Help with Service Engine Soon light!!
 

I have a 2001 GMC Sierra 2500 8.1 with allison transmission at about 120k. Truck has been flawless with me. It's not my daily driver just my tow vehicle. Today when I went to turn it on the Service Engine Soon light turned on. I went to the auto parts store and they hooked up their scanner to it and came back with code numbers P0847 and P0700 which both I believe have to do with the Transmission Control Module. I notice there was water dripping out of the end of the catalyc converter, didn't know if it was possibly related? When I drove the truck to the auto parts store it ran great as always. No gear shift issues or anything like that. Can someone who is more familier on this shed some light on how to go about fixing this issue? Thanks

[QUOTE=272bajadriver;3822602]I have a 2001 GMC Sierra 2500 8.1 with allison transmission at about 120k. Truck has been flawless with me. It's not my daily driver just my tow vehicle. Today when I went to turn it on the Service Engine Soon light turned on. I went to the auto parts store and they hooked up their scanner to it and came back with code numbers P0847 and P0700 which both I believe have to do with the Transmission Control Module. I notice there was water dripping out of the end of the catalyc converter, didn't know if it was possibly related? When I drove the truck to the auto parts store it ran great as always. No gear shift issues or anything like that. Can someone who is more familier on this shed some light on how to go about fixing this issue? Thanks
*


6.6 GMC 2500 code P0847
P0847 code Transmission Fluid Pressure Sensor/Switch "B" Circuit Low.

The pressure switch is the "Tin" looking part that is attached to the valvebody. Not expensive, and you don't have to remove the valve body.

Rick

The P0700 code sets when there are other transmission related codes present

Start with the p0847 fix ( above ) then clear codes and see if returns...

Rick

[QUOTE=Rwbrew3;3822605]I see you have on there 6.6 GMC I have the 8.1L 496 is the code still the same?

Sorry about that, no, not the same.. You may want to call the dealer and see about reprogramming the transmission control module ( tcm ) with the new service calibration, and have your PCM reflashed, I believe this is in there bulletin as a Fix for this problem, may even be covered, I'll try and find info and post for you .

Rick

your slipping from 4th to fifth gear and you may not have a fifth gear with the po 700 now..you usually have to clear the code,,this may have set if you have a tuner in the vehicle and or if you were towing with out using the tow haul mode..basicly the trans is slipping in higher gears..if your governor pressure is sticking or the valve is leaking then it could be the problem..like mentioned try changing it,its the biggest solenoid in the valve body..change your filter also,,try to reuse your gasket or like i would do get a new one from the dealer for 40 bucks,,they are reusable..
if problem is still their then get ahold of Arcticfriends he ie a trans guru..

Document ID# 880188
2002 Chevrolet Chevy K Silverado - 4WD

http://service.gm.com/engif/000/999/999/999999995.gif Subject:Harsh or Delayed 2-1 Downshift, Neutral Feel at a Stop, Shift Busyness, DTCs P0708, P0847, P0872, P0875, P1711, P1713 (Reprogram TCM) #02-07-30-020 - (04/22/2002)


Models:2001-02 Chevrolet and GMC C/K 2500/3500 (3/4 and 1 Ton) Series Pickup Models (Silverado and Sierra)
with Allison® Series 1000 Automatic Transmission (RPO M74)



<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=880188&pubid=271#ss1-880188">Condition

Some customers may comment on a harsh or delayed 2-1 downshift, a neutral feel at a stop or shift busyness (excessive shifting). Upon investigation, the technician may also find one or more of the following DTCs set:
• P0708
• P0847
• P0872
• P0875
• P1711
• P1713
<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=880188&pubid=271#ss2-880188">Correction

