2003 GMC Sierra Tranny Issue

I have a 2003 GMC Sierra with a 4.3L V6, automatic transmission, and 2WD. It has ~107K miles on it currently.

I have travelled alot recently and has sat for 2 weeks out of the last 6 months and been driven sparingly in the 2 weeks I'm home. When I start it up I find that the fan and RPMs on the engine are typically high for the first 15-20 minutes and the tranny shifts at higher RPMs than normal but then returns to normal.

Yesterday however I found that I it is having those same symptoms and it has very little power and acceleration until I get over 20 MPH. I drove it for a while last night and today and it is still exhibiting the same issue. I have been home and driving it alot for the last 2 weeks as well and it has behaved normal duing that period.

I have recently tuned the truck up, put a new air cleaner, and PCV valve. I also ran some injector cleaner through the tank on a 250 mile drive, the day before the symptoms began.

There is no grinding or non-normal noises and the truck has the normal power/acceleration/torque in reverse and past 20MPH. The truck appears to just be shifting late in 1st gear and having little to no acceleration/torque until 20MPH.

I suspect it's a vacuum hose (some to the canister on the drivers side of the engine compartment) or mass airflow sensor, any other thoughts on potential causes? If you think it's any of the above, can you please indicate where in the engine compartment or chassis the component is located.

Thanks.

John

John D 28 said:

I have a 2003 GMC Sierra with a 4.3L V6, automatic transmission, and 2WD. It has ~107K miles on it currently.

I have travelled alot recently and has sat for 2 weeks out of the last 6 months and been driven sparingly in the 2 weeks I'm home. When I start it up I find that the fan and RPMs on the engine are typically high for the first 15-20 minutes and the tranny shifts at higher RPMs than normal but then returns to normal.

Yesterday however I found that I it is having those same symptoms and it has very little power and acceleration until I get over 20 MPH. I drove it for a while last night and today and it is still exhibiting the same issue. I have been home and driving it alot for the last 2 weeks as well and it has behaved normal duing that period.

I have recently tuned the truck up, put a new air cleaner, and PCV valve. I also ran some injector cleaner through the tank on a 250 mile drive, the day before the symptoms began.

There is no grinding or non-normal noises and the truck has the normal power/acceleration/torque in reverse and past 20MPH. The truck appears to just be shifting late in 1st gear and having little to no acceleration/torque until 20MPH.

I suspect it's a vacuum hose (some to the canister on the drivers side of the engine compartment) or mass airflow sensor, any other thoughts on potential causes? If you think it's any of the above, can you please indicate where in the engine compartment or chassis the component is located.

Thanks.

John

Click to expand...

Start with the simple and clean your throttle body with throttle body cleaner and replace your TPS (Throttle Position Sensor) and your thermostat. The PCM takes readings from your TPS and engine temperature, if the readings are not correct. The PCM may still have it on a open loop to try and get the engine to it's normal operation temperature and a faulty TPS will also cause delays in the shifting of the transmission and other transmission issues.

Good luck and keep us posted. Check TPS for smooth and linear electrical response over the entire range of motion. If not, then replace before you buy a new one or do the Salvage Yard for $15.00.

In calling the parts store, they seemed to think it's more likely it would be related to the Catalytic converter but maybe the throttle body items.

I don't agree with this as it proforms as normal in reverse and at higher speeds. In addition, the transition has been quick and had no previous symptoms before this latest bit.

I just wanted to have a better feeling from someone with more experience than me before I go and get a line...

Any chance it's related to the cat?

Thanks.

John

John D 28 said:

In calling the parts store, they seemed to think it's more likely it would be related to the Catalytic converter but maybe the throttle body items.

I don't agree with this as it proforms as normal in reverse and at higher speeds. In addition, the transition has been quick and had no previous symptoms before this latest bit.

I just wanted to have a better feeling from someone with more experience than me before I go and get a line...

Any chance it's related to the cat?

Thanks.

John

Click to expand...

You would get a service engine light come on if you have a Catalytic Converter issue. You can get under the Sierra and bang on the Catalytic and see if there is rattling. Common for the inside of the Catalytic to break apart and cause restriction, but that is most likely throughout your whole engine RPM range.

If you think it could be your Catalytic converter, take it to a Muffler shop and most of them will inspect free of charge. Being a 03, your Catalytic converter could have fallen apart and will need to be replaced.

