drooping the voltage enough that the 7V sensor couldn't get the voltage it needed.

With a theory in place, I wondered why the voltage would drop in the first place. My friend thought it was the cheap under seat sub, which probably has little to no power smoothing and a cheap amplifier. Sure enough I realized that every time this is happening I've had music on, and probably turned up (e.g. on the highway.) I decided to test my theory by completely disconnecting the subwoofer and the 4ch amp to see if that would fix the problem. 2 weeks later with no stereo, and I hadn't had any codes. I now know that it can't be the head unit wiring.

After 2 weeks I connected the 4ch amp which is a high quality amp that was installed way after my problems started. 2 weeks later, still no codes. It was then most likely the sub. I looked at replacement subs but there's not much in the way of under seat subs, and really the stock power system should be able to handle a 150W sub. I looked at getting a cap but I read that really the battery needs to be able to handle it first.

I ordered an Optima Yellow Top and installed it to find that my idle voltage is now 14.5. I plugged the sub back in, and it's now been 2 months since I've had any codes. The transmission shifts better and doesn't have 'off' days like it used to. It's always behaving the same now.

$170 battery vs. several thousand for a rebuild and labor

I'm not completely sure if my 7V theory is correct, but it's my best guess and solved the problem!

Devgamer

This sounds exactly with my experience, i'll try disconnecting the amp and see if that improves things for me as well.

Veronica

iTrader: (2)

Seems plausible.


Reading halfway through I was 'guessing' an EMF issue (hall effect sensors are sensitive to this), but yes, I think you found it!


Now, I have a pretty powerful amp set up and no codes... [shrug]

Stevenmcgarry84

Devgamer - did you solve your issue? I have the same issue and currently trying to solve it

Bairdy

Hi,
Just joined the forum to benefit from the advice and experience of the collective! I have been having a similar problem to this and have spent much time and money trying to find the source of the problem. In a nutshell:

Car was in at Autotorque (Aylesbury, UK) for replacement shocks all round at the beginning of August. It also had a full service whilst there, including changing all fluids. After a week or so of driving the P1875 code was shown.

P1875 code is now thrown seemingly at any time; It has come on at idle; when driving at low revs; at high revs; when changing gear; when in gear; after just a few minutes of driving; after 30mins + of driving; etc..
I have replaced the torque damper sensor and clutch packs and this has made no difference. I suspect an electrical problem rather than a mechanical problem.

I read this thread with interest, and although I have not added anything electrical to the vehicle, it seems quite possible that there is a sudden drop of voltage or something similar that is triggering the fault.

I think I will try a new battery, although the battery seems fine (12V when engine off, 14v+ when engine on) there is some variation when the engine is running, occasionally dropping to 13.9V.

Jack at Autotorque suggests that the fault may be further down the electrical line (i.e. the mechatronic unit) but this will be expensive. Any ideas gratefully received.

Veronica

iTrader: (2)

A new battery may fix your issue. The old battery can develop higher or lower internal resistance with the ECU compensating for via alternator output. This might fluctuate the sensor voltage enough to take it out of range.


Check the ground cables bat to body and engine to body. Add another ground wire from engine to battery "just to be sure." see if that makes a difference before going further...

Bairdy

Thanks Veronica - I think this will be on my list of things to try next. I am taking it to the stealership tomorrow to see what they say. You never know, they might know how to fix it....?

Bairdy

Well, the stealership had no clue. Computer says there is a problem with the gearbox. Manual recommends 'buy a new gearbox'. Helpful.
Interestingly, the problem has definitely got worse. This suggests that it is not just a dodgy electrical connection, but something that is either wearing or moving slightly more out of place. The battery and ground connections are actually sound, as is the CAN bus circuit.
I will try swapping out the mechatronics unit. This seems like the next logical step. I'll post again when I have some more news.

Xoan

Hi, I have an Outlander Automatic Gearbox 2010.

After externally charging the battery and then changing it. I got the following message: transmission service required. P1875.
I have changed mechatronic unit and the error message is still showing up. I see some people talks about the "torque damper sensor", linked to the SST. I would like to know what is the SST and where is the "torque damper sensor" located ?
Thanks a lot for your help.

4G63_EVO

iTrader: (4)

Good job posting your findings, this is great info for someone else who might have a similar problem