Reprogram the Transmission Control Module (TCM) with the new service calibrations which were available from Techline starting March 24, 2002 on the TIS2000 version 3.5 or later. These calibrations are electronic calibrations and are NOT available from GMSPO.
These new calibrations will address the following conditions:
2001
2002
Delayed 2-1 downshift at a stop
2-1 downshift quality concerns
Flare & bump on low speed coast-down and throttle reapply
Cold shift quality concerns
2-1 closed throttle neutral feel
*Shift busyness
Harsh 2-1 downshift
DTC P0708, P0847, P0872, P0875, P1711, P1713
Shift busyness
2-1 closed throttle neutral feel

*Important: 2002 Vehicles with 8.1L Engine --
If the concern is shift busyness, the PCM must also be reflashed to gain maximum benefit from the new TCM service calibration. This calibration was available from Techline starting March 10, 2002 on the TIS2000 version 3.0 or later. If the concern is not shift busyness, this step is not required.


This additional step is not required on vehicles with a 6.6L diesel engine (RPO LB7) or 2001 vehicles with an 8.1L engine (RPO L18).


<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=880188&pubid=271#ss3-880188">Warranty Information

For vehicles repaired under warranty, use:
Labor Operation
Description
Labor Time
K5364
Module, Transmission Control - Reprogram
0.4 hr
J6355
Powertrain Controller -- Reprogram
0.4 hr


GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.
http://service.gm.com/engif/000/999/999/999999994.gif WE SUPPORT VOLUNTARY TECHNICIAN CERTIFICATION

© Copyright General Motors Corporation. All Rights Reserved.
Does this help????

Found that info on line, good luck..

Rick

Forgot to mention the sierra 2500 hd is completely stock. I never use the tow/haul mode do you guys?

fixx
 

thats why its their,,makes a firm shift..

fixx
 

its a 01 and should have the 4l80E trans ....

Yes, always !!

Rick

Yes 4L80E, Good catch, I pulled that info off there internet page.... Guess that won't do him any good!

Sorry for the un usefull information, you had the same code as are work truck, that fixed are truck but not the same transmissions.


Rick

fixx
 

i believe 03 was the first year for the allison/8.1 combo..

BTW heres the funny part tho,,the allison shared a GM valve body tho so that may be the reason why the code are the same..

I have a 2001 3500 with the 8.1/Allison.

I will look up his codes on my Alldata.

If indeed it has a 4l80E I would first unplug trans connecter , check for corrosion, grease it with dielectric grease then replug it in and clear code. If this did not help I would then check for a TCM reflash at the dealer for affected veh vin and see what comes up, if you end up dropping the pan I would check to see if any of the pressure manifold bolts are loose, I have seen them loose before, IF you did find them loose I would drop the pressure manifold and see if the o-ring's that seal each individual switch appear to be hard or flattened too much. I also see alot of 4l80e vbodys with afl valve wear and boost valve bore wear in the pump which will screw with pressures to trans. If it is indeed a Allison I don't have much I can tell you as we rarely ever see them or troubleshoot them, Smitty

You should use the tow/haul if you are towing heavy loads. It is kind of like having a built in tuner for towing. The computer has a different program setting for stronger shifts on the trans, different shift curves to maximize torgue needed for the pull and other parameters that you will benefit from.

If you don't use the tow/haul button the PCM will figure it out as you go and adapt but it can allow some soft shifts and clutch pack slippage that will accelerate wear in the long haul.

[QUOTE=mrfixxall;3822637]i believe 03 was the first year for the allison/8.1 combo..

BTW heres the funny part tho,,the allison shared a GM valve body tho so that may be the reason why the code are the Same


Yep, that would makes sense, another good catch !!!!

Rick

OP stated it's an Allison, I was under the impression the 8.1 always came with the Allison in the trucks regardless of year, and the 4L85e in the Avalanche/ Suburban only? I know 03 had the Allison with 8.1 in the trucks.

On another note, Yes on Tow/ Haul as needed, more engine braking and way better shifting with a load, holds gears longer, and downshifts more aggressively.

They put the allison transmission in 01 with the 8.1L. Mine definitely has it and it's an 01.

