P0842 fault code

[Oppie]

Predictably, the morning that we were supposed to leave on vacation, the Vue
started shifting very roughly. I had filled the tank the night before so
suspected bad fuel. Put in a can of drygas and hit the highway. About 10
miles into the 200 mile trip, the MIL light came on. Pulled over and started
pulling fuses (the lw300 ECU could be reset by pulling the controls B+
fuse). No dice, couldn't find a fuse that would turn off the light. Drove
all the way with the transmission slamming from gear to gear. It was like
the torque converter stayed locked up. Interesting that the shifter normally
defaults to 3rd gear when you shift to manual and you can shift up or down
from there. Now the manual defaults to 4th gear and the up/down buttons are
not functional.

Finally made it to destination (enduring wife's diatribes that we bought a
POS) and after unloading the car, fished out my AutoTap tool and laptop.
Showed P0842 "transmission fluid pressure sensor "A" circuit Low." I haven't
been able to make sense of this yet. Did a reset of the fault codes and car
is driving fine now. Drove it for about 50 miles today and light has not
come back on. It likely will so looking for possible causes.

2009 Vue XE with 2.4L EcoTec and 4T45 base model transmission

[SMS]

Either the sensor is flaky or pressure switch manifold is flaky.

If you have an Android phone or tablet you should buy Torque Pro from
the Play store and buy a Bluetooth ELM327 module for the OBDII socket;
for less than $20, you'll always have an OBDII scan tool with you.

<https://play.google.com/store/apps/details?id=org.prowl.torque&hl=en>
<http://dx.com/s/142679>

Unfortunately, due to Apple not supporting the proper Bluetooth
protocol, there's no equivalent app for iOS.

[Oppie]

"SMS" <scharf...@geemail.com> wrote in message
news:52178092$0$52779$742e...@news.sonic.net...

I have the XP laptop we travel with and always have the Autotap reader in
the car. Bummer that iOS doesn't support the proper Bluetooth protocol since
I have an iPod Touch. There are lots of hits though if one googles for
"bluetoogh obdii" which would work with the laptop too.
Been looking for options to update from Autotap since B&B Electronics,
owner of Autotap, discontinued sales and support. It works well and can give
me live data for the engine parameters only but will show fault codes for
the entire system.

Going back to the original thread, no further hiccups since I reset the code
last Wednesday. When we get home from vacation, I'll check in with dealer.
I'll check the wiring for harness flex/abrasions and connectors for
oxidation first.

The service manual I had bought in PDF form turned out to be severely
lacking and did not have any of the fault code troubleshooting data. Only
spent $15 on it and have an agreement with the seller to upgrade to the full
set of GM DVD ROMs for a small additional payment.

[SMS]

On 8/24/2013 8:06 AM, Oppie wrote:

> I have the XP laptop we travel with and always have the Autotap reader
> in the car. Bummer that iOS doesn't support the proper Bluetooth
> protocol since I have an iPod Touch. There are lots of hits though if
> one googles for "bluetoogh obdii" which would work with the laptop too.

There's some Wi-Fi OBDII dongles that work with iOS but the apps for
OBDII for iOS aren't nearly as good at Torque Pro, plus they are much
more expensive. It's almost worth buying an el-cheapo Android phone from
Virgin Mobile and not activating it.

[Oppie]

Looks like the pressure switch has three signals, A, B and C. High = battery
voltage and low = 0 Volts. For all normal conditions, the A line is always
high. Any open circuit either due to a bad sensor (inside transmission),
broken or intermittent connection (including oxidized contacts on
connectors) would give this code.