Keep us posted and good luck.

So...interesting and cheap resolution to this one.

I went out to my truck and the check engine light was now on. I went to my local Advance Auto where they allowed me to use their scanner for free and got the following codes:

P0740 - Torque Converter Clutch Circuit Malfunction

P0785 - Shift/Timing Solenoid Malfunction

P1860 - TCC PWM Solenoid Circuit Electrical


So in speaking with the clerk and talking through the suggestions, we both thought the error codes pointed else where. He had seen this same exact issue before with another GMC (Jimmy with the 4.3). He had taken the code reader and deleted the codes out of the vehicle memory and then drove it and the issue has never come back on that other vehicle (several months ago).

I did the same procedure on my vehicle and it is now back to shifting normal and having the correct power/acceleration.

The catalyst for this appears to be water. The GMC jimmy had been through a large mud puddle apparently and that's when it's issue started. My truck was through a very large rain storm that fogged up the windows of my truck like I've never seen before on any vehicle.

So far so good, and it cost nothing at all.

Thanks for the support!

So last night it began having the check engine light. I went down to the local parts store and used their scanner and got the following codes:

P0740 - Torque Converter Clutch Circuit Malfunction

P0785 - Shift/Timing Solenoid Malfunction

P1860 - TCC PWM Solenoid Circuit Electrical


http://www.obd-codes.com/trouble_codes/gm/
http://www.freeautomechanic.com/diagnostictroublecodes6.html
(where I got the description of the codes)

The person at the counter had seen 2 of the 3 codes prior on an GMC jimmy with the 4.3 after it had gone through a major mud puddle. He had simply deleted the codes out of the vehicle's memory and that truck went back to running normal (has been running for several months now with no issue).

We had a major rain out here the day that the issue began. The rain was to the point that when I got out of work the inside of my truck was fogged up for about 25 minutes.

I took his suggestion and cleared the codes from my GMC Sierra's memory and found that it didn't quite work right the first time. However running the truck for a bit and restarting it a few times after that seemed to clear it.

Either way, it's running like normal now and cost $0 to fix.

Thanks for the support Molson!

John

So it turns out later that day I had a check engine light come on and had a couple of codes. P0785, P0740, and P1860 you can find all of these using google.

Turns out that the major rain we had the day that the issue had started caused the issue. The person at the local hardware store had seen these codes on a GMC jimmy after the driver went through a major puddle. In both instances, simply using programmer to delete the codes out of the vehicle error log memory cleared the issues.

John D 28 said:

So it turns out later that day I had a check engine light come on and had a couple of codes. P0785, P0740, and P1860 you can find all of these using google.

Turns out that the major rain we had the day that the issue had started caused the issue. The person at the local hardware store had seen these codes on a GMC jimmy after the driver went through a major puddle. In both instances, simply using programmer to delete the codes out of the vehicle error log memory cleared the issues.

Click to expand...

Clearing the codes will not fix the issues. The codes you have given are related to the Torque Converter, With all of those transmission symptoms and codes. This may indicate a failure in the harness that the transmission communicates through. Might have it checked to make sure it is connected well.

Second thought is that the transmission has a bunch of miles and could be close to the end of its life. If poor shifting and performance is occurring you may be in for a decent repair. All those solenoids are replaceable and can be purchased for around $20.00 each, but no guarantee that this will completely fix the problems.

If your lucky, it's just going to be a bad harness connection. The connection is located on the passenger side by the Catalytic converter, make sure the connections are damage free and good.

Visit a local trans shop and have them do a line pressure test on the pressure test port and go for a drive to verify proper line pressure. Base pressure at idle in P,N,OD should be around 70psi and around 140psi in R. Max line pressure should be at least 190psi at WOT in 1st or 2nd, 225psi is optimum. If base pressure is low, trans or pump is worn out. If max pressure is low, check EPC solenoid. If reverse is slow to engage, and line pressure does not come up to at least 130psi in reverse, replace the boost valve with a Transgo 0.094" or 0.500" boost valve (easy fix in pan) and swap out your servo with Corvette servo's on the side of the transmission.

This will bring back life to your transmission and buy some more miles and time without replacing the transmission if all the internal seals are good and clutches. http://www.sonnax.com/instructions/HP-4L60E-01-IN.pdf