According to Alldata for 2001 8.1/Allison code P0700 is a transmission MIL light request and P0847 is pressure switch manifold shift valve D problem.

Brian41 I really appreciate the help. Seems like the P0700 will just come on everytime any other code comes up. Today I'll try and find a valve d manifold pressure switch, change it and I'm sure that will cure it. Just wondering what is alldata? is that for any vehicle?

You are correct about the 700 code, it is just sent to turn on the light letting you know there is a trans code.

Alldata is a automotive information program on DVD we used when we still work on cars, I kept it because I still own cars.

Your welcome Brian

PM me your VIN number and I will check for programming updates that you may need.

Will do, I'll get the VIN tomorrow as it's the soonest I can.

I had a 2001 2500HD with an 8.1 and Allison 5speed.

I had the the same light come on once and the tranny was acting wierd. Delayed going into gear, reved then kicked hard into gear, would not switch gears, etc. Turned the truck off and trans was back to normal, but the service engine soon light was on. It ended up being the Nuetral Safety/Back up switch module. My dealer said that it was a common part to fail.

My neutral safety switch went bad also but all it affected was the cruise control.

if you have a remote start and if the wire for the trans pcm was not connected it will throw a trans code...

replace the neutral safety switch that mounts on the outside of the trans on the shift shaft,,,the original is black and the new updated one is grey and you should be all set...Iam a Trans guy at a Gm chevy shop and thats about the only thing that fails on that trans..

true,,when you remote start the truck the ecm gets 12v but NOT the shift solenoids..
the trans shift solenoids gets 12v from the ignition switch so depending on how the aftermarket remote is wired you could see stored codes when you scan data..
electric codes like po758..po756

I drove it to the auto parts store the day it threw the code and it drove fine. The store was only like 2 miles away but the truck drove fine without any hard shifting or anything.

How is the neutral switch replaced? Where exactly is it located and where does it go?

How do I test it? It was throwing code P0847 and P0700. P0847 is related to the shift valve d solenoid. I was just going to replace that solenoid, since you work on these transmissions is that what the problem is?

From what I've seen, those Allisons are like black magic, not many who really know the deal other than Diesel Tuners, GM/ Allison really locked them down, you may need to take it to a reputable dealer or GM diesel specialist, but, behind the 8.1, should be minimal issues, it takes a lot of torque to damage them but the electronics can drive you crazy at times, find a diesel/ allison specialist and have them take a look if you don't have a good dealer near you... Sorry i'm not more help, haven't owned one myself... Yet...

fixx
 

That trans is not 100 % allison,,it uses's a gm valve body with gm shift solenoids and all the sensors.

I had the dealer fix mine. Actually they replaced it twice. I had the truck in for an oil change and they replaced it at 31k because they noticed the insulation on the wires was coming off. Then at 37k(1k out of warranty), the trans started acting goofy. They ended up replacing it again as a defective part. Never had a problem after that with another 100k on the truck. Its an electronic module that is mounted on the exterior of the trans.

The park/neutral switch is mounted on the drivers side of the trans. The new updated switch comes with a heat shield to protect it from the exhaust. The old switches would melt the resin inside and seep through to the wire pigtail and glue them together often causing the plug and harness end to be replaced together. The dealer sells a replacement pigtail but they do not give it away, its more than the switch if I remember correctly. By the way this was the only issue I have ever had with my 8.1/allison.

The switch is known to be a problem but before replacing anything verify what your problem is before replacing anything as it may have nothing to do with your current code.

Well guys just wanted to give everyone an update, I went to go to the auto part store to buy the neutral safety switch the other day but when I started it up the check engine light was not on anymore. Drove it around, towed the boat and the check engine light never turned back on. Wierd but I'm not complainaing, no more check engine light so that's good.

Boatnt, brian41 and everyone else, I wanted to thank you guys for helping me and guiding me in the right direction. You guys rock!!!